Evidence of CCR2-independent transmigration of Ly6C hi monocytes into the brain after permanent cerebral ischemia in mice

Ccr2 Gene Ablation Does Not Influence Seizure Susceptibility, Tissue Damage, or Cellular Inflammation after Murine Pediatric Traumatic Brain Injury

Pediatric traumatic brain injury (TBI) is a major public health issue, and a risk factor for the development of post-traumatic epilepsy that may profoundly impact the quality of life for survivors. As the majority of neurotrauma research is focused on injury to the adult brain, our understanding of the developing brain's response to TBI remains incomplete. Neuroinflammation is an influential pathophysiological mechanism in TBI, and is thought to increase neuronal hyperexcitability, rendering the brain more susceptible to the onset of seizures and/or epileptogenesis. We here hypothesized that peripheral blood-derived macrophages, recruited into the injured brain via C-C motif ligand 2 (CCL2) chemokine/C-C chemokine receptor type 2 (CCR2) signaling, contributes to neuroinflammation and thus seizure susceptibility after experimental pediatric TBI. Using Ccr2 gene-deficient mice in the controlled cortical impact (CCI) model of TBI, in 3-week-old male mice we found that TBI led to an increase in susceptibility to pentylenetetrazol (PTZ)-evoked seizures, associated with considerable cortical tissue loss, a robust cellular neuroinflammatory response, and oxidative stress. Intriguingly, although Ccr2-deficiency increased CCL2 levels in serum, it did not exacerbate seizure susceptibility or the neuroinflammatory cellular response after pediatric TBI. Similarly, acute post-injury treatment with a CCR2 antagonist did not influence seizure susceptibility or the extent of tissue damage in wild-type (WT) mice. Together, our findings suggest that CCR2 is not a crucial driver of epileptogenesis or neuroinflammation after TBI in the developing brain. We propose that age may be an important factor differentiating our findings from previous studies in which targeting CCL2/CCR2 has been reported to be anti-inflammatory, neuroprotective or anti-seizure.

The Role of CCL2/CCR2 Axis in Cerebral Ischemia-Reperfusion Injury and Treatment: From Animal Experiments to Clinical Trials

C-C motif chemokine ligand 2 (CCL2) is a member of the monocyte chemokine protein family, which binds to its receptor CCR2 to induce monocyte infiltration and mediate inflammation. The CCL2/CCR2 signaling pathway participates in the transduction of neuroinflammatory information between all types of cells in the central nervous system. Animal studies and clinical trials have shown that CCL2/CCR2 mediate the pathological process of ischemic stroke, and a higher CCL2 level in serum is associated with a higher risk of any form of stroke. In the acute phase of cerebral ischemia-reperfusion, the expression of CCL2/CCR2 is increased in the ischemic penumbra, which promotes neuroinflammation and enhances brain injury. In the later phase, it participates in the migration of neuroblasts to the ischemic area and promotes the recovery of neurological function. CCL2/CCR2 gene knockout or activity inhibition can reduce the nerve inflammation and brain injury induced by cerebral ischemia-reperfusion, suggesting that the development of drugs regulating the activity of the CCL2/CCR2 signaling pathway could be used to prevent and treat the cell injury in the acute phase and promote the recovery of neurological function in the chronic phase in ischemic stroke patients.

Bim Deletion Reduces Functional Deficits Following Ischemic Stroke in Association with Modulation of Apoptosis and Inflammation

