Effect of Neuregulin on Apoptosis and Expressions of STAT3 and GFAP in Rats Following Cerebral Ischemic Reperfusion

Research progress on the mechanism of action and clinical application of remote ischemic post-conditioning for acute ischemic stroke

Remote ischemic post-conditioning (RIPostC) can reduce cerebral ischemia reperfusion injury (IRI) by inducing endogenous protective effects, the distal limb ischemia post-treatment and in situ ischemia post-treatment were classified according to the site of intervention. And in the process of clinical application distal limb ischemia post-treatment is more widely used and more conducive to clinical translation. Therefore, in this paper, we review the mechanism of action and clinical application of RIPostC in cerebral ischemia, hoping to provide reference help for future experimental directions and clinical translation.

The case for neuregulin-1 as a clinical treatment for stroke

Ischemic stroke is the leading cause of serious long-term disability and the 5th leading cause of death in the United States. Revascularization of the occluded cerebral artery, either by thrombolysis or endovascular thrombectomy, is the only effective, clinically-approved stroke therapy. Several potentially neuroprotective agents, including glutamate antagonists, anti-inflammatory compounds and free radical scavenging agents were shown to be effective neuroprotectants in preclinical animal models of brain ischemia. However, these compounds did not demonstrate efficacy in clinical trials with human patients following stroke. Proposed reasons for the translational failure include an insufficient understanding on the cellular and molecular pathophysiology of ischemic stroke, lack of alignment between preclinical and clinical studies and inappropriate design of clinical trials based on the preclinical findings. Therefore, novel neuroprotective treatments must be developed based on a clearer understanding of the complex spatiotemporal mechanisms of ischemic stroke and with proper clinical trial design based on the preclinical findings from specific animal models of stroke. We and others have demonstrated the clinical potential for neuregulin-1 (NRG-1) in preclinical stroke studies. NRG-1 significantly reduced ischemia-induced neuronal death, neuroinflammation and oxidative stress in rodent stroke models with a therapeutic window of >13 h. Clinically, NRG-1 was shown to be safe in human patients and improved cardiac function in multisite phase II studies for heart failure. This review summarizes previous stroke clinical candidates and provides evidence that NRG-1 represents a novel, safe, neuroprotective strategy that has potential therapeutic value in treating individuals after acute ischemic stroke.

Neuregulin-1 beta 1 is implicated in pathogenesis of multiple sclerosis

Multiple sclerosis is characterized by immune mediated neurodegeneration that results in progressive, life-long neurological and cognitive impairments. Yet, the endogenous mechanisms underlying multiple sclerosis pathophysiology are not fully understood. Here, we provide compelling evidence that associates dysregulation of neuregulin-1 beta 1 (Nrg-1β1) with multiple sclerosis pathogenesis and progression. In the experimental autoimmune encephalomyelitis model of multiple sclerosis, we demonstrate that Nrg-1β1 levels are abated within spinal cord lesions and peripherally in the plasma and spleen during presymptomatic, onset and progressive course of the disease. We demonstrate that plasma levels of Nrg-1β1 are also significantly reduced in individuals with early multiple sclerosis and is positively associated with progression to relapsing-remitting multiple sclerosis. The functional impact of Nrg-1β1 downregulation preceded disease onset and progression, and its systemic restoration was sufficient to delay experimental autoimmune encephalomyelitis symptoms and alleviate disease burden. Intriguingly, Nrg-1β1 therapy exhibited a desirable and extended therapeutic time window of efficacy when administered prophylactically, symptomatically, acutely or chronically. Using in vivo and in vitro assessments, we identified that Nrg-1β1 treatment mediates its beneficial effects in EAE by providing a more balanced immune response. Mechanistically, Nrg-1β1 moderated monocyte infiltration at the blood-CNS interface by attenuating chondroitin sulphate proteoglycans and MMP9. Moreover, Nrg-1β1 fostered a regulatory and reparative phenotype in macrophages, T helper type 1 (Th1) cells and microglia in the spinal cord lesions of EAE mice. Taken together, our new findings in multiple sclerosis and experimental autoimmune encephalomyelitis have uncovered a novel regulatory role for Nrg-1β1 early in the disease course and suggest its potential as a specific therapeutic target to ameliorate disease progression and severity.

