Microglial activation and brain injury after intracerebral hemorrhage

Hypothermia and temperature modulation for intracerebral hemorrhage (ICH): pathophysiology and translational applications

Background

Intracerebral hemorrhage (ICH) still poses a substantial challenge in clinical medicine because of the high morbidity and mortality rate that characterizes it. This review article expands into the complex pathophysiological processes underlying primary and secondary neuronal death following ICH. It explores the potential of therapeutic hypothermia as an intervention to mitigate these devastating effects.

Methods

A comprehensive literature review to gather relevant studies published between 2000 and 2023.

Discussion

Primary brain injury results from mechanical damage caused by the hematoma, leading to increased intracranial pressure and subsequent structural disruption. Secondary brain injury encompasses a cascade of events, including inflammation, oxidative stress, blood-brain barrier breakdown, cytotoxicity, and neuronal death. Initial surgical trials failed to demonstrate significant benefits, prompting a shift toward molecular mechanisms driving secondary brain injury as potential therapeutic targets. With promising preclinical outcomes, hypothermia has garnered attention, but clinical trials have yet to establish its definitive effectiveness. Localized hypothermia strategies are gaining interest due to their potential to minimize systemic complications and improve outcomes. Ongoing and forthcoming clinical trials seek to clarify the role of hypothermia in ICH management.

Conclusion

Therapeutic hypothermia offers a potential avenue for intervention by targeting the secondary injury mechanisms. The ongoing pursuit of optimized cooling protocols, localized cooling strategies, and rigorous clinical trials is crucial to unlocking the potential of hypothermia as a therapeutic tool for managing ICH and improving patient outcomes.

Potential therapeutic effects of Nrf2 activators on intracranial hemorrhage

Intracranial hemorrhage (ICH) is a devastating disease which induces high mortality and poor outcomes including severe neurological dysfunctions. ICH pathology is divided into two types: primary brain injury (PBI) and secondary brain injury (SBI). Although there are numerous preclinical studies documenting neuroprotective agents in experimental ICH models, no effective drugs have been developed for clinical use due to complicated ICH pathology. Oxidative and inflammatory stresses play central roles in the onset and progression of brain injury after ICH, especially SBI. Nrf2 is a crucial transcription factor in the anti-oxidative stress defense system. Under normal conditions, Nrf2 is tightly regulated by the Keap1. Under ICH pathological conditions, such as overproduction of reactive oxygen species (ROS), Nrf2 is translocated into the nucleus where it up-regulates the expression of several anti-oxidative phase II enzymes such as heme oxygenase-1 (HO-1). Recently, many reports have suggested the therapeutic potential of Nrf2 activators (including natural or synthesized compounds) for treating neurodegenerative diseases. Moreover, several Nrf2 activators attenuate ischemic stroke-induced brain injury in several animal models. This review summarizes the efficacy of several Nrf2 activators in ICH animal models. In the future, Nrf2 activators might be approved for the treatment of ICH patients.

Mitochondrial Uncouplers Confer Protection by Activating AMP-Activated Protein Kinase to Inhibit Neuroinflammation Following Intracerebral Hemorrhage

Intracerebral hemorrhage (ICH) is a disease with high disability and mortality rates. Currently, the efficacy of therapies available for ICH is limited. Microglia-mediated neuroinflammation substantially exacerbates brain damage following ICH. Here, we investigated whether mitochondrial uncouplers conferred protection by suppressing neuroinflammation following ICH. To mimic ICH-induced neuroinflammation in vitro, we treated microglia with red blood cell (RBC) lysate. RBC lysate enhanced the expression of pro-inflammatory cytokines in microglia. A clinically used uncoupler, niclosamide (Nic), reduced the RBC lysate-induced expression of pro-inflammatory cytokines in microglia. Moreover, Nic ameliorated brain edema, decreased neuroinflammation, and improved neurological deficits in a well-established mouse model of ICH. Like niclosamide, the structurally unrelated uncoupler carbonyl cyanide p-triflouromethoxyphenylhydrazone (FCCP) reduced brain edema, decreased neuroinflammation, and improved neurological deficits following ICH. It has been reported that mitochondrial uncouplers activate AMP-activated protein kinase (AMPK). Mechanistically, Nic enhanced AMPK activation following ICH, and AMPK knockdown abolished the beneficial effects of Nic following ICH. In conclusion, mitochondrial uncouplers conferred protection by activating AMPK to inhibit microglial neuroinflammation following ICH.

A pro-inflammatory mediator USP11 enhances the stability of p53 and inhibits KLF2 in intracerebral hemorrhage

Microglial cell activation and neuroinflammation after intracerebral hemorrhage (ICH) lead to secondary brain damage. Ubiquitin-specific protease 11 (USP11) has been correlated with ICH-induced neuron apoptosis. This study aims to explore the molecular mechanism of USP11 regulating neuroinflammation in ICH. First, an ICH rat model was developed by intracranial administration of collagenase. Silencing USP11 was found to alleviate nerve injury in rats with ICH-like symptoms. Then, through loss- and gain-of-function assays, USP11 knockdown was revealed to alleviate ICH-induced symptoms, corresponding to reduced modified neurological severity scores (mNSS) value, brain water content, blood-brain barrier permeability, neuron apoptosis, microglial cell activation, neutrophil infiltration, and inflammatory factor secretion. It was subsequently shown in microglial cells that USP11 stabilized p53 by deubiquitination and p53 targeted the Kruppel-like factor 2 (KLF2) promoter to repress KLF2 transcription, thereby activating the nuclear factor κB (NF-κB) pathway. Further, rescue experiments were conducted in vivo to validate the function of the USP11/p53/KLF2/NF-κB axis in ICH-induced inflammation, which confirmed that USP11 silencing blocked the release of pro-inflammatory cytokines following ICH by downregulating p53, thus protecting against neurological impairment. Hence silencing USP11 may be a novel anti-inflammatory method for ICH treatment.

Brain injury and repair after intracerebral hemorrhage: The role of microglia and brain-infiltrating macrophages

Intracerebral hemorrhage (ICH) is a major public health problem characterized by cerebral bleeding. Despite recent advances in preclinical studies, there is no effective treatment for ICH making it the deadliest subtype of stroke. The lack of effective treatment options partly attributes to the complexity as well as poorly defined pathophysiology of ICH. The emerging evidence indicates the potential of targeting secondary brain damage and hematoma resolution for improving neurological outcomes after ICH. Herein, we provide an overview of our understanding of the functional roles of activated microglia and brain-infiltrating monocyte-derived macrophages in brain injury and repair after ICH. The clinical and preclinical aspects that we discuss in this manuscript are related to ICH that occurs in adults, but not in infants. Also, we attempt to identify the knowledge gap in the field for future functional studies given the potential of targeting microglia and brain-infiltrating macrophages for therapeutic intervention after ICH.

