Human albumin attenuates excessive innate immunity via inhibition of microglial Mincle/Syk signaling in subarachnoid hemorrhage

GLP-1R Agonist Liraglutide Attenuates Inflammatory Reaction and Neuronal Apoptosis and Reduces Early Brain Injury After Subarachnoid Hemorrhage in Rats

Liraglutide, one of the glucagon-like peptide 1 receptor (GLP-1R) agonists, has been demonstrated to protect brain damage produced by ischemic stroke. However, it remains unknown whether liraglutide attenuates early brain injury after subarachnoid hemorrhage. The present study was performed to explore the effect of liraglutide on early brain injury after subarachnoid hemorrhage in rats, and further investigate the potential mechanisms. Sprague-Dawley rats underwent subarachnoid hemorrhage (SAH) by endovascular perforation, then received subcutaneous injection with liraglutide (50 or 100 μg/kg) or vehicle after 2 and 12 h of SAH. SAH grading, neurological scores, brain water content, and Evans Blue extravasation were measured 24 h after SAH. Immunofluorescent staining was performed to detect the extent of microglial activation in rat brain 24 h after SAH. TUNEL staining was performed to evaluate neuronal apoptosis in rat brain of SAH. Expression of GLP-1R, cyclooxygenase-2 (COX-2), inducible nitric oxide synthase (iNOS), Bcl-2, Bax, and cleaved caspase-3 in rat brain were determined by western blot. Expression of tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) in rat brain was assessed by ELISA. Neurological dysfunction, brain water content, Evans Blue extravasation, microglial activation, and neuronal apoptosis were significantly reduced by GLP-1R agonist liraglutide. Expression of GLP-1R in rat brain was decreased after SAH, which is significantly elevated by liraglutide. Expression of inflammatory mediates like COX-2, iNOS, TNF-α, and IL-1β was increased after SAH, which were significantly inhibited by liraglutide. Furthermore, SAH caused the elevated expression of pro-apoptotic factors Bax and cleaved caspase-3 in rat brain, both of which were inhibited by liraglutide. In addition, liraglutide reversed the expression of anti-apoptotic protein Bcl-2. Our results demonstrated that liraglutide reduces early brain injury and attenuates inflammatory reaction and neuronal apoptosis in rats of SAH. Liraglutide provides neuroprotection against SAH, which might be associated with the inhibition of inflammation and apoptosis.

TSG-6 Attenuates Oxidative Stress-Induced Early Brain Injury in Subarachnoid Hemorrhage Partly by the HO-1 and Nox2 Pathways

BACKGROUND

Early brain injury (EBI) refers to acute brain injury during the first 72 h after subarachnoid hemorrhage (SAH), which is one of the major causes of poor prognosis after SAH. Here, we investigated the effect and the related mechanism of TSG-6 on EBI after SAH.

MATERIALS AND METHODS

The Sprague-Dawley rat model of SAH was developed by the endovascular perforation method. TSG-6 (5μg) was administered by an intraventricular injection within 1.5 h after SAH. The effects of TSG-6 on EBI were assessed by neurological score, brain water content (BWC) and TUNEL staining. Immunofluorescence staining was used to assay NF-κB/p-NF-κB expression in microglia. Protein expression levels of heme oxygenase-1 (HO-1), NADPH oxidase 2 (Nox2), Bcl-2, Bax, and cleaved-caspase-3 were measured to investigate the potential mechanism. The enzyme activity of superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) and the level of reactive oxygen species (ROS) were analyzed using commercially available kits.

RESULTS

The results showed that TSG-6 treatment alleviated the neurobehavioral dysfunction and reduced BWC and the number of TUNEL-positive neurons in EBI after SAH. TSG-6 decreased the ROS level and enhanced the enzyme activity of SOD and GSH-Px after SAH. Furthermore TSG-6 inhibited the NF-κB activation, increased the protein expression levels of HO-1 and Bcl-2 and decreased the expression levels of Nox2, Bax, and cleaved-caspase-3. The administration of TSG-6 siRNA abolished the protective effects of TSG-6 on EBI after SAH.

CONCLUSION

We found that TSG-6 attenuated oxidative stress and apoptosis in EBI after SAH partly by inhibiting NF-κB and activating HO-1 pathway in brain tissue.