Neuregulin-1β Plays a Neuroprotective Role by Inhibiting the Cdk5 Signaling Pathway after Cerebral Ischemia-Reperfusion Injury in Rats

This study investigated the effects of neuregulin-1β (NRG1β) after middle cerebral artery occlusion/reperfusion (MCAO/R) in rats to evaluate whether they occur via the cyclin-dependent kinase (Cdk)5 signaling pathway. One hundred adult male Wistar rats were randomly divided into sham, MCAO/R, treatment (NRG1β), inhibitor (roscovitine; Ros), and inhibitor + treatment (Ros + NRG1β) groups. The MCAO/R model was established using the intraluminal thread method. The neurobehavioral function was evaluated by the modified neurological severity score (mNSS). The cerebral infarction volume (CIV) was measured by triphenyl tetrazolium chloride (TTC) staining. Morphological changes were observed by hematoxylin-eosin (HE) staining. The apoptotic cell index (ACI) was detected by the terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL) assay. Immunohistochemistry and Western blotting were performed to detect the expression of calpain 1, p35/p25 (regulatory binding partners of Cdk5), Cdk5, and p-Tau in neurons. The neuronal morphology in the MCAO/R, NRG1β, Ros + NRG1β, and Ros groups differed compared to the sham group; the mNSS, CIV, ACI, and the expression of calpain 1, p35/p25, Cdk5, and p-Tau were significantly increased in all four groups (P < 0.05). In the NRG1β, Ros and Ros + NRG1β groups, the neuronal morphology was significantly improved compared to the MCAO/R group, as were the mNSS, CIV, and ACI. The levels of calpain 1, p35/p25, and p-Tau were decreased compared with the MCAO/R group (P < 0.05), while the Cdk5 expression was not significantly different (P > 0.05). NRG1β may exert neuroprotective effects by inhibiting the expression of calpain 1, p35/p25, and p-Tau after cerebral ischemia-reperfusion injury.

Transcriptomic analysis of neuregulin-1 regulated genes following ischemic stroke by computational identification of promoter binding sites: A role for the ETS-1 transcription factor

Ischemic stroke is a major cause of mortality in the United States. We previously showed that neuregulin-1 (NRG1) was neuroprotective in rat models of ischemic stroke. We used gene expression profiling to understand the early cellular and molecular mechanisms of NRG1's effects after the induction of ischemia. Ischemic stroke was induced by middle cerebral artery occlusion (MCAO). Rats were allocated to 3 groups: (1) control, (2) MCAO and (3) MCAO + NRG1. Cortical brain tissues were collected three hours following MCAO and NRG1 treatment and subjected to microarray analysis. Data and statistical analyses were performed using R/Bioconductor platform alongside Genesis, Ingenuity Pathway Analysis and Enrichr software packages. There were 2693 genes differentially regulated following ischemia and NRG1 treatment. These genes were organized by expression patterns into clusters using a K-means clustering algorithm. We further analyzed genes in clusters where ischemia altered gene expression, which was reversed by NRG1 (clusters 4 and 10). NRG1, IRS1, OPA3, and POU6F1 were central linking (node) genes in cluster 4. Conserved Transcription Factor Binding Site Finder (CONFAC) identified ETS-1 as a potential transcriptional regulator of NRG1 suppressed genes following ischemia. A transcription factor activity array showed that ETS-1 activity was increased 2-fold, 3 hours following ischemia and this activity was attenuated by NRG1. These findings reveal key early transcriptional mechanisms associated with neuroprotection by NRG1 in the ischemic penumbra.

Protective effect of hydroxysafflor yellow A alone or in combination with acetylglutamine on cerebral ischemia reperfusion injury in rat: A PET study using 18F-fuorodeoxyglucose