The Role of Thrombin in Brain Injury After Hemorrhagic and Ischemic Stroke

Thrombin is increased in the brain after hemorrhagic and ischemic stroke primarily due to the prothrombin entry from blood either with a hemorrhage or following blood-brain barrier disruption. Increasing evidence indicates that thrombin and its receptors (protease-activated receptors (PARs)) play a major role in brain pathology following ischemic and hemorrhagic stroke (including intracerebral, intraventricular, and subarachnoid hemorrhage). Thrombin and PARs affect brain injury via multiple mechanisms that can be detrimental or protective. The cleavage of prothrombin into thrombin is the key step of hemostasis and thrombosis which takes place in every stroke and subsequent brain injury. The extravascular effects and direct cellular interactions of thrombin are mediated by PARs (PAR-1, PAR-3, and PAR-4) and their downstream signaling in multiple brain cell types. Such effects include inducing blood-brain-barrier disruption, brain edema, neuroinflammation, and neuronal death, although low thrombin concentrations can promote cell survival. Also, thrombin directly links the coagulation system to the immune system by activating interleukin-1α. Such effects of thrombin can result in both short-term brain injury and long-term functional deficits, making extravascular thrombin an understudied therapeutic target for stroke. This review examines the role of thrombin and PARs in brain injury following hemorrhagic and ischemic stroke and the potential treatment strategies which are complicated by their role in both hemostasis and brain.

miR-146a alleviates the apoptosis of hippocampal neurons induced by microglia activation via targeting TRAF6

OBJECTIVE

To identify the role of miR-146a and tumor necrosis factor receptor-associated factor 6 (TRAF6) for improving the apoptosis of hippocampal neurons induced by microglia activation.

METHODS

Mouse microglial cell line (BV2 cell) was employed and treated with lipopolysaccharide. Mouse hippocampal nerve cell line (HT22 cell) was then grown in BV2 conditioned medium, and miR-146a overexpression and silencing cell lines were constructed. CCK8 and clone formation test were utilized to evaluate the proliferation ability of the transfected cells, and the level of inflammatory factors was measured by ELISA. Apoptosis was determined extensively by flow cytometry. The apoptosis-related protein and TRAF6 protein expressions were verified by Western blot. TRAF6 was identified to be the target gene of miR-146a based on double Luciferase Report. Finally, both TRAF6 and miR-146a were used to treat HT22 cells and the above indexes were detected repeatedly.

RESULTS

Interleukin (IL)-1β, tumor necrosis factor-α, and IL-6 expressions in BV2 cells increased significantly. miR-146a overexpression distinctly increased the cell proliferation ability and B-cell lymphoma-2 expression ((Bcl-2, p < 0.05); meanwhile, the apoptosis rate of cells, apoptosis-related proteins (Bcl-2 associated X and cleaved caspase-3), and TRAF6 gene and protein expressions were significantly decreased (p < 0.05). However, these above results were reversed for miR-146a silence. There is a targeting relationship between miR-146a and TRAF6. Silencing TRAF6 gene can promote HT22 cells' proliferation and inhibit apoptosis. The effect of miR-146a on HT22 cells was reversed by adding TRAF6 mimics to miR-146a overexpression cells.

CONCLUSION

miR-146a can inhibit the apoptosis of hippocampal neurons caused by microglia activation via targeting TRAF6 and down-regulating its expression.

Loss of mural cell-derived laminin aggravates hemorrhagic brain injury

Background

Mural cells synthesize and deposit laminin to the basement membrane. To investigate the function of mural cell-derived laminin, we generated a mutant mouse line lacking mural cell-derived laminin (termed PKO). In a previous study, we showed that the PKO mice were grossly normal under homeostatic condition, but developed blood-brain barrier (BBB) breakdown with advanced age (> 8 months), suggesting that these mutants are intrinsically weak. Based on these findings, we hypothesized that PKO mice have exacerbated injuries in pathological conditions.

Methods

Using collagenase-induced intracerebral hemorrhage (ICH) as an injury model, we examined various stroke outcomes, including hematoma volume, neurological function, neuronal death, BBB integrity, paracellular/transcellular transport, inflammatory cell infiltration, and brain water content, in PKO mice and their wildtype littermates at young age (6–8 weeks). In addition, transmission electron microscopy (TEM) analysis and an in vitro ICH model were used to investigate the underlying molecular mechanisms.

Results

Compared to age-matched wildtype littermates, PKO mice display aggravated stroke outcomes, including larger hematoma size, worse neurological function, increased neuronal cell death, enhanced BBB permeability, increased transcytosis, and elevated inflammatory cell infiltration. These mutants also exhibit high baseline brain water content independent of aquaporin-4 (AQP4). In addition, mural cell-derived laminin significantly reduced caveolin-1 without affecting tight junction proteins in the in vitro ICH model.

Conclusions

These results suggest that mural cell-derived laminin attenuates BBB damage in ICH via decreasing caveolin-1 and thus transcytosis, regulates brain water homeostasis, and plays a beneficial role in ICH.

Neuroinflammation after Intracerebral Hemorrhage and Potential Therapeutic Targets

Spontaneous intracerebral hemorrhage (ICH) is a catastrophic illness causing significant morbidity and mortality. Despite advances in surgical technique addressing primary brain injury caused by ICH, little progress has been made treating the subsequent inflammatory cascade. Pre-clinical studies have made advancements identifying components of neuroinflammation, including microglia, astrocytes, and T lymphocytes. After cerebral insult, inflammation is initially driven by the M1 microglia, secreting cytokines (e.g., interleukin-1β [IL-1β] and tumor necrosis factor-α) that are involved in the breakdown of the extracellular matrix, cellular integrity, and the blood brain barrier. Additionally, inflammatory factors recruit and induce differentiation of A1 reactive astrocytes and T helper 1 (Th1) cells, which contribute to the secretion of inflammatory cytokines, augmenting M1 polarization and potentiating inflammation. Within 7 days of ICH ictus, the M1 phenotype coverts to a M2 phenotype, key for hematoma removal, tissue healing, and overall resolution of inflammation. The secretion of anti-inflammatory cytokines (e.g., IL-4, IL-10) can drive Th2 cell differentiation. M2 polarization is maintained by the secretion of additional anti-inflammatory cytokines by the Th2 cells, suppressing M1 and Th1 phenotypes. Elucidating the timing and trigger of the anti-inflammatory phenotype may be integral in improving clinical outcomes. A challenge in current translational research is the absence of an equivalent disease animal model mirroring the patient population and comorbid pathophysiologic state. We review existing data and describe potential therapeutic targets around which we are creating a bench to bedside translational research model that better reflects the pathophysiology of ICH patients.

Pathophysiological Mechanisms and Potential Therapeutic Targets in Intracerebral Hemorrhage

Intracerebral hemorrhage (ICH) is a subtype of hemorrhagic stroke with high mortality and morbidity. The resulting hematoma within brain parenchyma induces a series of adverse events causing primary and secondary brain injury. The mechanism of injury after ICH is very complicated and has not yet been illuminated. This review discusses some key pathophysiology mechanisms in ICH such as oxidative stress (OS), inflammation, iron toxicity, and thrombin formation. The corresponding therapeutic targets and therapeutic strategies are also reviewed.