Cellular apoptosis is a key pathological mechanism contributing to neuronal death following ischemic stroke. The pro-apoptotic Bcl-2 family protein, Bim, is an important regulator of apoptosis. In this study we investigated the effect of Bim expression on post-stroke functional outcomes, brain injury and inflammatory mechanisms. Wild type (WT) and Bim-deficient mice underwent 1-h middle cerebral artery occlusion (MCAO) followed by 23 h of reperfusion. At 24-h post-stroke, we assessed functional deficit, infarct volume, immune cell death, as well as the number of infiltrating immune cells in the brain and circulating immune cells. Bim deficiency did not affect infarct volume (P > 0.05), but resulted in less motor impairment (~ threefold greater latency to fall in hanging grip strength test, P < 0.05) and a lower median clinical score than WT mice (P < 0.05). Additionally following MCAO, Bim-deficient mice exhibited fewer myeloid cells (particularly neutrophils) in the ischemic brain hemisphere and less apoptosis of CD3⁺ T cells in the spleen and thymus compared with WT (all P < 0.05). After MCAO, Bim-deficient mice also tended to have more M2-polarised macrophages in the brain than WT mice. In sham-operated mice, we found that Bim deficiency resulted in greater numbers of circulating total CD45⁺ leukocytes, Ly6C^lo+ monocytes and CD3⁺ T cells, although MCAO did not affect the number of circulating cells at 24 h in either genotype. Our findings suggest that Bim deficiency modulates post-stroke outcomes, including reductions in motor impairment, brain inflammation and systemic post-stroke leukocyte apoptosis. Bim could therefore serve as a potential therapeutic target for stroke.

Large-Scale Multivariate Analysis to Interrogate an Animal Model of Stroke: Novel Insights Into Poststroke Pathology

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Downregulation of miR-23b by transcription factor c-Myc alleviates ischemic brain injury by upregulating Nrf2

Ischemic brain injury (IBI) is a common acute cerebral vessel disease that occurs secondary to blockage in arteries, mainly characterized by insufficient blood supply to the brain. The transcription factor c-Myc in IBI continues to be implicated in numerous studies. This study was conducted with emphasis placed on the underlying mechanism of c-Myc in IBI. Clinical samples were collected from IBI patients. Middle cerebral artery occlusion (MCAO) was induced in mice by inserting a suture from the external carotid artery to the anterior cerebral artery through the internal carotid artery to mechanically block the blood supply at the origin of the middle cerebral artery, and cortical neurons from mice were exposed to oxygen glucose deprivation (OGD) conditions for IBI model in vitro construction. RT-qPCR was performed to determine microRNA-23b (miR-23b) expression. TUNEL staining and Western blot analysis was conducted to detect apoptosis. The regulatory relationship was analyzed by dual-luciferase reporter gene assay. After loss- and gain-of-function assays, triphenyltetrazolium chloride staining was carried out to detect the area of cerebral infarction, after which the spatial memory in mice was evaluated with Morris water maze test. As per our findings, miR-23b was upregulated in the serum of IBI patients and OGD-treated murine primary neurons. Silencing of miR-23b resulted in reduced OGD-induced neuronal apoptosis. miR-23b inversely targeted nuclear factor erythroid 2-related factor 2 (Nrf2) and c-Myc negatively regulated miR-23b expression. Overexpression of c-Myc and inhibition of miR-23b led to reduced neurological scores of infarction area, neuronal apoptosis, shortened platform arrival time and significantly increased the time spent on the platform quadrant and the times of crossing the platform in vivo. Collectively, downregulated miR-23b by c-Myc might alleviate IBI by upregulating Nrf2.

Evaluation of monocyte-to-high-density lipoprotein cholesterol ratio and monocyte-to-lymphocyte ratio in ischemic stroke

Objectives

We aimed to evaluate the diagnostic value of the combination of the monocyte-to-high-density lipoprotein cholesterol ratio (MHR) with the monocyte-to-lymphocyte ratio (MLR) in ischemic stroke patients.

Methods

There were 253 patients who were diagnosed with ischemic stroke and 211 healthy subjects enrolled into this retrospective study.

Result

MHR and MLR were significantly higher in ischemic stroke patients compared with controls. MHR and MLR remained as independent variables for the presence of ischemic stroke. In receiver operating characteristic analyses, the optimal cut-off values for MHR and MLR were 0.28 and 0.19, respectively. The area under the curve for MHR was 0.777 (sensitivity, 66.01%; specificity, 77.25%), and that for MLR was 0.742 (sensitivity, 70.36%; specificity, 67.77%) in ischemic stroke patients. Moreover, the combination MHR and MLR increased the sensitivity compared with MHR or MLR alone.

Conclusion

The present study shows that a high MHR and MLR are each predictive for the risk of ischemic stroke, and together, they exhibit a better diagnostic value compared with each ratio alone.