Hydroxysafflor yellow A (HSYA) and acetylglutamine (NAG) are extensively applied in the treatment of brain injury. In this study, we investigated the neuroprotective effect and underlying mechanism of HSYA alone or together with NAG using a rat model of cerebral ischemia reperfusion injury. Male Sprague-Dawley (SD) rats (n = 5) were intraperitoneally injected with 5, 10, 20 mg/kg HSYA, 300 mg/kg NAG and 10 mg/kg HSYA+300 mg/kg NAG after the onset of reperfusion and once each day for the following 7 days. After assessing the neurological deficit and infarct volume, we used ¹⁸F-FDG-PET to evaluate the regional cerebral metabolic rate of glucose consumption, immunohistochemical analysis to detect the expression of GFAP, NGF, Bcl-2, Bax, caspase-3 and ICAM-1 in brain tissue at day 7 after cerebral I/R injury. Meanwhile, the mRNA levels of ICAM-1, IL-1ß, TNF-α and NF-κB were determined by qRT-PCR, the protein levels of Bcl-2, Bax and caspase-3 were detected by western blot. The results indicated that HSYA significantly up-regulated glucose metabolism, improved neurological function, decreased cerebral infarction volume. HSYA alone or together with NAG attenuated apoptosis and inflammation by up-regulating GFAP, NGF and Bcl-2 expression, suppressing the expression of Bax, caspase-3 and ICAM-1, IL-1ß, TNF-α and NF-κB. These finding suggested that HSYA exerted neuroprotection against cerebral I/R injury by modulating inflammation and apoptosis process, and HSYA in combination with NAG possessed a synergetic effect on protecting cerebral I/R brain injury.

Neuregulin-1 promotes remyelination and fosters a pro-regenerative inflammatory response in focal demyelinating lesions of the spinal cord

Oligodendroglial cell death and demyelination are hallmarks of neurotrauma and multiple sclerosis that cause axonal damage and functional impairments. Remyelination remains a challenge as the ability of endogenous precursor cells for oligodendrocyte replacement is hindered in the unfavorable milieu of demyelinating conditions. Here, in a rat model of lysolecithin lysophosphatidyl-choline (LPC)-induced focal demyelination, we report that Neuregulin-1 (Nrg-1), an important factor for oligodendrocytes and myelination, is dysregulated in demyelinating lesions and its bio-availability can promote oligodendrogenesis and remyelination. We delivered recombinant human Nrg-1β1 (rhNrg-1β1) intraspinally in the vicinity of LPC demyelinating lesion in a sustained manner using poly lactic-co-glycolic acid microcarriers. Availability of Nrg-1 promoted generation and maturation of new oligodendrocytes, and accelerated endogenous remyelination by both oligodendrocyte and Schwann cell populations in demyelinating foci. Importantly, Nrg-1 enhanced myelin thickness in newly remyelinated spinal cord axons. Our complementary in vitro studies also provided direct evidence that Nrg-1 significantly promotes maturation of new oligodendrocytes and facilitates their transition to a myelinating phenotype. Nrg-1 therapy remarkably attenuated the upregulated expression chondroitin sulfate proteoglycans (CSPGs) specific glycosaminoglycans in the extracellular matrix of demyelinating foci and promoted interleukin-10 (IL-10) production by immune cells. CSPGs and IL-10 are known to negatively and positively regulate remyelination, respectively. We found that Nrg-1 effects are mediated through ErbB2 and ErbB4 receptor activation. Our work provides novel evidence that dysregulated levels of Nrg-1 in demyelinating lesions of the spinal cord pose a challenge to endogenous remyelination, and appear to be an underlying cause of myelin thinning in newly remyelinated axons.

JAK2/STAT3 pathway is involved in the protective effects of epidermal growth factor receptor activation against cerebral ischemia/reperfusion injury in rats

Cerebral ischemia and reperfusion is a common pathophysiologic process, which is involved in stroke and brain trauma. Recent studies revealed that activating epidermal growth factor receptor (EGFR) ameliorates cerebral ischemia/reperfusion (I/R) injury, however, the precise mechanisms remain to be illuminated. In this study, the neurological behavior was evaluated by Longa score. The infarct volume was performed by 2, 3, 5-triphenyltetrazolium chloride (TTC) staining and the expression of p-EGFR, p-STAT3, connexin (Cx43), Bax and Bcl-2 were detected by Western blot. The neurological behavior and infarct volume were increased in rats with cerebral I/R injury. Epidermal growth factor (EGF) pretreatment significantly decreased neurological deficit and infarct volume. However, the antagonist of EGFR, AG1478 attenuated the EGF-induced reduction of neurological deficit and infarct volume. Moreover, the inhibitor of JAK2/STAT3, AG490 undermined the protective effects stimulated by activating EGFR in rats with I/R injury. In addition, EGF pretreatment increased the expression of Bcl-2 and reduced the expression of Bax and Cx43, and the effects were abolished after using AG1478 and AG490. These findings implicate that JAK2/STAT3 pathway plays the vital role in I/R injury protection from activating EGFR. And the neuroprotective effects may associate with inhibiting the Cx43 expression and the inhibition of apoptosis.