AAV/BBB-Mediated Gene Transfer of CHIP Attenuates Brain Injury Following Experimental Intracerebral Hemorrhage

Cell death is a hallmark of secondary brain injury following intracerebral hemorrhage (ICH). The E3 ligase CHIP has been reported to play a key role in mediating necroptosis-an important mechanism of cell death after ICH. However, there is currently no evidence supporting a function of CHIP in ICH. In the present study, we aimed to determine whether CHIP plays an essential role in brain injury after ICH. Our findings indicated that CHIP expression was increased in the peri-hematomal area in rat models of ICH. The AAV/BBB viral platform enables non-invasive, widespread, and long-lasting global neural expression of target genes. Treatment with AAV/BBB-CHIP ameliorated brain injury and inhibited neuronal necroptosis and inflammation in wild type (WT) rats following ICH. Furthermore, rats with CHIP deficiency experienced severe brain injury and increased levels of neuronal necroptosis and inflammation relative to their WT counterparts. However, treatment with AAV/BBB-CHIP attenuated the effects of CHIP deficiency after ICH. Collectively, our results demonstrate that CHIP inhibits necroptosis and pathological inflammation following ICH, and that overexpression of CHIP may represent a therapeutic intervention for ICH. Moreover, the AAV/BBB viral platform may provide a novel avenue for the treatment of brain injury.

Role and mechanisms of cytokines in the secondary brain injury after intracerebral hemorrhage

Intracerebral hemorrhage (ICH) is a common and severe cerebrovascular disease that has high mortality. Few survivors achieve self-care. Currently, patients receive only symptomatic treatment for ICH and benefit poorly from this regimen. Inflammatory cytokines are important participants in secondary injury after ICH. Increases in proinflammatory cytokines may aggravate the tissue injury, whereas increases in anti-inflammatory cytokines might be protective in the ICH brain. Inflammatory cytokines have been studied as therapeutic targets in a variety of acute and chronic brain diseases; however, studies on ICH are limited. This review summarizes the roles and functions of various pro- and anti-inflammatory cytokines in secondary brain injury after ICH and discusses pathogenic mechanisms and emerging therapeutic strategies and directions for treatment of ICH.

Cab45s inhibits neuronal apoptosis following intracerebral hemorrhage in adult rats

Recent studies have shown that Cab45s, belonging to the CREC family, can fight against apoptosis in the cancer cell lines. Here, we report that Cab45s may involve in neuronal apoptosis at the early stage of intracerebral hemorrhage (ICH) in pathophysiology. We found that expression of Cab45s was enhanced in areas contiguous to hematoma following ICH in adult rats, and that so were the expressions of Glucose-regulated protein 78 (GRP78), pro-apoptotic Bcl-2-associated X protein (Bax) and active caspase-3. In vitro, coimmunoprecipitation analysis indicated the interaction between Cab45s and GRP78. Depletion of Cab45s attenuated the expression of GRP78, but increased the expressions of Bax and caspase-3 in PC12 cells treated with hemin, which finally promoted apoptosis. Together, these results reveal that Cab45s might exert its anti-apoptotic function against neuronal apoptosis. Thus, the study may provide evidences for regulating Cab45s as a potentially reliable treatment for the secondary damage following ICH.

Colony stimulating factor 1 receptor inhibition eliminates microglia and attenuates brain injury after intracerebral hemorrhage

Microglia are the first responders to intracerebral hemorrhage, but their precise role in intracerebral hemorrhage remains to be defined. Microglia are the only type of brain cells expressing the colony-stimulating factor 1 receptor, a key regulator for myeloid lineage cells. Here, we determined the effects of a colony-stimulating factor 1 receptor inhibitor (PLX3397) on microglia and the outcome in the context of experimental mouse intracerebral hemorrhage. We show that PLX3397 effectively depleted microglia, and the depletion of microglia was sustained after intracerebral hemorrhage. Importantly, colony-stimulating factor 1 receptor inhibition attenuated neurodeficits and brain edema in two experimental models of intracerebral hemorrhage induced by injection of collagenase or autologous blood. The benefit of colony-stimulating factor 1 receptor inhibition was associated with reduced leukocyte infiltration in the brain and improved blood-brain barrier integrity after intracerebral hemorrhage, and each observation was independent of lesion size or hematoma volume. These results demonstrate that suppression of colony-stimulating factor 1 receptor signaling ablates microglia and confers protection after intracerebral hemorrhage.

Depletion of microglia exacerbates postischemic inflammation and brain injury

Brain ischemia elicits microglial activation and microglia survival depend on signaling through colony-stimulating factor 1 receptor (CSF1R). Although depletion of microglia has been linked to worse stroke outcomes, it remains unclear to what extent and by what mechanisms activated microglia influence ischemia-induced inflammation and injury in the brain. Using a mouse model of transient focal cerebral ischemia and reperfusion, we demonstrated that depletion of microglia via administration of the dual CSF1R/c-Kit inhibitor PLX3397 exacerbates neurodeficits and brain infarction. Depletion of microglia augmented the production of inflammatory mediators, leukocyte infiltration, and cell death during brain ischemia. Of note, microglial depletion-induced exacerbation of stroke severity did not solely depend on lymphocytes and monocytes. Importantly, depletion of microglia dramatically augmented the production of inflammatory mediators by astrocytes after brain ischemia . In vitro studies reveal that microglia restricted ischemia-induced astrocyte response and provided neuroprotective effects. Our findings suggest that neuroprotective effects of microglia may result, in part, from its inhibitory action on astrocyte response after ischemia.

Overexpression of GRP75 inhibits inflammation in a rat model of intracerebral hemorrhage

Glucose‑regulated protein 75 (GRP75) is a member of the heat shock protein 70 family and previous studies have demonstrated that GRP75 is involved in diseases of the central nervous system. However, the biological function of GRP75 in intracerebral hemorrhage (ICH) remains to be clarified. Thus, the aim of the present study was to evaluate the effects of GRP75 in a rat model of ICH. Western blotting was used to detect the protein expression of GRP75, active caspase‑3, Bax, Bcl‑2, p‑Akt and Akt in brain tissues following ICH. The levels of tumor necrosis factor‑α (TNF‑α) and interleukin (IL)‑1β were evaluated using ELISA assay. Expression of GRP75 mRNA and protein was demonstrated to be reduced in the brain tissues of rats with ICH compared with sham‑operated rats. In addition, overexpression of GRP75 in brain tissues with ICH significantly inhibited the production of the inflammatory cytokines TNF‑α and IL-1β and increased Bcl‑2/decreased Bax levels compared with ICH alone. Furthermore, overexpression of GRP75 in brain tissues with ICH resulted in significantly increased phosphorylation of Akt compared with ICH alone. Therefore, the present study demonstrated, for the first time to the best of our knowledge, significantly reduced GRP75 expression in brain tissues following ICH, and that overexpression of GRP75 inhibits inflammation and potentially inhibits neuronal apoptosis in a rat model of ICH. GRP75 may, therefore, represent a promising target in the treatment of ICH.