TREM-1 Exacerbates Neuroinflammatory Injury via NLRP3 Inflammasome-Mediated Pyroptosis in Experimental Subarachnoid Hemorrhage

Neuroinflammation contributes to the pathogenesis of early brain injury induced by subarachnoid hemorrhage (SAH). Previous reports have demonstrated that triggering receptor expressed on myeloid cells 1 (TREM-1) regulates inflammatory response caused by ischemic stroke or myocardial infarction. However, whether TREM-1 could modulate neuroinflammation after SAH remains largely unknown. Here, using a mouse model of SAH, we found that the expression of TREM-1 was mainly located in microglia cells and increased to peak at 24 h following SAH. Then, TREM-1 antagonist or mimic was intranasally administrated to investigate its effect on SAH. TREM-1 inhibition with LP17 improved neurological deficits, mitigated brain water content, and preserved brain-blood barrier integrity 24 h after SAH, whereas recombinant TREM-1, a mimic of TREM-1, deteriorated these outcomes. In addition, LP17 administration restored long-term sensorimotor coordination and cognitive deficits. Pharmacological blockade of TREM-1 reduced TUNEL-positive and FJC-positive neurons, and CD68-stained microglia in ipsilateral cerebral cortex. Neutrophil invasion was inhibited as protein level of myeloperoxidase (MPO), and MPO-positive cells were both decreased. Moreover, we found that LP17 treatment ameliorated microglial pyroptosis by diminishing levels of N-terminal fragment of GSDMD (GSDMD-N) and IL-1β production. Mechanistically, both in vivo and in vitro, we depicted that TREM-1 can trigger microglial pyroptosis via activating NLRP3 inflammasome. In conclusion, our results revealed the critical role of TREM-1 in neuroinflammation following SAH, suggesting that TREM-1 inhibition might be a potential therapeutic approach for SAH.

Spliceosome-associated protein 130: a novel biomarker for idiopathic pulmonary fibrosis

Background

Spliceosome-associated protein 130 (SAP130), a novel danger-associated molecular pattern (DAMP), is involved in inflammatory disease. However, no data are available about SAP130 in idiopathic pulmonary fibrosis (IPF). Our study aimed to investigate SAP130 in the serum and lung tissue of patients with IPF and to determine its clinical significance.

Methods

SAP130 levels in the serum of 83 IPF patients and 38 healthy subjects were measured. Additionally, immunohistochemical staining for SAP130 was performed in lung specimens of IPF patients and control subjects. Correlation between serum SAP130 levels and clinical parameters were investigated.

Results

Serum SAP130 levels were elevated in IPF patients compared with healthy controls. In parallel, the expression of SAP130 in lung tissue was elevated in IPF. SAP130 levels were higher in patients with acute exacerbation of idiopathic pulmonary fibrosis (AE-IPF) than patients with stable IPF (P=0.0144). The area under curve (AUC) of the ROC curve for the diagnosis of IPF was 0.944 (95% CI, 0.810–0.997) for SAP130. The sensitivity (92.1%) and specificity (69.9%) were obtained for the cutoff value of 643.87 pg/mL. In patients with stable IPF, the SAP130 level correlated positively with fibrosis on high-resolution CT (HRCT) (r=0.4164, P=0.0029) and serum KL-6 (r=0.4564, P=0.0010), and inversely with FEV1 (r=−0.3562, P=0.0120) and DLCO (r=−0.5550, P<0.0001). In patients with AE-IPF, the SAP130 level correlated positively with fibrosis (r=0.3735, P=0.0296) and ground-glass opacity (r=0.4697, P=0.0051) on HRCT and serum Krebs von den Lungen 6 (KL-6) (r=0.5470, P= 0.0008).

Conclusions

The study suggested that SAP130 was a potential noninvasive biomarker that correlates well with disease severity of IPF. A prospective, multicentre study is required to validate the clinical and pathophysiological utility of SAP130 in IPF.

The Role of Macrophage-Inducible C-Type Lectin in Different Stages of Chronic Liver Disease

The macrophage-inducible C-type lectin (mincle) is part of the innate immune system and acts as a pattern recognition receptor for pathogen-associated molecular patterns (PAMPS) and damage-associated molecular patterns (DAMPs). Ligand binding induces mincle activation which consequently interacts with the signaling adapter Fc receptor, SYK, and NF-kappa-B. There is also evidence that mincle expressed on macrophages promotes intestinal barrier integrity. However, little is known about the role of mincle in hepatic fibrosis, especially in more advanced disease stages. Mincle expression was measured in human liver samples from cirrhotic patients and donors collected at liver transplantation and in patients undergoing bariatric surgery. Human results were confirmed in rodent models of cirrhosis and acute-on-chronic liver failure (ACLF). In these models, the role of mincle was investigated in liver samples as well as in peripheral blood monocytes (PBMC), tissues from the kidney, spleen, small intestine, and heart. Additionally, mincle activation was stimulated in experimental non-alcoholic steatohepatitis (NASH) by treatment with mincle agonist trehalose-6,6-dibehenate (TDB). In human NASH, mincle is upregulated with increased collagen production. In ApoE deficient mice fed high-fat western diet (NASH model), mincle activation significantly increases hepatic collagen production. In human cirrhosis, mincle expression is also significantly upregulated. Furthermore, mincle expression is associated with the stage of chronic liver disease. This could be confirmed in rat models of cirrhosis and ACLF. ACLF was induced by LPS injection in cirrhotic rats. While mincle expression and downstream signaling via FC receptor gamma, SYK, and NF-kappa-B are upregulated in the liver, they are downregulated in PBMCs of these rats. Although mincle expressed on macrophages might be beneficial for intestinal barrier integrity, it seems to contribute to inflammation and fibrosis once the intestinal barrier becomes leaky in advanced stages of chronic liver disease.