Novel peripheral blood cell ratios: Effective 3-month post-mechanical thrombectomy prognostic biomarkers for acute ischemic stroke patients

BACKGROUND

Red blood cell distribution width to platelet ratio (RPR), Monocyte to high-density lipoprotein ratio (MHR), and Neutrophil to lymphocyte ratio (NLR) are novel inflammatory biomarkers in laboratory tests, which are associated with clinical outcomes in malignancy, cardiovascular and cerebrovascular diseases. This study aimed to determine their predictive value for the prognosis of acute ischemic stroke after mechanical thrombectomy (MT).

METHODS

A total of 286 patients with acute ischemic stroke (AIS) admitted to a tertiary stroke center in China between January 2018 and February 2020 were treated by MT. Demographic characteristics, risk factors, clinical data, laboratory parameters, and clinical outcomes were recorded. The clinical outcome was disability or death at discharge or 90 days (defined as a modified Rankin Scale score of 3-6). The relationship between RPR, MHR, and NLR and functional outcomes was investigated by binary Logistic regression analysis, and further assessed by receiver operating characteristic curve (ROC). The Kaplan-Meier method was used to analyze the survival rate of prognosis factors.

RESULTS

A total of 286 patients with AIS underwent MT (median age, 70.00; Interquartile range [IQR], 63.00-77.00; 41.6% female). Patients with unfavorable outcome showed higher RPR, MHR, and NLR than those with favorable outcome (RPR, [8.63; IQR, 6.30-10.78] vs [6.17; IQR, 5.11-7.35], P < 0.001; MHR, [0.40; IQR, 0.31-0.53] vs [0.34; IQR, 0.27-0.47], P = 0.005; NLR, [5.28; IQR, 3.63-8.02] vs [3.44; IQR, 2.63-4.63], P < 0.001). In multivariate and ROC curve analysis, higher RPR (>8.565) (odds ratio [OR], 1.671; 95% confidence interval [CI], 1.127-2.479; P = 0.011) and higher MHR (>0.368) (OR, 9.374; 95% CI, 1.160-75.767; P = 0.036), higher NLR (>4.030) (OR, 1.957; 95% CI, 1.382-2.770; P < 0.001) were independently associated with unfavorable outcome. The combined predictive value of the three indexes was higher than that of a single index. Kaplan-Meier survival curve analysis showed that the 90-day survival rate (82.1% vs 66.2%) was significantly different between the low RPR group and the high RPR group (χ² = 4.960, P = 0.026).

CONCLUSION

Higher RPR, MHR, and NLR might be independent risk factors for predicting 3-month poor prognosis in patients with AIS who underwent MT.

Piperine as a neuroprotective functional component in rats with cerebral ischemic injury

Long pepper (Piper longum L.) and black pepper (Piper nigrum L.) plants are commonly used as spices around the world and have also been postulated to have medicinal effects. Piperine, as the major alkaloid of P. nigrum and P. longum, has gained wide attention of the medical community and culinary enthusiasts. This study seeks to determine the effects of piperine on neuronal apoptosis in peri-infarcted cerebral cortices of rats with permanent middle cerebral artery occlusion (pMCAO) injury. Evaluation of the different behavioral components was conducted after pMCAO. 2, 3, 5-Triphenyltetrazolium chloride (TTC) was used to evaluate the area of cortical ischemia. Gross histopathological changes, as well as microscopic neuronal changes, were observed in brain tissue samples. The protein expression of Caspase-3, Caspase-9, Bax, Bcl-2, and Cytochrome C (Cyt-c) was analyzed using western blotting. The findings reveal that rats that received piperine treatment show markedly decreased neurological deficit, less ischemia-induced cellular damage, as well as smaller areas of cerebral infarction, with less severe macro and microcellular cerebral structural changes. Western blotting analysis reveals that piperine administration inhibits Bax, while enhancing Bcl-2 expression. The protein expression of Caspase-3, Caspase-9, and Cyt-c was also found to be significantly inhibited. We conclude that piperine may provide several beneficial neuroprotective effects that warrant further investigation.