Activation of peroxisome proliferator-activated receptor-γ by a 12/15-lipoxygenase product of arachidonic acid: a possible neuroprotective effect in the brain after experimental intracerebral hemorrhage

OBJECTIVE In this study, the authors investigated the involvement of 15( S)-hydroxyeicosatetraenoic acid (15(S)-HETE) in the regulation of peroxisome proliferator-activated receptor-γ (PPARγ) after intracerebral hemorrhage (ICH) and its effects on hemorrhage-induced inflammatory response and oxidative stress in an experimental rodent model. METHODS To simulate ICH in a rat model, the authors injected autologous whole blood into the right striatum of male Sprague-Dawley rats. The distribution and expression of 12/15-lipoxygenase (12/15-LOX) were determined by immunohistochemistry and Western blot analysis, respectively. Immunofluorescent double labeling was used to study the cellular localization of 12/15-LOX, and 15(S)-HETE was measured with a 15(S)-HETE enzyme immunoassay kit. Neurological deficits in the animals were assessed through behavioral testing, and apoptotic cell death was determined with terminal deoxynucleotidyl transferase-mediated biotinylated dUTP nick-end labeling. RESULTS Rats with ICH had increased expression of 12/15-LOX predominantly in neurons and also in oligodendrocytes, astrocytes, and microglia. Moreover, ICH elevated production of 15(S)-HETE in the brain area ipsilateral to the blood injection. The PPARγ agonist, exogenous 15(S)-HETE, significantly increased PPARγ protein levels and increased PPARγ-regulated gene (i.e., catalase) expression in the ICH rats. Reduced expression of the gene for the proinflammatory protein nuclear factor κB coincided with decreased neuron damage and improved functional recovery from ICH. A PPARγ antagonist, GW9662, reversed the effects of exogenous 15(S)-HETE on the PPARγ-regulated genes. CONCLUSIONS The induction of 15(S)-HETE during simulated ICH suggests generation of endogenous signals of neuroprotection. The effects of exogenous 15(S)-HETE on brain hemorrhage-induced inflammatory responses and oxidative stress might be mediated via PPARγ.

IDH1 Associated with Neuronal Apoptosis in Adult Rats Brain Following Intracerebral Hemorrhage

Isocitrate dehydrogenase 1 (IDH1), one member of the IDH family can convert isocitrate to α-ketoglutarate (α-KG) via oxidative decarboxylation. IDH1 and IDH2 mutations have been identified in multiple tumor types and the mutations confer neomorphic activity in the mutant protein, resulting in the conversion of α-KG to the oncometabolite, D-2-hydroxyglutarate (2-HG). The subsequent accumulation of 2-HG results in epigenetic dysregulation via inhibition of α-KG-dependent histone and DNA demethylase. And the glutamate levels are reduced in IDH mutant cells compared to wild-type. We have known that diffuse gliomas contain a high frequency of mutations in the IDH1 gene. However, the expression of IDH1 and its roles in Intracranial hemorrhage (ICH) remain largely unknown. We observed increased expression of IDH1 in neurons after intracerebral hemorrhage. Up-regulation of IDH1 was found to be accompanied by the increased expression of active caspase-3 and pro-apoptotic Bcl-2-associated X protein and decreased expression of anti-apoptotic protein B cell lymphoma-2 in vivo and vitro studies. So we hypothesized that IDH1 was involved in the regulation of neuronal apoptosis. The present research for the first time detected the expression and variation of IDH1 surrounding the hematoma, and all data proved the involvement of IDH1 in neuronal apoptosis following ICH.

Elevated serum IL-11, TNF α, and VEGF expressions contribute to the pathophysiology of hypertensive intracerebral hemorrhage (HICH)

To study the changes in serum interleukin-11 (IL-11), tumor necrosis factor-α (TNF-α) and vascular endothelial growth factor (VEGF) expressions following hypertensive intracerebral hemorrhage (HICH), and explore their associations with disease severity and prognosis. Serum IL-11, TNF-α, and VEGF levels after 1, 3, 7, and 14 days after HICH were assayed using enzyme-linked immunosorbent assay (ELISA), and neurological deficit score (NDS) were recorded at admission and discharge for 99 HICH cases. Then 45 healthy controls were included and assayed for serum IL-11, TNF-α, and VEGF levels. Serum IL-11, TNF-α, and VEGF levels were higher in HICH patients than healthy controls (all P < 0.05). TNF-α was higher at the 3rd day following disease onset than other time points (all P < 0.05), while IL-11 and VEGF peaked at the 7th day and dropped below baseline values at the 14th day (all P < 0.05). Serum IL-11 was positively correlated with TNF-α (r = 0.70, P < 0.05) and VEGF (r = 0.72, P < 0.05). Serum TNF-α was positively correlated with VEGF (r = 0.46, P < 0.05). Serum IL-11, TNF-α, and VEGF were associated with disease severity in HICH patients. Patients with more severe disease tended to have higher NDS at admission, and higher IL-11, TNF-α, and VEGF during treatment were associated with higher NDS at discharge. Serum IL-11, TNF-α, and VEGF may involve in the pathophysiology of HICH, thus IL-11, TNF-α, and VEGF may be prognostic factors for post HICH neurologic damage.

Increased Expression of Ubiquitin-Specific Protease 4 Participates in Neuronal Apoptosis After Intracerebral Hemorrhage in Adult Rats

Ubiquitinating enzymes catalyze protein ubiquitination, a reversible process countered by deubiquitinating enzyme (DUB) action. Ubiquitin-specific protease 4 (USP4) is a member of the ubiquitin-specific protease (USP) family of DUBs that has a role in spliceosome regulation. In the present study, we demonstrated that USP4 may be involved in neuronal apoptosis in the processes of intracerebral hemorrhage (ICH). We obtained a significant up-regulation of USP4 in neurons adjacent to the hematoma following ICH by the results of Western blot, immunohistochemistry, and immunofluorescence. Increasing USP4 level was found to be accompanied by the up-regulation of active caspase-3, γH2AX, Bax, and decreased expression of Bcl-2. In addition, USP4 co-localized well with γH2AX in the nucleus in the ICH model and hemin-induced apoptosis model. Moreover, in vitro study, knocking down USP4 by USP4-specific siRNA in PC12 cells reduced active caspase-3 expression. All these results above suggested that USP4 may be involved in neuronal apoptosis after ICH.

Functional outcome after intracerebral haemorrhage – a review of the potential role of antiapoptotic agents

Intracerebral haemorrhage (ICH) is the second most common form of stroke and is associated with greater mortality and morbidity compared with ischaemic stroke. The current ICH management strategies, which mainly target primary injury mechanisms, have not been shown to improve patient’s functional outcome. Consequently, multimodality treatment approaches that will focus on both primary and secondary pathophysiology have been suggested. During the last decade, a proliferation of experimental studies has demonstrated the role of apoptosis in secondary neuronal loss at the periphery of the clot after ICH. Subsequently, the value of certain antiapoptotic agents in reducing neuronal death and improving functional outcome following ICH was evaluated in animal models. Preliminary evidence from those studies strongly supports the potential role of antiapoptotic agents in reducing neuronal death and improving functional outcome after intracerebral haemorrhage. Expectedly, the ongoing and subsequent clinical trials will substantiate these findings and provide clear information on the most potent and safe antiapoptotic agents, their appropriate dosage, and temporal window of action, thereby making them suitable for the multimodality treatment approach.