Programmed Cell Deaths and Potential Crosstalk With Blood-Brain Barrier Dysfunction After Hemorrhagic Stroke

Hemorrhagic stroke is a life-threatening neurological disease characterized by high mortality and morbidity. Various pathophysiological responses are initiated after blood enters the interstitial space of the brain, compressing the brain tissue and thus causing cell death. Recently, three new programmed cell deaths (PCDs), necroptosis, pyroptosis, and ferroptosis, were also found to be important contributors in the pathophysiology of hemorrhagic stroke. Additionally, blood-brain barrier (BBB) dysfunction plays a crucial role in the pathophysiology of hemorrhagic stroke. The primary insult following BBB dysfunction may disrupt the tight junctions (TJs), transporters, transcytosis, and leukocyte adhesion molecule expression, which may lead to brain edema, ionic homeostasis disruption, altered signaling, and immune infiltration, consequently causing neuronal cell death. This review article summarizes recent advances in our knowledge of the mechanisms regarding these new PCDs and reviews their contributions in hemorrhagic stroke and potential crosstalk in BBB dysfunction. Numerous studies revealed that necroptosis, pyroptosis, and ferroptosis participate in cell death after subarachnoid hemorrhage (SAH) and intracerebral hemorrhage (ICH). Endothelial dysfunction caused by these three PCDs may be the critical factor during BBB damage. Also, several signaling pathways were involved in PCDs and BBB dysfunction. These new PCDs (necroptosis, pyroptosis, ferroptosis), as well as BBB dysfunction, each play a critical role after hemorrhagic stroke. A better understanding of the interrelationship among them might provide us with better therapeutic targets for the treatment of hemorrhagic stroke.

Apelin-13/APJ system attenuates early brain injury via suppression of endoplasmic reticulum stress-associated TXNIP/NLRP3 inflammasome activation and oxidative stress in a AMPK-dependent manner after subarachnoid hemorrhage in rats

Background

Neuroinflammation and oxidative stress play important roles in early brain injury following subarachnoid hemorrhage (SAH). This study is the first to show that activation of apelin receptor (APJ) by apelin-13 could reduce endoplasmic reticulum (ER)-stress-associated inflammation and oxidative stress after SAH.

Methods

Apelin-13, apelin siRNA, APJ siRNA, and adenosine monophosphate-activated protein kinase (AMPK) inhibitor-dorsomorphin were used to investigate if the activation of APJ could provide neuroprotective effects after SAH. Brain water content, neurological functions, blood-brain barrier (BBB) integrity, and inflammatory molecules were evaluated at 24 h after SAH. Western blotting and immunofluorescence staining were applied to assess the expression of target proteins.

Results

The results showed that endogenous apelin, APJ, and p-AMPK levels were significantly increased and peaked in the brain 24 h after SAH. In addition, administration of exogenous apelin-13 significantly alleviated neurological functions, attenuated brain edema, preserved BBB integrity, and also improved long-term spatial learning and memory abilities after SAH. The underlying mechanism of the neuroprotective effects of apelin-13 is that it suppresses microglia activation, prevents ER stress from overactivation, and reduces the levels of thioredoxin-interacting protein (TXNIP), NOD-like receptor pyrin domain-containing 3 protein (NLRP3), Bip, cleaved caspase-1, IL-1β, TNFα, myeloperoxidase (MPO), and reactive oxygen species (ROS). Furthermore, the use of APJ siRNA and dorsomorphin abolished the neuroprotective effects of apelin-13 on neuroinflammation and oxidative stress.

Conclusions

Exogenous apelin-13 binding to APJ attenuates early brain injury by reducing ER stress-mediated oxidative stress and neuroinflammation, which is at least partly mediated by the AMPK/TXNIP/NLRP3 signaling pathway.

Distinct Signaling Pathways Regulate TREM2 Phagocytic and NFκB Antagonistic Activities