Ursolic acid inhibits breast cancer growth by inhibiting proliferation, inducing autophagy and apoptosis, and suppressing inflammatory responses via the PI3K/AKT and NF-κB signaling pathways in vitro

Breast cancer, which is the second leading cause of cancer-associated mortality in women worldwide, develops from breast tissue. Chemotherapy is the most commonly used therapy to treat breast cancer. However, a number of natural plant-derived products have been suggested as alternative therapies to treat different types of cancer, such as breast cancer. The aim of the present study was to determine the anti-tumor effects of ursolic acid and its effect on apoptosis and inflammation in breast cancer cells. The anti-cancer effects of ursolic acid were evaluated in vitro using flow cytometry, western blotting and reverse transcription-quantitative polymerase chain reaction. The results suggest that ursolic acid inhibits the viability of breast cancer cells by inducing autophagy and apoptosis without inducing cell death. Cellular migration assays demonstrated that ursolic acid was able to suppress the invasive ability of breast cancer cells (P<0.05). In addition, the phosphoinositide 3-kinase (PI3K)/protein kinase B (AKT) pathway was downregulated following ursolic acid administration (P<0.05), leading to an upregulation of glycogen synthase kinase activity (P<0.05) and downregulation of B-cell lymphoma 2 (P<0.05), subsequently causing autophagy and apoptosis via cyclin-D1 inhibition and caspase-3 stimulation (P<0.05). Furthermore, the inflammatory response of breast cancer cells was assessed by measuring levels of nuclear factor (NF)-κB. Ursolic acid was found to downregulate NF-κB in breast cancer cells, thus inhibiting inflammation and preventing the progression of breast cancer (P<0.05). To the best of our knowledge, the present study is the first to assess the effect of ursolic acid on breast cancer cells through PI3K/AKT-regulated GSK and caspase-3 accompanied by NF-κB signaling pathways. The results of the present study regarding the potential underlying molecular mechanisms of ursolic acid may be used to develop novel therapeutic strategies for breast cancer treatment.

Neuregulin1β Effects on Brain Tissue via ERK5-Dependent MAPK Pathway in a Rat Model of Cerebral Ischemia-Reperfusion Injury

Neuregulin1β (NRG1β), a member of the excitomotor of tyrosine kinase receptor (erbB) family, was recently shown to play a neuroprotective role in cerebral ischemia-reperfusion injury. The present study analyzed the effects and its possible signaling pathway of NRG1β on brain tissues after cerebral ischemia-reperfusion injury. A focal cerebral ischemic model was established by inserting a monofilament thread to achieve middle cerebral artery occlusion, followed by an NRG1β injection via the internal carotid artery. NRG1β injection resulted in significantly improved neurobehavioral activity according to the modified neurological severity score test. Tetrazolium chloridestaining revealed a smaller cerebral infarction volume; hematoxylin-eosin staining and transmission electron microscopy showed significantly alleviated neurodegeneration in the middle cerebral artery occlusion rats. Moreover, expression of phosphorylated MEK5, phosphorylated ERK5, and phosphorylated MEK2C increased after NRG1β treatment, and the neuroprotective effect of NRG1β was attenuated by an injection of the MEK5 inhibitor, BIX02189. Results from the present study demonstrate that NRG1β provides neuroprotection following cerebral ischemia-reperfusion injury via the ERK5-dependent MAPK pathway.

Regulation of inflammatory responses by neuregulin-1 in brain ischemia and microglial cells in vitro involves the NF-kappa B pathway

Background

We previously demonstrated that neuregulin-1 (NRG-1) was neuroprotective in rats following ischemic stroke. Neuroprotection by NRG-1 was associated with the suppression of pro-inflammatory gene expression in brain tissues. Over-activation of brain microglia can induce pro-inflammatory gene expression by activation of transcriptional regulators following stroke. Here, we examined how NRG-1 transcriptionally regulates inflammatory gene expression by computational bioinformatics and in vitro using microglial cells.