Treatment with TO901317, a synthetic liver X receptor agonist, reduces brain damage and attenuates neuroinflammation in experimental intracerebral hemorrhage

Background

Intracerebral hemorrhage (ICH) induces a series of inflammatory processes that contribute to neuronal damage and neurological deterioration. Liver X receptors (LXRs) are nuclear receptors that negatively regulate transcriptional processes involved in inflammatory responses, but their role in the pathology following ICH remains unclear. The present study investigated the neuroprotective effects and anti-inflammatory actions of TO901317, a synthetic LXR agonist, in a model of collagenase-induced ICH and in microglial cultures.

Methods

Mice subjected to collagenase-induced ICH injury were injected with either TO901317 (30 mg/kg) or vehicle 10 min after ICH and subsequently daily for 2 days. Behavioral studies, histology analysis, and assessments of hematoma volumes, brain water content, and blood-brain barrier (BBB) permeability were performed. The protein expression of LXR-α, LXR-β, ATP binding cassette transporter-1 (ABCA-1), and inflammatory molecules was analyzed. The anti-inflammatory mechanism of TO901317 was investigated in cultured microglia that were stimulated with either lipopolysaccharide (LPS) or thrombin.

Results

ICH induced an increase in LXR-α protein levels in the hemorrhagic hemisphere at 6 h whereas LXR-β expression remained unaffected. Both LXR-α and LXR-β were expressed in neurons and microglia in the peri-ICH region and but rarely in astrocytes. TO901317 significantly attenuated functional deficits and brain damage up to 28 days post-ICH. TO901317 also reduced neuronal death, BBB disruption, and brain edema at day 4 post-ICH. These changes were associated with marked reductions in microglial activation, neutrophil infiltration, and expression levels of inflammatory mediators at 4 and 7 days. However, TO901317 had no effect on matrix metalloproteinase-9 activity. In BV2 microglial cultures, TO901317 attenuated LPS- and thrombin-stimulated nitric oxide production and reduced LPS-induced p38, JNK, MAPK, and nuclear factor-kappa B (NF-κB) signaling. Moreover, delaying administration of TO901317 to 3 h post-ICH reduced brain tissue damage and neuronal death.

Conclusions

Our results suggest that enhancing LXR activation may provide a potential therapy for ICH by modulating the cytotoxic functions of microglia.

Electronic supplementary material

The online version of this article (doi:10.1186/s12974-016-0524-8) contains supplementary material, which is available to authorized users.

Microglial Polarization and Inflammatory Mediators After Intracerebral Hemorrhage

Intracerebral hemorrhage (ICH) is a subtype of stroke with high mortality and morbidity. When a diseased artery within the brain bursts, expansion and absorption of the resulting hematoma trigger a series of reactions that cause primary and secondary brain injury. Microglia are extremely important for removing the hematoma and clearing debris, but they are also a source of ongoing inflammation. This article discusses the role of microglial activation/polarization and related inflammatory mediators, such as Toll-like receptor 4, matrix metalloproteinases, high-mobility group protein box-1, nuclear factor erythroid 2-related factor 2, heme oxygenase, and iron, in secondary injury after ICH and highlights the potential targets for ICH treatment.

Treadmill exercise promotes neuroprotection against cerebral ischemia-reperfusion injury via downregulation of pro-inflammatory mediators

BACKGROUND

Stroke is one of the major causes of morbidity and mortality worldwide, which is associated with serious physical deficits that affect daily living and quality of life and produces immense public health and economic burdens. Both clinical and experimental data suggest that early physical training after ischemic brain injury may reduce the extent of motor dysfunction. However, the exact mechanisms have not been fully elucidated. The aim of this study was to investigate the effects of aerobic exercise on neuroprotection and understand the underlying mechanisms.

MATERIALS AND METHODS

Middle cerebral artery occlusion (MCAO) was conducted to establish a rat model of cerebral ischemia-reperfusion injury to mimic ischemic stroke. Experimental animals were divided into the following three groups: sham (n=34), MCAO (n=39), and MCAO plus treadmill exercise (n=28). The effects of aerobic exercise intervention on ischemic brain injury were evaluated using functional scoring, histological analysis, and Bio-Plex Protein Assays.

RESULTS

Early aerobic exercise intervention was found to improve motor function, prevent death of neuronal cells, and suppress the activation of microglial cells and astrocytes. Furthermore, it was observed that aerobic exercise downregulated the expression of the cytokine interleukin-1β and the chemokine monocyte chemotactic protein-1 after transient MCAO in experimental rats.

CONCLUSION

This study demonstrates that treadmill exercise rehabilitation promotes neuroprotection against cerebral ischemia-reperfusion injury via the downregulation of proinflammatory mediators.

Effects of Aerobic Capacity on Thrombin-Induced Hydrocephalus and White Matter Injury

We have previously shown that intracerebral hemorrhage-induced brain injury is less in rats bred for high aerobic capacity (high capacity runners; HCR) compared with those bred for low aerobic capacity (low capacity runners; LCRs). Thrombin, an essential component in the coagulation cascade, is produced after cerebral hemorrhage. Intraventricular injection of thrombin causes significant hydrocephalus and white matter damage. In the present study, we examined the effect of exercise capacity on thrombin-induced hydrocephalus and white matter damage. Mid-aged (13-month-old) female LCRs (n = 13) and HCRs (n = 12) rats were used in this study. Rats received an intraventricular injection of thrombin (3 U, 50 μl). All rats underwent magnetic resonance imaging (MRI) at 24 h and were then euthanized for brain histology and Western blot. The mortalities were 20 % in LCRs and 33 % in HCRs after thrombin injection (p > 0.05). No rats died after saline injection. Intraventricular thrombin injection resulted in hydrocephalus and periventricular white matter damage as determined on MRI. In LCR rats, thrombin induced significant ventricle enlargement (23.0 ± 2.3 vs12.8 ± 1.9 mm(3) in LCR saline group; p < 0.01) and white matter lesion (9.3 ± 7.6 vs 0.6 ± 0.5 mm(3) in LCR saline group, p < 0.05). In comparison, in HCR rats thrombin induced less ventricular enlargement (17.3 ± 3.9 vs 23.0 ± 2.3 mm(3) in LCRs, p < 0.01) and smaller white matter lesions (2.6 ± 1.2 mm(3) vs 9.3 ± 7.6 mm(3) in LCRs, p < 0.05). In LCR rats, there was also upregulation of heat shock protein-32, a stress marker, and microglial activation in the periventricular white matter. These changes were significantly reduced in HCR rats. Intraventricular injection of thrombin caused more white matter damage and hydrocephalus in rats with low aerobic capacity. A differential effect of thrombin may contribute to differences in the effects of cerebral hemorrhage with aerobic capacity.