Several genetic variants of the Triggering Receptor Expressed on Myeloid Cells-2 (TREM2) have been shown to increase the risk of developing Alzheimer’s disease (AD) supporting a role of microglia and immune cells in the pathobiology of AD. We have employed an ectopic model of TREM2 and DAP12 expression in HEK293 cells to study selectively TREM2 dependent signaling and phagocytic functions and evaluated the effects of some of the TREM2 mutations associated with AD. We show that shedding of the TREM2 N-terminal domain does not affect the inhibition of NFκB activation induced by TREM2 while it completely blocks phagocytosis suggesting that TREM2 anti-inflammatory properties can be mediated by the TREM2 C-terminal fragment while the phagocytic activity requires the full-length receptor. In addition, we confirm in that model that apolipoprotein E (APOE) is a ligand for TREM2 and triggers TREM2 signaling. In particular, we show that APOE4 stimulates spleen tyrosine kinase (SYK) activation more potently than APOE2 in a TREM2 dependent manner. Interestingly, TREM2 appears to antagonize NFκB activation induced by phorbol ester but is unable to prevent TNFα induction of NFκB activation suggesting that TREM2 antagonizes inflammatory events triggered downstream of PKC. TREM2 mutations drastically impact TREM2 phagocytosis as well as its ability to antagonize NFκB activation and notably prevent the activation of the PI3K/AKT pathway observed with wild-type TREM2. Overall our data suggest that TREM2 dependent phagocytosis requires an activation of the SYK/PI3K/AKT/PLCγ pathways while the suppression of NFκB activation by TREM2 is independent of SYK, PI3K, and PLCγ activities. This model of ectopic TREM2-DAP12 co-expression appears suitable to study TREM2 signaling as several biological functions of TREM2 and TREM2 mutations that have been previously described in myeloid and microglial cells were also replicated in this model.

Microglial TREM-1 receptor mediates neuroinflammatory injury via interaction with SYK in experimental ischemic stroke

Neuroinflammation is initiated in response to ischemic stroke, generally with the hallmarks of microglial activation and collateral brain injury contributed by robust inflammatory effects. Triggering receptor expressed on myeloid cells (TREM)-1, an amplifier of the innate immune response, is a critical regulator of inflammation. This study identified that microglial TREM-1 expression was upregulated following cerebral ischemic injury. After pharmacologic inhibition of TREM-1 with synthetic peptide LP17, ischemia-induced infarction and neuronal injury were substantially alleviated. Moreover, blockade of TREM-1 can potentiate cellular proliferation and synaptic plasticity in hippocampus, resulting in long-term functional improvement. Microglial M1 polarization and neutrophil recruitment were remarkably abrogated as mRNA levels of M1 markers, chemokines, and protein levels of myeloperoxidase and intracellular adhesion molecule-1 (ICAM-1) were decreased by LP17. Mechanistically, both in vivo and in vitro, we delineated that TREM-1 can activate downstream pro-inflammatory pathways, CARD9/NF-κB, and NLRP3/caspase-1, through interacting with spleen tyrosine kinase (SYK). In addition, TREM-1-induced SYK initiation was responsible for microglial pyroptosis by elevating levels of gasdermin D (GSDMD), N-terminal fragment of GSDMD (GSDMD-N), and forming GSDMD pores, which can facilitate the release of intracellular inflammatory factors, in microglia. In summary, microglial TREM-1 receptor yielded post-stroke neuroinflammatory damage via associating with SYK.

Microglia-derived TNF-α mediates endothelial necroptosis aggravating blood brain-barrier disruption after ischemic stroke

Endothelium (EC) is a key component of blood–brain barrier (BBB), and has an important position in the neurovascular unit. Its dysfunction and death after cerebral ischemic/reperfusion (I/R) injury not only promote evolution of neuroinflammation and brain edema, but also increase the risk of intracerebral hemorrhage of thrombolytic therapies. However, the mechanism and specific interventions of EC death after I/R injury are poorly understood. Here we showed that necroptosis was a mechanism underlying EC death, which promoted BBB breakdown after I/R injury. Treatment of rats with receptor interacting protein kinase 1 (RIPK1)-inhibitor, necrostatin-1 reduced endothelial necroptosis and BBB leakage. We furthermore showed that perivascular M1-like microglia-induced endothelial necroptosis leading to BBB disruption requires tumor necrosis factor-α (TNF-α) secreted by M1 type microglia and its receptor, TNF receptor 1 (TNFR1), on endothelium as the primary mediators of these effects. More importantly, anti-TNFα (infliximab, a potent clinically used drug) treatment significantly ameliorate endothelial necroptosis, BBB destruction and improve stroke outcomes. Our data identify a previously unexplored role for endothelial necroptosis in BBB disruption and suggest infliximab might serve as a potential drug for stroke therapy.

Wallerian degeneration in experimental focal cortical ischemia

Wallerian degeneration (WaD), commonly secondary to cerebral infarction, is the descending damage of fiber tracts with their accompanying myelin sheaths. However, whether this sequential injury can occur in non-ischemic corpus callosum (CC) and striatum in focal cortical ischemic model has not been fully demonstrated. The present study aimed to elucidate detailed histopathologic changes in CC and striatum after acute focal cortical infarction induced by permanent distal middle cerebral artery occlusion (dMCAO) in Sprague-Dawley rat. We found that myelin integrity, myelin-related proteins, MBP and MAG, and NF200-marked neurofilaments were all compromised in non-ischemic white matter regions, bilateral CC and ipsilateral striatum, along with cortical ischemia (all P < 0.05). Electron microscopy showed wide gaps between myelin sheath layers or between axon and myelin, with an abnormal folding of myelin sheath, and enlarged fluid-filled areas. APP accumulations were noted at 24 h post-dMCAO in those non-ischemic regions, and the deposition prolonged until 14 days after cortical ischemia (all P < 0.05). Moreover, in these areas, microglia and astrocytes were robustly and persistently activated in different patterns. No substantial changes were observed in contralateral striatum. In conclusion, our results suggest that WaD may be involved in non-ischemic CC and striatum after focal cortical infarction, accompanied by APP aggregation and neuroglia initiation forming the glial scar.