N-Palmitoylethanolamide-Oxazoline Protects against Middle Cerebral Artery Occlusion Injury in Diabetic Rats by Regulating the SIRT1 Pathway

Diabetes causes various macrovascular and microvascular alterations, often culminating in major clinical complications (first of all, stroke) that lack an effective therapeutic intervention. N-palmitoylethanolamide-oxazoline (PEA-OXA) possesses anti-inflammatory and potent neuroprotective effects. Although recent studies have explained the neuroprotective properties of PEA-OXA, nothing is known about its effects in treating cerebral ischemia. Methods: Focal cerebral ischemia was induced by transient middle cerebral artery occlusion (MCAo) in the right hemisphere. Middle cerebral artery (MCA) occlusion was provided by introducing a 4–0 nylon monofilament (Ethilon; Johnson & Johnson, Somerville, NJ, USA) precoated with silicone via the external carotid artery into the internal carotid artery to occlude the MCA. Results: A neurological severity score and infarct volumes were carried out to assess the neuroprotective effects of PEA-OXA. Moreover, we observed PEA-OXA-mediated improvements in tissue histology shown by a reduction in lesion size and an improvement in apoptosis level (assessed by caspases, Bax, and Bcl-2 modulation and a TUNEL assay), which further supported the efficacy of PEA-OXA therapy. We also found that PEA-OXA treatment was able to reduce mast cell degranulation and reduce the MCAo-induced expression of NF-κB pathways, cytokines, and neurotrophic factors. Conclusions: based on these findings, we propose that PEA-OXA could be useful in decreasing the risk of impairment or improving function in ischemia/reperfusion brain injury-related disorders.

Intravenous Transplantation of Mesenchymal Stem Cells Reduces the Number of Infiltrated Ly6C+ Cells but Enhances the Proportions Positive for BDNF, TNF-1α, and IL-1β in the Infarct Cortices of dMCAO Rats

The resident microglial and infiltrating cells from peripheral circulation are involved in the pathological processes of ischemia stroke and may be regulated by mesenchymal stem/stromal cell (MSC) transplantation. The present study is aimed at differentiating the neurotrophic and inflammatory roles played by microglial vs. infiltrating circulation-derived cells in the acute phase in rat ischemic brains and explore the influences of intravenously infused allogeneic MSCs. The ischemic brain injury was induced by distal middle cerebral artery occlusion (dMCAO) in SD rats, with or without MSC infusion in the same day following dMCAO. Circulation-derived infiltrating cells in the brain were identified by Ly6C, a majority of which were monocytes/macrophages. Without MSC transplantation, among the infiltrated Ly6C⁺ cells, some were positive for BDNF, IL-1β, or TNF-α. Following MSC infusion, the overall number of Ly6C⁺ infiltrated cells was reduced by 50%. In contrast, the proportions of infiltrated Ly6C⁺ cells coexpressing BDNF, IL-1β, or TNF-α were significantly enhanced. Interestingly, Ly6C⁺ cells in the infarct area could produce either neurotrophic factor BDNF or inflammatory cytokines (IL-1β or TNF-α), but not both. This suggests that the Ly6C⁺ cells may constitute heterogeneous populations which react differentially to the microenvironments in the infarct area. The changes in cellular composition in the infarct area may have contributed to the beneficial effect of MSC transplantation.

Clearance of HBeAg and HBsAg of HBV in mice model by a recombinant HBV vaccine combined with GM-CSF and IFN-α as an effective therapeutic vaccine adjuvant

Chronic hepatitis B virus (CHB) infection is a significant public threat. Current interferon-α (IFN-α) based therapies and anti-viral drugs have failed to clear the infection in the majority of CHB patients and animal models. In our previous study, we established a combined protocol that employed a 3-day pretreatment with granulocyte-macrophage colony stimulating factor (GM-CSF) prior to a standard HBV vaccine. It achieved a 90% reduction of HBsAg level in the HBsAg transgenic mouse model. This protocol, while effective, remains too complex for clinical use. In this study, we formulated a new regimen by combining GM-CSF, IFN-α and a recombinant HBV vaccine (GM-CSF/IFN-α/VACCINE) into a single preparation and tested its efficacy in a HBV infection model. After four vaccinations, both serum HBeAg and HBsAg were cleared, accompanied by a 95% reduction of HBV⁺ hepatocytes and the presence of a large number of infiltrating CD8⁺ T cells in the liver. Mechanistically these robust responses were initiated by a vaccine-induced conversion of CCR2-dependent CD11b⁺Ly6C^hi monocytes into CD11b⁺CD11c⁺ DCs. This finding sheds light on the potential mechanism of action of the GM-CSF-based vaccine adjuvant and provides definable markers for clinical assessment during future testing of such highly potent vaccine protocols in HBV patients.