EP3, Prostaglandin E2 Receptor Subtype 3, Associated with Neuronal Apoptosis Following Intracerebral Hemorrhage

EP3 is prostaglandin E2 receptor subtype 3 and mediates the activation of several signaling pathways, changing in cAMP levels, calcium mobilization, and activation of phospholipase C. Previous studies demonstrated a direct role for EP3 in various neurodegenerative disorders, such as stroke and Alzheimer disease. However, the distribution and function of EP3 in ICH diseases remain unknown. Here, we demonstrate that EP3 may be involved in neuronal apoptosis in the processes of intracerebral hemorrhage (ICH). From the results of Western blot and immunohistochemistry, we obtained a significant up-regulation of EP3 in neurons adjacent to the hematoma following ICH. Up-regulation of EP3 was found to be accompanied by the increased expression of active caspase-3 and pro-apoptotic Bcl-2-associated X protein (Bax) and decreased expression of anti-apoptotic protein B cell lymphoma-2 (Bcl-2) in vivo and vitro studies. Furthermore, the expression of these three proteins reduced active caspase-3 and Bax expression, while increased Bcl-2 were changed after knocking down EP3 by RNA interference in PC12 cells, further confirmed that EP3 might exert its pro-apoptotic function on neuronal apoptosis. Thus, EP3 may play a role in promoting the neuronal apoptosis following ICH.

Up-Regulation of KPNB1 Involves in Neuronal Apoptosis Following Intracerebral Hemorrhage in Adult Rats

Kpnb1, also known as Importin β1, is a member of the Karyopherin protein family which plays a important role in nuclear import and export pathways. Its expression has been shown to be responsive to stress, such as heat shock, ethanol and oxidative stress. Previous studies demonstrated that Kpnb1 had anti-apoptotic in cervical cancer. These together prompted us to explore whether Kpnb1 has some association with neuron apoptosis in the pathophysiology of intracerebral hemorrhage (ICH). In our study, an ICH model was established by injecting into the right basal ganglia of adult rats with their autologous whole blood and assessed by behavioral tests. We found Kpnb1 were significantly up-regulated adjacent to the hematoma following ICH by Western blot and immunohistochemistry. Double immunofluorenscence manifested Kpnb1 was strikingly increased in neurons, not astrocytes or microglia. Furthermore, we also found that kpnb1 had co-localizations with active-caspase-3 which is a neuronal apoptosis marker suggesting its role in neuronal apoptosis. What's more, our in vitro study, using Kpnb1 RNA interference in PC12 cells, further indicated that Kpnb1 might exert its pro-apoptotic function on neuronal apoptosis. Therefore, Kpnb1 may play a role in the neuronal apoptosis following ICH.

Cannabinoid receptor 2 attenuates microglial accumulation and brain injury following germinal matrix hemorrhage via ERK dephosphorylation in vivo and in vitro

Microglia accumulation plays detrimental roles in the pathology of germinal matrix hemorrhage (GMH) in the immature preterm brain. However, the underlying mechanisms remain poorly defined. Here, we investigated the effects of a cannabinoid receptor 2 (CB2R) agonist on microglia proliferation and the possible involvement of the mitogen-activated protein kinase (MAPK) family pathway in a collagenase-induced GMH rat model and in thrombin-induced rat microglia cells. We demonstrated that activation of CB2R played a key role in attenuating brain edema, neuronal degeneration, microglial accumulation and the phosphorylated extracellular signal-regulated kinase (p-ERK) protein level 24 h following GMH. In vitro, Western blot analysis and immunostaining indicated that ERK and P38 phosphorylation levels in microglia stimulated by thrombin were decreased after JWH-133 (CB2R selective agonist) treatment in a concentration-dependent manner. Microglia proliferation (EDU + microglia) and inflammatory and oxidative stress responses were attenuated by UO126 (ERK pathway inhibitor) 24 h after thrombin stimulation, an activity that was prevented by AM630 (CB2R selective antagonist). Overall, these findings suggest that activation of the endocannabinoid system might attenuate inflammation-induced secondary brain injury after GMH in rats by reducing microglia accumulation through a mechanism involving ERK dephosphorylation. Enhancing CB2R activation is a potential treatment to slow down the course of GMH in preterm newborns.

Neuronal tumour necrosis factor-α and interleukin-1β expression in a porcine model of intracerebral haemorrhage: Modulation by U-74389G

Tumour necrosis factor α (TNF-α) and interleukin 1β (IL-1β) are important mediators of intracerebral haemorrhage (ICH) inflammatory response. Lazaroids, established antioxidants and neuroprotectants, have been studied in several brain pathologies. The present study was designed to investigate: a) TNF-α and IL-1β changes, in neurons and b) U-74389G effects, 4 and 24h after haematoma induction in a porcine model of intracerebral haemorrhage. In twenty male landrace pigs (swines) aged 135-150 days old, autologous whole blood was injected around the right basal ganglia territory; in ten of the pigs the lazaroid compound U-74389G was administered. Brain TNF-α and IL-1β immunopositive neurons were determined by immunoarray techniques at 4 and 24h timepoints. After the haematoma induction the number of TNF-α immunopositive neurons ipsilateral to the haematoma was significantly higher compared to the contralateral site at 4h (p<0.0005), while U-74389G significantly reduced the number of TNF-α immunopositive neurons, ipsilateral to the haematoma, at 4h (p=0.002); at 24h, TNF-α immunopositive neurons were found significantly lower in the control group ipsilateral to the haematoma in comparison to 4h timepoint(p<0.0005). The number of IL-1β immunopositive neurons at 4h after the hematoma induction was significantly higher ipsilateral to the haematoma site (p<0.0005). U-74389G had no statistical significant effect. TNF-α and IL-1β, increase in neurons, 4h after the haematoma induction, ipsilateral to the haematoma site. The administration of the antioxidant compound U-74389G, results in early (at 4h) decrease of TNF-α immunopositive neurons but shows no statistical significant effect to IL-1β immunopossitive neurons.

Intercellular cross-talk in intracerebral hemorrhage

Intracerebral hemorrhage (ICH) is a devastating cerebrovascular disorder with high mortality and morbidity. Currently, there are few treatment strategies for ICH-induced brain injury. A recent increase in interest in the pathophysiology of ICH has led to elucidation of the pathways underlying ICH-induced brain injury, pathways where intercellular and hematoma to cell signaling play important roles. In this review, we summarize recent advances in ICH research focusing on intercellular and hematoma:cell cross-talk related to brain injury and recovery after ICH. This article is part of a Special Issue entitled SI: Cell Interactions In Stroke.

The role of the microglia in acute CNS injury

Microglia are considered the brain's resident immune cell involved in immune defense, immunocompetence, and phagocytosis. They maintain tissue homeostasis within the brain and spinal cord under normal condition and serves as its initial host defense system. However, when the central nervous system (CNS) faces injury, microglia respond through signaling molecules expressed or released by neighboring cells. Microglial responses are dual in nature. They induce a nonspecific immune response that may exacerbate CNS injury, especially in the acute stages, but are also essential to CNS recovery and repair. The full range of microglial mechanisms have yet to be clarified, but there is accumulating knowledge about microglial activation in acute CNS injury. Microglial responses require hours to days to fully develop, and may present a therapeutic target for intervention with a much longer window of opportunity compare to other neurological treatments. The challenge will be to find ways to selectively suppress the deleterious effects of microglial activation without compromising its beneficial functions. This review aims to provide an overview of the recent progress relating on the deleterious and beneficial effect of microglia in the setting of acute CNS injury and the potential therapeutic intervention against microglial activation to CNS injury.