Human serum albumin attenuates global cerebral ischemia/reperfusion-induced brain injury in a Wnt/β-Catenin/ROS signaling-dependent manner in rats

This study sought to clarify the role and underlying mechanisms of human serum albumin (HSA) therapy in global cerebral ischemia/reperfusion (GCI/R)-induced brain damage in rats. Five groups of adult male Wistar rats (n = 12 per group) were created as follows: sham operation (Sham), global cerebral ischemia/reperfusion (GCI/R), HSA treatment (GCI/R + HSA), Dickkopf-1 (DDK1) treatment (GCI/R + DDK1), and DDK1 plus HSA treatment (GCI/R + DKK1 + HSA). The GCI/R injury model was created using the modified Pusinelli four-vessel occlusion method. After 24 h, rats were evaluated using neurological scoring, Nissl staining, and brain tissue water content. The mRNA expression of Wnt, GSK3β, and β-Catenin in the brain were detected by quantitative real time polymerase chain reaction. The protein expression of β-Catenin and GSK-3β were investigated by western blot and immunohistochemical analysis in the presence and absence of the Wnt/β-Catenin antagonist, DKK-1. Complex I activity and ROS content were also measured. After 24 h of reperfusion, the behavior score and brain tissue water content in the GCI/R + HSA group were lower than that in the GCI/R group. In addition, the degree of neuronal injury was significantly reduced in the GCI/R + HSA group (P < 0.05). The ROS content was significantly decreased and Complex I activity was markedly raised in the GCI/R + HSA group compared to the GCI/R group (P < 0.05). Further, GSK-3β expression in the GCI/R + HSA group was lower than that in the GCI/R group, while the Wnt and β-catenin expression were increased. These effects were reversed by DKK1. Taken together, we showed that HSA attenuates GCI/R-induced brain damage and may be neuroprotective via regulation of the Wnt/β-catenin/ROS signaling pathway.

Essential roles of C-type lectin Mincle in induction of neuropathic pain in mice

Increasing evidence indicates that pattern recognition receptors (PRRs) are involved in neuropathic pain after peripheral nerve injury (PNI). While a significant number of studies support an association between neuropathic pain and the innate immune response mediated through Toll-like receptors, a family of PRRs, the roles of other types of PRRs are largely unknown. In this study, we have focused on the macrophage-inducible C-type lectin (Mincle), a PRR allocated to the C-type lectin receptor family. Here, we show that Mincle is involved in neuropathic pain after PNI. Mincle-deficient mice showed impaired PNI-induced mechanical allodynia. After PNI, expression of Mincle mRNA was rapidly increased in the injured spinal nerve. Most Mincle-expressing cells were identified as infiltrating leucocytes, although the migration of leucocytes was also observed in Mincle-deficient mice. Furthermore, Mincle-deficiency affected the induction of genes, which are reported to contribute to neuropathic pain after PNI in the dorsal root ganglia and spinal dorsal horn. These results suggest that Mincle is involved in triggering sequential processes that lead to the pathogenesis of neuropathic pain.

Mesenchymal stem cells alleviate the early brain injury of subarachnoid hemorrhage partly by suppression of Notch1-dependent neuroinflammation: involvement of Botch

BACKGROUND

Activated microglia-mediated neuroinflammation has been regarded as an underlying key player in the pathogenesis of subarachnoid hemorrhage (SAH)-induced early brain injury (EBI). The therapeutic potential of bone marrow mesenchymal stem cells (BMSCs) transplantation has been demonstrated in several brain injury models and is thought to involve modulation of the inflammatory response. The present study investigated the salutary effects of BMSCs on EBI after SAH and the potential mechanism mediated by Notch1 signaling pathway inhibition.

METHODS

The Sprague-Dawley rats SAH model was induced by endovascular perforation method. BMSCs (3 × 106 cells) were transplanted intravenously into rats, and N-[N-(3,5-difluorophenacetyl-L-alanyl)]-S-phenylglycine t-butyl ester (DAPT), a Notch1 activation inhibitor, and Notch1 small interfering RNA (siRNA) were injected intracerebroventricularly. The effects of BMSCs on EBI were assayed by neurological score, brain water content (BWC), blood-brain barrier (BBB) permeability, magnetic resonance imaging, hematoxylin and eosin staining, and Fluoro-Jade C staining. Immunofluorescence and immunohistochemistry staining, Western blotting, and quantitative real-time polymerase chain reaction were used to analyze various proteins and transcript levels. Pro-inflammatory cytokines were measured by enzyme-linked immunosorbent assay.