Methods

To identify transcriptional regulators involved in ischemia-induced inflammatory gene expression, rats were sacrificed 24 h after middle cerebral artery occlusion (MCAO) and NRG-1 treatment. Gene expression profiles of brain tissues following ischemia and NRG-1 treatment were examined by microarray technology. The Conserved Transcription Factor-Binding Site Finder (CONFAC) bioinformatics software package was used to predict transcription factors associated with inflammatory genes induced following stroke and suppressed by NRG-1 treatment. NF-kappa B (NF-kB) was identified as a potential transcriptional regulator of NRG-1-suppressed genes following ischemia. The involvement of specific NF-kB subunits in NRG-1-mediated inflammatory responses was examined using N9 microglial cells pre-treated with NRG-1 (100 ng/ml) followed by lipopolysaccharide (LPS; 10 μg/ml) stimulation. The effects of NRG-1 on cytokine production were investigated using Luminex technology. The levels of the p65, p52, and RelB subunits of NF-kB and IkB-α were determined by western blot analysis and ELISA. Phosphorylation of IkB-α was investigated by ELISA.

Results

CONFAC identified 12 statistically over-represented transcription factor-binding sites (TFBS) in our dataset, including NF-kBP65. Using N9 microglial cells, we observed that NRG-1 significantly inhibited LPS-induced TNFα and IL-6 release. LPS increased the phosphorylation and degradation of IkB-α which was blocked by NRG-1. NRG-1 also prevented the nuclear translocation of the NF-kB p65 subunit following LPS administration. However, NRG-1 increased production of the neuroprotective cytokine granulocyte colony-stimulating factor (G-CSF) and the nuclear translocation of the NF-kB p52 subunit, which is associated with the induction of anti-apoptotic and suppression of pro-inflammatory gene expression.

Conclusions

Neuroprotective and anti-inflammatory effects of NRG-1 are associated with the differential regulation of NF-kB signaling pathways in microglia. Taken together, these findings suggest that NRG-1 may be a potential therapeutic treatment for treating stroke and other neuroinflammatory disorders.

Carnosic acid nanoparticles suppress liver ischemia/reperfusion injury by inhibition of ROS, Caspases and NF-κB signaling pathway in mice

Living donor liver transplantation (LDLT) requires ischemia/reperfusion (I/R), which can lead to early graft injury. However, the detailed molecular mechanism of I/R injury remains unclear. Carnosic acid, as a phenolic diterpene with function of anti-inflammation, anti-cancer, anti-bacterial, anti-diabetic, as well as neuroprotective properties, is produced by many species from Lamiaceae family. Nanoparticulate drug delivery systems have been known to better the bioavailability of drugs on intranasal administration compared with only drug solutions. Administration of carnosic acid nanoparticles was thought to be sufficient to lead to considerable inhibition of liver injury progression induced by ischemia/reperfusion. In our study, liver ischemia/reperfusion injury was established successfully with C57BL/6 animal model. 10 and 20mg/kg carnosic acid nanoparticles were injected to mice for five days prior to ischemia. After liver ischemia/reperfusion, the levels of serum AST, ALT and APL were increased, which was attenuated by pre-treatment with carnosic acid nanoparticles. In addition, carnosic acid nanoparticles inhibited ROS production via its related signals regulation. And carnosic acid nanoparticles also suppressed the ischemia/reperfusion-induced up-regulation in the pro-apoptotic protein and mRNA levels of Bax, Cyto-c, Apaf-1 and Caspase-9/3 while increased ischemia/reperfusion-induced decrease of anti-apoptotic factor of Bcl-2. Further, ischemia/reperfusion-induced inflammation was also inhibited for carnosic acid nanoparticles administration via inactivating NF-κB signaling pathway, leading to down-regulation of pro-inflammatory cytokines releasing. In conclusion, our study suggested that carnosic acid nanoparticles protected against liver ischemia/reperfusion injury via its role of anti-oxidative, anti-apoptotic and anti-inflammatory bioactivity.