Protective Effect of Pyrroloquinoline Quinone (PQQ) in Rat Model of Intracerebral Hemorrhage

Pyrroloquinoline quinone (PQQ) has invoked considerable interest because of its presence in foods, antioxidant properties, cofactor of dehydrogenase, and amine oxidase. Protective roles of PQQ in central nervous system diseases, such as experimental stroke and spinal cord injury models have been emerged. However, it is unclear whether intracerebral hemorrhage (ICH), as an acute devastating disease, can also benefit from PQQ in experimental conditions. Herein, we examined the possible effect of PQQ on neuronal functions following ICH in the adult rats. The results showed that rats pretreated with PQQ at 10 mg/kg effectively improved the locomotor functions, alleviated the hematoma volumes, and reduced the expansion of brain edema after ICH. Also, pretreated rats with PQQ obviously reduced the production of reactive oxygen species after ICH, probably due to its antioxidant properties. Further, we found that, Bcl-2/Bax, the important indicator of oxidative stress insult in mitochondria after ICH, exhibited increasing ratio in PQQ-pretreated groups. Moreover, activated caspase-3, the apoptotic executor, showed coincident alleviation in PQQ groups after ICH. Collectively, we speculated that PQQ might be an effective and potential neuroprotectant in clinical therapy for ICH.

CHMP4B, ESCRT-III associating protein, associated with neuronal apoptosis following intracerebral hemorrhage

Charged multivesicular body protein (CHMP) represents a family of small helical proteins that contain an N-terminal basically charged region and a smaller C-terminal acidic region, which are highly conserved in all eukaryotes. CHMP4B, a core component of the endosomal sorting complex required for transport (ESCRT)-III, is requisite for endosomal sorting and other biological processes. Here, we demonstrate that CHMP4B may be involved in neuronal apoptosis in the processes of intracerebral hemorrhage (ICH). From the results of Western blot, immunohistochemistry and immunofluorescence, we obtained a significant up-regulation of CHMP4B in neurons adjacent to the hematoma following ICH. Increasing CHMP4B level was found to be accompanied by the up-regulation of Fas receptor (Fas), Fas ligand (FasL), active caspase-8, and active caspase-3. Besides, CHMP4B co-localized well with Fas and active caspase-3 in neurons, indicating its potential role in neuronal apoptosis. What's more, our in vitro study, using CHMP4B RNA interference in PC12 cells, further confirmed that CHMP4B might exert its pro-apoptotic function on neuronal apoptosis through extrinsic pathway. Thus, CHMP4B may play a role in promoting the brain damage following ICH.

Up-regulation of Glis2 involves in neuronal apoptosis after intracerebral hemorrhage in adult rats

The novel Krüppel-like zinc finger protein Gli-similar 2 (Glis2), one member of the transcription factors, is involved in controlling the flow of genetic information and the modulation of diverse cellular activities. Accumulating evidence has demonstrated its important roles in adult development and several diseases. However, information regarding the regulation and possible function of Glis2 in the central nervous system is still limited. In this study, we explored the roles of Glis2 during the pathophysiological process of intracerebral hemorrhage (ICH). An ICH rat model was established and assessed by behavioral tests. Expression of Glis2 was significantly up-regulated in brain areas surrounding the hematoma following ICH. Immunofluorescence showed that Glis2 was strikingly increased in neurons, but not astrocytes or microglia. Up-regulation of Glis2 was found to be accompanied by the increased expression of active caspase-3 and Bax and decreased expression of Bcl-2 in vivo and vitro studies. Moreover, knocking down Glis2 by RNA-interference in PC12 cells reduced active caspase-3 and Bax expression while increased Bcl-2. Collectively, we speculated that Glis2 might exert pro-apoptotic function in neurons following ICH.

Progress in translational research on intracerebral hemorrhage: is there an end in sight?

Intracerebral hemorrhage (ICH) is a common and often fatal stroke subtype for which specific therapies and treatments remain elusive. To address this, many recent experimental and translational studies of ICH have been conducted, and these have led to several ongoing clinical trials. This review focuses on the progress of translational studies of ICH including those of the underlying causes and natural history of ICH, animal models of the condition, and effects of ICH on the immune and cardiac systems, among others. Current and potential clinical trials also are discussed for both ICH alone and with intraventricular extension.

Human amniotic epithelial stem cells inhibit microglia activation through downregulation of tumor necrosis factor-α, interleukin-1β and matrix metalloproteinase-12 in vitro and in a rat model of intracerebral hemorrhage

BACKGROUND AIMS

The molecular mechanisms by which stem cell transplantation improves functional recovery after intracerebral hemorrhage (ICH) are not well understood. Accumulating evidence suggests that microglia cells are activated shortly after ICH and that this activation contributes to secondary ICH-induced brain injury. We studied the effect of human amniotic epithelial stem cells (HAESCs) on microglia activation.

METHODS

To study the effect of HAESCs in vitro, we used thrombin to activate the microglia cells. Twenty-four hours after thrombin treatment, the levels of tumor necrosis factor-α and interleukin-1β were measured by enzyme-linked immunosorbent assay. In vivo, the HAESCs were transplanted into the rat striatum 1 day after collagenase-induced ICH. The expression levels of matrix metalloproteinase (MMP)-12 and microglia infiltration in the peri-hematoma tissues were determined 7 days after ICH through the use of reverse transcriptase-polymerase chain reaction and immunohistochemical analysis, respectively.

RESULTS

Thrombin-activated microglia expression of tumor necrosis factor-α, interleukin-1β and MMP-12 was significantly reduced through contact-dependent and paracrine mechanisms when the HAESCs were co-cultured with microglia cells. After transplantation of HAESCs in rat brains, the expression levels of MMP-12 and microglia infiltration in the peri-hematoma tissues were significantly reduced.

CONCLUSIONS

Our observations suggest that microglia activation could be inhibited by HAESCs both in vitro and in vivo, which may be an important mechanism by which the transplantation of HAESCs reduces brain edema and ameliorates the neurologic deficits after ICH. Therefore, we hypothesize that methods for suppressing the activation of microglia and reducing the inflammatory response can be used for designing effective treatment strategies for ICH.

Correlation between serum IL-1beta levels and cerebral edema extent in a hypertensive intracerebral hemorrhage rat model

BACKGROUND

Interleukin-1beta (IL-1beta) is a pro-inflammatory cytokine that is increased following hypertensive intracerebral hemorrhage (ICH), potentially related to neural damage by cerebral edema.

OBJECTIVE

To investigate the correlation between post-ICH serum IL-1beta and cerebral edema in a hypertensive rat model.