Role of the chemokine receptors CCR2 and CX3CR1 in an experimental model of thrombotic stroke

Stroke is the second cause of mortality worldwide and occurs following the interruption of cerebral blood circulation by cerebral vessel burst or subsequent to a local thrombus formation. Ischemic lesion triggers an important inflammatory response, characterized by massive infiltration of leukocytes, activation of glial cells and neurovascular reorganization. Chemokines and their receptors, such as CCR2 and CX3CR1, play an important role in leukocyte recruitment in the damaged area. Mice genetically depleted for the two receptors CCR2 and CX3CR1 underwent focal cerebral ischemia, based on the topical application of ferric chloride to truncate the distal middle cerebral artery. The infarct, limited only to the cortical area, remained stable in WT mice, while it is reduced overtime in the transgenic mice. Moreover, we did not observe any significant changes in the level of the inflammatory response in the infarcted areas while immune cell infiltration and neurovascularization are modulated according to genotype. Our results show that the genetic deletion of both CCR2 and CX3CR1 receptors has neuroprotective effects in response to a cerebral permanent ischemia. This study underlines a key role of CCR2- and CX3CR1-expressing immune cells in the neuropathology associated with ischemic injuries.

The choroid plexus is a key cerebral invasion route for T cells after stroke

Neuroinflammation contributes substantially to stroke pathophysiology. Cerebral invasion of peripheral leukocytes-particularly T cells-has been shown to be a key event promoting inflammatory tissue damage after stroke. While previous research has focused on the vascular invasion of T cells into the ischemic brain, the choroid plexus (ChP) as an alternative cerebral T-cell invasion route after stroke has not been investigated. We here report specific accumulation of T cells in the peri-infarct cortex and detection of T cells as the predominant population in the ipsilateral ChP in mice as well as in human post-stroke autopsy samples. T-cell migration from the ChP to the peri-infarct cortex was confirmed by in vivo cell tracking of photoactivated T cells. In turn, significantly less T cells invaded the ischemic brain after photothrombotic lesion of the ipsilateral ChP and in a stroke model encompassing ChP ischemia. We detected a gradient of CCR2 ligands as the potential driving force and characterized the neuroanatomical pathway for the intracerebral migration. In summary, our study demonstrates that the ChP is a key invasion route for post-stroke cerebral T-cell invasion and describes a CCR2-ligand gradient between cortex and ChP as the potential driving mechanism for this invasion route.

The potassium channel KCa3.1 constitutes a pharmacological target for astrogliosis associated with ischemia stroke

Background

Reactive astrogliosis is one of the significantly pathological features in ischemic stroke accompanied with changes in gene expression, morphology, and proliferation. KCa3.1 was involved in TGF-β-induced astrogliosis in vitro and also contributed to astrogliosis-mediated neuroinflammation in neurodegeneration disease.

Methods

Wild type mice and KCa3.1^−/− mice were subjected to permanent middle cerebral artery occlusion (pMCAO) to evaluate the infarct areas by 2,3,5-triphenyltetrazolium hydrochloride staining and neurological deficit. KCa3.1 channels expression and cell localization in the brain of pMCAO mice model were measured by immunoblotting and immunostaining. Glia activation and neuron loss was measured by immunostaining. DiBAC4 (3) and Fluo-4AM were used to measure membrane potential and cytosolic Ca²⁺ level in oxygen-glucose deprivation induced reactive astrocytes in vitro.