Propofol Suppressed Hypoxia/Reoxygenation-Induced Apoptosis in HBVSMC by Regulation of the Expression of Bcl-2, Bax, Caspase3, Kir6.1, and p-JNK

Recent studies have found that propofol may protect brain from cerebral ischemic-reperfusion injury. However, the underlying mechanism remains unclear. The effects of propofol were evaluated in HBVSMC after hypoxia/reoxygenation (H/R). Cell viability and levels of SOD, LDH, and MDA were measured. Apoptosis was detected by flow cytometry. The levels of Bax, Bcl-2, Caspase3, Sur2b, Kir6.1, JNK, p-JNK, mTOR, and p-mTOR proteins were measured by western blotting. H/R decreased cell viability and SOD activity and increased LDH leakage and MDA content in HBVSMC, all of which were significantly reversed by propofol. Propofol suppressed the levels of H/R-induced apoptosis. The expression of Bcl-2 and p-mTOR was significantly downregulated and the expression levels of Bax, Caspase3, Kir6.1, and p-JNK were upregulated following H/R injury. The ratio of p-JNK/JNK was increased; however, that of p-mTOR/mTOR decreased correspondingly. The effects on the expression of these proteins were reversed by propofol treatment. SP600125 enhanced and Everolimus attenuated the effect of propofol. These findings suggested that the protective effect of propofol against H/R injury in the HBVSMC was through the inhibition of apoptosis by inducing the expression of Bcl-2 and p-mTOR as well as inhibiting the expression levels of Bax, Caspase3, Kir6.1, and p-JNK.

Neuregulin1β improves cognitive dysfunction and up-regulates expression of p-ERK1/2 in rats with chronic omethoate poisoning

Objective

To observe the effects of neuregulin1β (NRG1β) on the level of phosphorylated ERK1/2 (p-ERK1/2), and explore the therapeutic mechanism of NRG1β on the cognitive dysfunction in rats with chronic omethoate poisoning.

Methods

Rats with strong learning and memory ability, 50 in total, were selected by Y-electric maze test. Among which, 15 rats were randomly selected into control group, and the rest 35 rats were used to establish experimental cognitive impairment models by being injected with omethoate subcutaneously. The 30 cases of successful cognitive impairment models were randomly divided into model group and treated group consisting of 15 rats, respectively. Then rats in treated group were injected with NRG1β into their lateral ventricles, while rats in control and model groups were given equal volume of PBS simultaneously. The cognitive capacity of rats was evaluated with Y-electric maze. The morphology and ultrastructure of hippocampus were observed by hematoxylin eosin (HE) staining and transmission electron microscopy (TEM) respectively. The expression of p-ERK1/2 was determined by immunohistochemical (IHC) staining and Western blotting.

Results

Compared with rats in model group, the cognitive ability of rats with omethoate exposed (model and treated groups) reduced significantly, along with the obvious damage of hippocampal neurons and the expression of p-ERK1/2 decreased significantly (P < 0.05). And after treatment with NRG1β, the cognitive activity of treated rats was improved obviously, and the injury of hippocampal neurons was milder and the expression of p-ERK1/2 increased significantly more than those in model rats (P < 0.05).

Conclusion

In chronic omethoate poisoning rats, NRG1β can promote the phosphorylation level of ERK1/2 in hippocampal neurons, and play an important role in the improvement of cognitive function.

Endogenous protection derived from activin A/Smads transduction loop stimulated via ischemic injury in PC12 cells

Activin A (ActA), a member of transforming growth factor-beta (TGF-b) super- family, affects many cellular processes, including ischemic stroke. Though the neuroprotective effects of exogenous ActA on oxygen-glucose deprivation (OGD) injury have already been reported by us, the endogenous role of ActA remains poorly understood. To further define the role and mechanism of endogenous ActA and its signaling in response to acute ischemic damage, we used an OGD model in PC12 cells to simulate ischemic injury on neurons in vitro. Cells were pre-treated by monoclonal antibody against activin receptor type IIA (ActRII-Ab). We found that ActRII-Ab augments ischemic injury in PC12 cells. Further, the extracellular secretion of ActA as well as phosphorylation of smad3 in PC12 cells was also up-regulated by OGD, but suppressed by ActRII-Ab. Taken together, our results show that ActRII-Ab may augment ischemic injury via blocking of transmembrane signal transduction of ActA, which confirmed the existence of endogenous neuroprotective effects derived from the ActA/Smads pathway. ActRIIA plays an important role in transferring neuronal protective signals inside. It is highly possible that ActA transmembrance signaling is a part of the positive feed-back loop for extracellular ActA secretion.