RESULTS

BMSCs treatment mitigated the neurobehavioral dysfunction, BWC and BBB disruption associated with EBI after SAH, reduced ionized calcium binding adapter molecule 1 and cluster of differentiation 68 staining and interleukin (IL)-1 beta, IL-6 and tumor necrosis factor alpha expression in the left hemisphere but concurrently increased IL-10 expression. DAPT or Notch1 siRNA administration reduced Notch1 signaling pathway activation following SAH, ameliorated neurobehavioral impairments, and BBB disruption; increased BWC and neuronal degeneration; and inhibited activation of microglia and production of pro-inflammatory factors. The augmentation of Notch1 signal pathway agents and phosphorylation of nuclear factor-κB after SAH were suppressed by BMSCs but the levels of Botch were upregulated in the ipsilateral hemisphere. Botch knockdown in BMSCs abrogated the protective effects of BMSCs treatment on EBI and the suppressive effects of BMSCs on Notch1 expression.

CONCLUSIONS

BMSCs treatment alleviated neurobehavioral impairments and the inflammatory response in EBI after SAH; these effects may be attributed to Botch upregulation in brain tissue, which subsequently inhibited the Notch1 signaling pathway.

Microglial Mincle receptor in the PVN contributes to sympathetic hyperactivity in acute myocardial infarction rat

Malignant ventricular arrhythmias (VAs) following myocardial infarction (MI) is a lethal complication resulting from sympathetic nerve hyperactivity. Numerous evidence have shown that inflammation within the paraventricular nucleus (PVN) participates in sympathetic hyperactivity. Our aim was to explore the role of Macrophage‐inducible C‐type lectin (Mincle) within the PVN in augmenting sympathetic activity following MI,and whether NOD‐like receptor family pyrin domain‐containing 3 (NLRP3) inflammasome/IL‐1β axis is involved in this activity. MI was induced by coronary artery ligation. Mincle expression localized in microglia within the PVN was markedly increased at 24 hours post‐MI together with sympathetic hyperactivity, as indicated by measurement of the renal sympathetic nerve activity (RSNA) and norepinephrine (NE) concentration. Mincle‐specific siRNA was administrated locally to the PVN, which consequently decreased microglial activation and sympathetic nerve activity. The MI rats exhibited a higher arrhythmia score after programmed electric stimulation than that treated with Mincle siRNA, suggesting that the inhibition of Mincle attenuated foetal ventricular arrhythmias post‐MI. The underlying mechanism of Mincle in sympathetic hyperactivity was investigated in lipopolysaccharide (LPS)‐primed naïve rats. Recombinant Sin3A‐associated protein 130kD (rSAP130), an endogenous ligand for Mincle, induced high levels of NLRP3 and mature IL‐1β protein. PVN‐targeted injection of NLRP3 siRNA or IL‐1β antagonist gevokizumab attenuated sympathetic hyperactivity. Together, the data indicated that the knockdown of Mincle in microglia within the PVN prevents VAs by attenuating sympathetic hyperactivity and ventricular susceptibility, in part by inhibiting its downstream NLRP3/IL‐1β axis following MI. Therapeutic interventions targeting Mincle signalling pathway could constitute a novel approach for preventing infarction injury.

TSG-6 attenuates inflammation-induced brain injury via modulation of microglial polarization in SAH rats through the SOCS3/STAT3 pathway

BACKGROUND

An acute and drastic inflammatory response characterized by the production of inflammatory mediators is followed by stroke, including SAH. Overactivation of microglia parallels an excessive inflammatory response and worsened brain damage. Previous studies indicate that TSG-6 has potent immunomodulatory and anti-inflammatory properties. This study aimed to evaluate the effects of TSG-6 in modulating immune reaction and microglial phenotype shift after experimental SAH.

METHODS

The SAH model was established by endovascular puncture method for Sprague-Dawley rats (weighing 280-320 g). Recombinant human protein and specific siRNAs for TSG-6 were exploited in vivo. Brain injury was assessed by neurologic scores, brain water content, and Fluoro-Jade C (FJC) staining. Microglia phenotypic status was evaluated and determined by Western immunoblotting, quantitative real-time polymerase chain reaction (qPCR) analyses, flow cytometry, and immunofluorescence labeling.

RESULTS

SAH induced significant inflammation, and M1-dominated microglia polarization increased expression of TSG-6 and neurological dysfunction in rats. rh-TSG-6 significantly ameliorated brain injury, decreased proinflammatory mediators, and skewed microglia towards a more anti-inflammatory property 24-h after SAH. While knockdown of TSG-6 further induced detrimental effects of microglia accompanied with more neurological deficits, the anti-inflammation effects of rh-TSG-6 were associated with microglia phenotypic shift by regulating the level of SOCS3/STAT3 axis.