Results

Immunohistochemistry on pMCAO mice infarcts showed strong upregulation of KCa3.1 immunoreactivity in reactive astrogliosis. KCa3.1^−/− mice exhibited significantly smaller infarct areas on pMCAO and improved neurological deficit. Both activated gliosis and neuronal loss were attenuated in KCa3.1^−/− pMCAO mice. In the primary cultured astrocytes, the expressions of KCa3.1 and TRPV4 were increased associated with upregulation of astrogliosis marker GFAP induced by oxygen-glucose deprivation. The activation of KCa3.1 hyperpolarized membrane potential and, by promoting the driving force for calcium, induced calcium entry through TRPV4, a cation channel of the transient receptor potential family. Double-labeled staining showed that KCa3.1 and TRPV4 channels co-localized in astrocytes. Blockade of KCa3.1 or TRPV4 inhibited the phenotype switch of reactive astrogliosis.

Conclusions

Our data suggested that KCa3.1 inhibition might represent a promising therapeutic strategy for ischemia stroke.

Electronic supplementary material

The online version of this article (10.1186/s12974-017-0973-8) contains supplementary material, which is available to authorized users.

KCa3.1 Inhibition Switches the Astrocyte Phenotype during Astrogliosis Associated with Ischemic Stroke Via Endoplasmic Reticulum Stress and MAPK Signaling Pathways

Ischemic stroke is a devastating neurological disease that can initiate a phenotype switch in astrocytes. Reactive astrogliosis is a significant pathological feature of ischemic stroke and is accompanied by changes in gene expression, hypertrophied processes and proliferation. The intermediate-conductance Ca²⁺-activated potassium channel KCa3.1 has been shown to contribute to astrogliosis-induced neuroinflammation in Alzheimer’s disease (AD). We here present evidence, from both astrocytes subjected to oxygen–glucose deprivation (OGD) and from the brains of mice subjected to permanent middle cerebral artery occlusion (pMCAO), that KCa3.1 represents a valid pharmacological target for modulation of astrocyte phenotype during astrogliosis caused by ischemic stroke. In the primary cultured astrocytes, OGD led to increased expression of KCa3.1, which was associated with upregulation of the astrogliosis marker, glial fibrillary acidic protein (GFAP). Pharmacological blockade or genetic deletion of KCa3.1 suppressed OGD-induced up-regulation of GFAP, endoplasmic reticulum (ER) stress marker 78 kDa glucose-regulated protein (GRP78) and phosphorylated eIF-2α through the c-Jun/JNK and ERK1/2 signaling pathways. We next investigated the effect of genetic deletion of KCa3.1 in the pMCAO mouse model. KCa3.1 deficiency also attenuated ER stress and astrogliosis through c-Jun/JNK and ERK1/2 signaling pathways following pMCAO in KCa3.1^−/− mice. Our data suggest that blockade of KCa3.1 might represent a promising strategy for the treatment of ischemic stroke.

Enrichment of Ly6Chi monocytes by multiple GM-CSF injections with HBV vaccine contributes to viral clearance in a HBV mouse model

Adjuvants are considered a necessary component for HBV therapeutic vaccines but few are licensed in clinical practice due to concerns about safety or efficiency. In our recent study, we established that a combination protocol of 3-day pretreatments with GM-CSF before a vaccination (3 × GM-CSF+VACCINE) into the same injection site could break immune tolerance and cause over 90% reduction of HBsAg level in the HBsAg transgenic mouse model. Herein, we further investigated the therapeutic potential of the combination in AAV8–1.3HBV-infected mice. After 4 vaccinations, both serum HBeAg and HBsAg were cleared and there was a 95% reduction of HBV-positive hepatocytes, in addition to the presence of large number of infiltrating CD8⁺ T cells in the livers. Mechanistically, the HBV-specific T-cell responses were elicited via a 3 × GM-CSF+VACCINE-induced conversion of CCR2-dependent CD11b⁺ Ly6C^hi monocytes into CD11b⁺CD11c⁺ DCs. Experimental depletion of Ly6C^hi monocytes resulted in a defective HBV-specific immune response thereby abrogating HBV eradication. This vaccination strategy could lead to development of an effective therapeutic protocol against chronic HBV in infected patients.