Effects of apoptosis-related proteins caspase-3, Bax and Bcl-2 on cerebral ischemia rats

Neuron apoptosis is known to mediate a change of ethology following cerebral ischemia-reperfusion injury in rats. Additionally, Bcl-2, Bax and caspase-3 proteins may exert a significant effect on neuron injury. The aim of this study was to investigate the role, mechanism of action and clinical significance of these proteins in neuron apoptosis and functional impairment following cerebral ischemia-reperfusion injury in rats. Sixty male healthy adult Wistar rats were randomly assigned into control (n=6), sham operation (n=6) and experimental (n=48) groups. The model of rat cerebral ischemia-reperfusion injury was set up according to the method of Zea-Longa. Eight subsets of 6 rats-subset were designed according to time points (at 3, 6, 12, 24 and 48 h and at 3, 7 and 14 days). Nerve functional injury was evaluated and graded using nerve function score, balance, coordination function detection and measurement of forelimb placing. The neurons expressing caspase-3, Bax and Bcl-2 in the cortical area, CA3, CA1, stratum lucidum (Slu) and molecular layer of the dentate gyrus (MoDG) of the hippocampus were detected using immunohistochemistry or the TUNEL method. The expression of caspase-3, Bax and Bcl-2 genes was detected by the reverse transcriptase polymerase chain reaction (RT-PCR). The results indicated that, compared to the sham operation group, the score of nerve function and balance beam walking were distinctly higher (P<0.01) and the percentage of rat foreleg touching the angle or margin of the table was significantly lower in the experimental rat group (P<0.01) at 3 h following reperfusion. The expression of TUNEL-positive neurons was high in the cortical area and the CA3 region of the hippocampus (P<0.01), caspase-3 was at peak value in the cortical area and the CA1 region of the hippocampus (P<0.01), Bax was increased in the cortical area and the Slu of the hippocampus (P<0.01) and Bcl-2 was low in the cortical area and the MoDG of the hippocampus (P<0.01) in the experimental group at 48 h following reperfusion. In conclusion, cerebral ischemia/reperfusion injury may cause neurological impairment and lead to a change of ethology, and neuron apoptosis may be associated with the activation of caspase-3 and Bax and the downregulation of Bcl-2.

Neuregulin-1β regulates tyrosine kinase receptor expression in cultured dorsal root ganglion neurons with excitotoxicity induced by glutamate

Neuregulin-1 (NRG-1) signaling regulates neuronal development, migration, myelination, and synaptic maintenance. Three members of tyrosine kinase receptor (Trk) family, TrkA, TrkB, and TrkC, have been identified in DRG neurons. Whether NRG-1β and its signaling pathways influence the expression of these Trk receptors in DRG neurons is still unclear. In the present study, primary cultured DRG neurons were used to determine the effects of NRG-1β on TrkA, TrkB, and TrkC expression in DRG neurons with excitotoxicity induced by glutamate (Glu). The involvement of phosphatidylinositol 3-kinase (PI3K)/Akt and the effects of extracellular signal-regulated protein kinase (ERK1/2) signaling pathways on NRG-1β were also determined. DRG neurons were cultured for 48h and then exposed to Glu, Glu plus NRG-1β, LY294002 plus Glu plus NRG-1β, PD98059 plus Glu plus NRG-1β, and PD98059 plus LY294002 plus Glu plus NRG-1β for an additional 24h. The DRG neurons were continuously exposed to culture media as a control. After that, all cultures were processed for detection of mRNA levels of TrkA, TrkB, and TrkC using real time-PCR analysis. Protein levels of TrkA, TrkB, and TrkC were detected using a Western blot assay. The expression of TrkA, TrkB, and TrkC in situ was determined by a fluorescent labeling technique. The levels of phosphorylated Akt (pAkt), phosphorylated ERK1/2 (pERK1/2), total protein levels of Akt and ERK1/2 were detected using a Western blot assay. The results indicated that in primary cultured DRG neurons with excitotoxicity induced by Glu, NRG-1β increased the expression of TrkA and TrkB their mRNAs, but not TrkC and its mRNA. Inhibitors (LY294002, PD98059) either alone or in combination blocked the effects of NRG-1β. NRG-1β may play an important role in regulating the expression of different Trk receptors in DRG neurons through the PI3K/Akt and ERK1/2 signaling pathways.