CONCLUSIONS

TSG-6 exerted neuroprotection against SAH-induced EBI in rats, mediated in part by skewing the balance of microglial response towards a protective phenotype, thereby preventing excessive tissue damage and improving functional outcomes. Our findings revealed the role of TSG-6 in modulating microglial response partially involved in the SOCS3/STAT3 pathway and TSG-6 may be a promising therapeutic target for the treatment of brain injury following SAH.

The Mycobacterial Adjuvant Analogue TDB Attenuates Neuroinflammation via Mincle-Independent PLC-γ1/PKC/ERK Signaling and Microglial Polarization

Microglial activation has long been recognized as a hallmark of neuroinflammation. Recently, the bacillus Calmette-Guerin (BCG) vaccine has been reported to exert neuroprotective effects against several neurodegenerative disorders. Trehalose-6,6'-dibehenate (TDB) is a synthetic analogue of trehalose-6,6'-dimycolate (TDM, also known as the mycobacterial cord factor) and is a new adjuvant of tuberculosis subunit vaccine currently in clinical trials. Both TDM and TDB can activate macrophages and dendritic cells through binding to C-type lectin receptor Mincle; however, its action mechanism in microglia and their relationship with neuroinflammation are still unknown. In this article, we found that TDB inhibited LPS-induced M1 microglial polarization in primary microglia and BV-2 cells. However, TDB itself had no effects on IKK, p38, and JNK activities or cytokine expression. In contrast, TDB activated ERK1/2 through PLC-γ1/PKC signaling and in turn decreased LPS-induced NF-κB nuclear translocation. Furthermore, TDB-induced AMPK activation via PLC-γ1/calcium/CaMKKβ-dependent pathway and thereby enhanced M2 gene expressions. Interestingly, knocking out Mincle did not alter the anti-inflammatory and M2 polarization effects of TDB in microglia. Conditional media from LPS-stimulated microglial cells can induce in vitro neurotoxicity, and this action was attenuated by TDB. Using a mouse neuroinflammation model, we found that TDB suppressed LPS-induced M1 microglial activation and sickness behavior, but promoted M2 microglial polarization in both WT and Mincle^-/- mice. Taken together, our results suggest that TDB can act independently of Mincle to inhibit LPS-induced inflammatory response through PLC-γ1/PKC/ERK signaling and promote microglial polarization towards M2 phenotype via PLC-γ1/calcium/CaMKKβ/AMPK pathway. Thus, TDB may be a promising therapeutic agent for the treatment of neuroinflammatory diseases.

Flexible Signaling of Myeloid C-Type Lectin Receptors in Immunity and Inflammation

Myeloid C-type lectin receptors (CLRs) are important sensors of self and non-self that work in concert with other pattern recognition receptors (PRRs). CLRs have been previously classified based on their signaling motifs as activating or inhibitory receptors. However, specific features of the ligand binding process may result in distinct signaling through a single motif, resulting in the triggering of non-canonical pathways. In addition, CLR ligands are frequently exposed in complex structures that simultaneously bind different CLRs and other PRRs, which lead to integration of heterologous signaling among diverse receptors. Herein, we will review how sensing by myeloid CLRs and crosstalk with heterologous receptors is modulated by many factors affecting their signaling and resulting in differential outcomes for immunity and inflammation. Finding common features among those flexible responses initiated by diverse CLR-ligand partners will help to harness CLR function in immunity and inflammation.

Recombinant Netrin-1 binding UNC5B receptor attenuates neuroinflammation and brain injury via PPARγ/NFκB signaling pathway after subarachnoid hemorrhage in rats

Neuroinflammation is an essential mechanism involved in the pathogenesis of subarachnoid hemorrhage (SAH)-induced brain injury. Recently, Netrin-1 (NTN-1) is well established to exert anti-inflammatory property in non-nervous system diseases through inhibiting infiltration of neutrophil. The present study was designed to investigate the effects of NTN-1 on neuroinflammation, and the potential mechanism in a rat model of SAH. Two hundred and ninety-four male Sprague Dawley rats (weight 280-330 g) were subjected to the endovascular perforation model of SAH. Recombinant human NTN-1 (rh-NTN-1) was administered intravenously. Small interfering RNA (siRNA) of NTN-1 and UNC5B, and a selective PPARγ antagonist bisphenol A diglycidyl ether (BADGE) were applied. Post-SAH evaluations included neurobehavioral function, brain water content, Western blot analysis, and immunohistochemistry. Our results showed that endogenous NTN-1 and its receptor UNC5B level were increased after SAH. Administration of rh-NTN-1 reduced brain edema, ameliorated neurological impairments, and suppressed microglia activation after SAH, which were concomitant with PPARγ activation, inhibition of NFκB, and decrease in TNF-α, IL-6, and ICAM-1, as well as myeloperoxidase (MPO). Knockdown of endogenous NTN-1 increased expression of pro-inflammatory mediators and MPO, and aggravated neuroinflammation and brain edema. Moreover, knockdown of UNC5B using specific siRNA and inhibition of PPARγ with BADGE blocked the protective effects of rh-NTN-1. In conclusion, our findings indicated that exogenous rh-NTN-1 treatment attenuated neuroinflammation and neurological impairments through inhibiting microglia activation after SAH in rats, which is possibly mediated by UNC5B/PPARγ/NFκB signaling pathway. Exogenous NTN-1 may be a novel therapeutic agent to ameliorating early brain injury via its anti-inflammation effect.