METHODS

We used 30 successful ICH male spontaneously hypertensive rats (SHR) subjected to autologous blood infusion and displaying behavioral abnormalities (ICH group), and 30 sham-operated rats. Cerebral edema was assessed at 8, 16, 24, 48, 72, and 120 hours using dry and wet right hemisphere weighing, and serum IL-1beta levels were determined by enzyme-linked immunosorbent assay (ELISA). Nonlinear regression was performed between serum IL-1beta levels and cerebral edema extent at different time intervals after ICH.

RESULTS

No significant difference was observed in preoperative blood pressure between the two groups. In ICH rats, behavioral abnormalities were observed at all time points except at 120 hours Intracerebral hemorrhage rats exhibited significantly increased serum IL-1beta levels between 16 and 72 hours, and increased cerebral edema between 24 and 72 hours (all P < 0·05 vs sham-operated rats), but no significant differences were found in the sham-operated group. Serum IL-1beta and cerebral edema in the ICH group returned to baseline by 120 hours Serum IL-1beta levels were positively correlated with cerebral edema (r  =  0·906, P  =  0·001).

CONCLUSION

Serum IL-1beta was related to cerebral edema extent in hypertensive ICH rats, which may eventually be useful as an indicator for progression of cerebral edema after ICH, and contributing to the choice of a treatment strategy.

Increased expression of T cell immunoglobulin and mucin domain 3 aggravates brain inflammation via regulation of the function of microglia/macrophages after intracerebral hemorrhage in mice

Background

Microglia/macrophages are known to play important roles in initiating brain inflammation after spontaneous intracerebral hemorrhage (ICH). T cell immunoglobulin and mucin domain-3 (Tim-3) have been proven to play a critical part in several inflammatory diseases through regulation of both adaptive and innate immune responses. Tim-3 can be expressed by microglia/macrophages and regulates their function in the innate immune response. However, the effect of Tim-3 on inflammatory responses following ICH is unclear.

Methods

In this study, we investigated Tim-3 expression, the inflammatory cytokines tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β), and brain water content in peri-hematomal brain tissue at 12 hours and at 1, 3, 5, and 7 days post-ICH in wild type (WT) ICH and Tim-3^−/− ICH mice. The numbers of Tim-3 positive cells,astrocytes, neutrophils and microglia/macrophages were detected using immunofluorescence staining. Cytokines were measured by ELISA. Double immunoflurorescence labeling was performed to identify the cellular source of Tim-3 expression. Mouse neurological deficit scores were assessed through animal behavior.

Results

Expression of Tim-3 increased early in mouse peri-hematomal brain tissue after autologous blood injection, peaked at day 1, and was positively correlated with the concentrations of TNF-α, IL-1β, and brain water content. Tim-3 was predominantly expressed in microglia/macrophages. Compared with WT mice, Tim-3^−/− mice had reduced ICH-induced brain inflammation with decreased TNF-α and IL-1β, cerebral edema and neurological deficit scores. Moreover, Tim-/- inhibited activation of microglia/macrophages. The number of activated microglia/macrophages in Tim-3^−/− ICH mice was much lower than that in WT ICH mice.

Conclusions

Our findings demonstrate that Tim-3 plays an important role in brain inflammation after ICH, and may be a potential treatment target.

Inflammation in intracerebral hemorrhage: from mechanisms to clinical translation

Intracerebral hemorrhage (ICH) accounts for 10-15% of all strokes and is associated with high mortality and morbidity. Currently, no effective medical treatment is available to improve functional outcomes in patients with ICH. Potential therapies targeting secondary brain injury are arousing a great deal of interest in translational studies. Increasing evidence has shown that inflammation is the key contributor of ICH-induced secondary brain injury. Inflammation progresses in response to various stimuli produced after ICH. Hematoma components initiate inflammatory signaling via activation of microglia, subsequently releasing proinflammatory cytokines and chemokines to attract peripheral inflammatory infiltration. Hemoglobin (Hb), heme, and iron released after red blood cell lysis aggravate ICH-induced inflammatory injury. Danger associated molecular patterns such as high mobility group box 1 protein, released from damaged or dead cells, trigger inflammation in the late stage of ICH. Preclinical studies have identified inflammatory signaling pathways that are involved in microglial activation, leukocyte infiltration, toll-like receptor (TLR) activation, and danger associated molecular pattern regulation in ICH. Recent advances in understanding the pathogenesis of ICH-induced inflammatory injury have facilitated the identification of several novel therapeutic targets for the treatment of ICH. This review summarizes recent progress concerning the mechanisms underlying ICH-induced inflammation. We focus on the inflammatory signaling pathways involved in microglial activation and TLR signaling, and explore potential therapeutic interventions by targeting the removal of hematoma components and inhibition of TLR signaling.

Microglial responses after ischemic stroke and intracerebral hemorrhage

Stroke is a leading cause of death worldwide. Ischemic stroke is caused by blockage of blood vessels in the brain leading to tissue death, while intracerebral hemorrhage (ICH) occurs when a blood vessel ruptures, exposing the brain to blood components. Both are associated with glial toxicity and neuroinflammation. Microglia, as the resident immune cells of the central nervous system (CNS), continually sample the environment for signs of injury and infection. Under homeostatic conditions, they have a ramified morphology and phagocytose debris. After stroke, microglia become activated, obtain an amoeboid morphology, and release inflammatory cytokines (the M1 phenotype). However, microglia can also be alternatively activated, performing crucial roles in limiting inflammation and phagocytosing tissue debris (the M2 phenotype). In rodent models, microglial activation occurs very early after stroke and ICH; however, their specific roles in injury and repair remain unclear. This review summarizes the literature on microglial responses after ischemic stroke and ICH, highlighting the mediators of microglial activation and potential therapeutic targets for each condition.

Tumor necrosis factor α antagonism improves neurological recovery in murine intracerebral hemorrhage

Background

Intracerebral hemorrhage (ICH) is a devastating stroke subtype characterized by a prominent neuroinflammatory response. Antagonism of pro-inflammatory cytokines by specific antibodies represents a compelling therapeutic strategy to improve neurological outcome in patients after ICH. To test this hypothesis, the tumor necrosis factor alpha (TNF-α) antibody CNTO5048 was administered to mice after ICH induction, and histological and functional endpoints were assessed.

Methods

Using 10 to 12-week-old C57BL/6J male mice, ICH was induced by collagenase injection into the left basal ganglia. Brain TNF-α concentration, microglia activation/macrophage recruitment, hematoma volume, cerebral edema, and rotorod latency were assessed in mice treated with the TNF-α antibody, CNTO5048, or vehicle.

Results

After ICH induction, mice treated with CNTO5048 demonstrated reduction in microglial activation/macrophage recruitment compared to vehicle-treated animals, as assessed by unbiased stereology (P = 0.049). This reduction in F4/80-positive cells was associated with a reduction in cleaved caspase-3 (P = 0.046) and cerebral edema (P = 0.026) despite similar hematoma volumes, when compared to mice treated with vehicle control. Treatment with CNTO5048 after ICH induction was associated with a reduction in functional deficit when compared to mice treated with vehicle control, as assessed by rotorod latencies (P = 0.024).

Conclusions

Post-injury treatment with the TNF-α antibody CNTO5048 results in less neuroinflammation and improved functional outcomes in a murine model of ICH.