Acupuncture through Baihui (DU20) to Qubin (GB7) mitigates neurological impairment after intracerebral hemorrhage

Inflammation plays an important role in nerve defects caused by intracerebral hemorrhage. Repairing brain damage by inhibiting the macrophage-inducible C-type lectin/spleen tyrosine kinase (Mincle/Syk) signaling pathway is a potential new target for treating cerebral hemorrhage. In this study, we aimed to determine whether acupuncture through Baihui (DU20) to Qubin (GB7) is an effective treatment for intracerebral hemorrhage through the Mincle/Syk signaling pathway. An intracerebral hemorrhage rat model was established by autologous blood infusion into the caudate nucleus. Acupuncture through Baihui to Qubin was performed for 30 minutes, once every 12 hours, for a total of three times. Piceatannol (34.62 mg/kg), a Syk inhibitor, was intraperitoneally injected as a control. Modified neurological severity score was used to assess neurological function. Brain water content was measured. Immunohistochemistry and western blot assay were used to detect immunoreactivity and protein expression levels of Mincle, Syk, and CARD9. Real-time polymerase chain reaction was used to determine interleukin-1β mRNA levels. Hematoxylin-eosin staining was performed to observe histopathological changes. Our results showed that acupuncture through Baihui to Qubin remarkably improved neurological function and brain water content, and inhibited immunoreactivity and expression of Mincle, Syk, CARD9, and interkeukin-1β. Moreover, this effect was similar to piceatannol. These findings suggest that acupuncture through Baihui to Qubin can improve neurological impairment after cerebral hemorrhage by inhibiting the Mincle/Syk signaling pathway.

Delayed Cerebral Ischemia after Subarachnoid Hemorrhage: Beyond Vasospasm and Towards a Multifactorial Pathophysiology

PURPOSE OF REVIEW

Delayed cerebral ischemia (DCI) is common after subarachnoid hemorrhage (SAH) and represents a significant cause of poor functional outcome. DCI was mainly thought to be caused by cerebral vasospasm; however, recent clinical trials have been unable to confirm this hypothesis. Studies in humans and animal models have since supported the notion of a multifactorial pathophysiology of DCI. This review summarizes some of the main mechanisms under investigation including cerebral vascular dysregulation, microthrombosis, cortical spreading depolarizations, and neuroinflammation.

RECENT FINDINGS

Recent guidelines have differentiated between DCI and angiographic vasospasm and have highlighted roles of the microvasculature, coagulation and fibrinolytic systems, cortical spreading depressions, and the contribution of the immune system to DCI. Many therapeutic interventions are underway in both preclinical and clinical studies to target these novel mechanisms as well as studies connecting these mechanisms to one another. Clinical trials to date have been largely unsuccessful at preventing or treating DCI after SAH. The only successful pharmacologic intervention is the calcium channel antagonist, nimodipine. Recent studies have provided evidence that cerebral vasospasm is not the sole contributor to DCI and that additional mechanisms may play equal if not more important roles.

The Role of Smurf1 in Neuronal Necroptosis after Lipopolysaccharide-Induced Neuroinflammation

The role of inflammation in neurological disorders such as Alzheimer's disease and Parkinson's disease is gradually recognized and leads to an urgent challenge. Smad ubiquitination regulatory factor 1 (Smurf1), one member of the HECT family, is up-regulated by proinflammatory cytokines and associated with apoptosis in acute spinal cord injury. However, the function of Smurf1 through promoting neuronal necroptosis is still limited in the central nervous system (CNS). Hence, we developed a neuroinflammatory model in adult rats following lipopolysaccharide (LPS) lateral ventral injection to elaborate whether Smurf1 is involved in necroptosis in CNS injury. The up-regulation of Smurf1 detected in the rat brain cortex was similar to the necroptotic marker RIP1 expression in a time-dependent manner after LPS-induced neuroinflammation. Meanwhile, Smurf1 knockdown with siRNA inhibited neuronal necroptosis following LPS-stimulated rat pheochromocytomal PC12 cells. Thus, it was indicated that LPS-induced necroptosis could be promoted by Smurf1. In short, these studies suggest that Smurf1 might promote neuronal necroptosis after LPS-induced neuroinflammation, which might act as a novel and potential molecular target for the treatment of neuroinflammation associated diseases.