Protective effect of carbamazepine on kainic acid-induced neuronal cell death through activation of signal transducer and activator of transcription-3

Studies have shown that the protective effect of carbamazepine (CBZ) on seizure-induced neuronal injury. However, its precise mechanisms remain unknown. Here, to investigate the neuroprotective mechanism of CBZ against seizure-induced neuronal cell death, we identified the change of gene expressions by CBZ in the hippocampus of kainic acid (KA)-treated mice using microarray method, and studied the involvement of candidate gene in neuroprotective action of CBZ. KA (15 mg/kg) and/or CBZ (30 mg/kg, 0.5 h after KA exposure) were injected intraperitoneally into mice. Through microarray analysis, we found that signal transducer and activator of transcription-3 (Stat3) gene expression was upregulated in the hippocampal CA3 region, 24 h after KA injection (15 mg/kg), and that CBZ further elevated Stat3 expression in KA-treated mice. KA also increased the protein level and phosphorylation of Stat3, and CBZ further increased the Stat3 phosphorylation, without changing Stat3 protein level in KA-treated mice. In particular, phospho-Stat3 immunoreactivity (IR) by KA was shown in astrocytes rather than in neurons; whereas phospho-Stat3 IR by CBZ in KA-treated mice was observed predominantly in neurons, and also in neuroprotective protein Bcl-xL-expression cells. These results indicate that Stat3 may play an important role in neuroprotective action of CBZ on seizure-induced neuronal injury.

Leptin administration alleviates ischemic brain injury in mice by reducing oxidative stress and subsequent neuronal apoptosis

BACKGROUND

Recent research has indicates that leptin plays a protective role in traumatic brain injury. We studied the protective effect of leptin on cerebral ischemia/reperfusion injury by using mice transient focal cerebral ischemia/reperfusion injury model.

METHODS

The distribution of 125I-leptin in the mouse brain was assessed by radioimmunoassay method. Mouse models of transient focal cerebral ischemia were established by occlusion of the right middle cerebral artery for two hours followed by 24 hours reperfusion. The neurologic deficits and infarct volume were determined using the Longa's score and 2,3,5-triphenyltetrazolium chloride staining, respectively. Regional cerebral blood flow was monitored by a laser-Doppler blood flowmeter. The levels of malondialdehyde, nitric oxide, nitric oxide synthase, and superoxide dismutase were detected according to respective assay kit. The histologic changes and neuronal apoptosis were observed with hematoxylin and eosin and transferase-mediated dUTP-biotin nick end labeling staining, respectively. The expression of B-cell lymphoma/leukemia-2 (Bcl-2) and cysteineasparateprotease-3 (caspase-3) were investigated by Western blot and real-time polymerase chain reaction assay.

RESULTS

Leptin decreased infarct volume and neurologic defects and improved regional cerebral blood flow and microvascular branch blood flow after injury. The malondialdehyde and nitric oxide levels were reduced, and superoxide dismutase level was increased after leptin treatment, which also minimized histologic changes and neuronal apoptosis, led to the upregulation of Bcl-2 and downregulation of caspase-3 expression after injury.

CONCLUSIONS

Peripherally administered leptin crossed the blood-brain barrier and was distributed into multiple regions of the brain; in the brain, leptin directly alleviated the injury-evoked damages by reducing oxidative stress and neuronal apoptosis.

Neuregulin-1 is neuroprotective in a rat model of organophosphate-induced delayed neuronal injury

Current medical countermeasures against organophosphate (OP) nerve agents are effective in reducing mortality, but do not sufficiently protect the CNS from delayed brain damage and persistent neurological symptoms. In this study, we examined the efficacy of neuregulin-1 (NRG-1) in protecting against delayed neuronal cell death following acute intoxication with the OP diisopropylflurophosphate (DFP). Adult male Sprague-Dawley rats were pretreated with pyridostigmine (0.1 mg/kg BW, i.m.) and atropine methylnitrate (20 mg/kg BW, i.m.) prior to DFP (9 mg/kg BW, i.p.) intoxication to increase survival and reduce peripheral signs of cholinergic toxicity but not prevent DFP-induced seizures or delayed neuronal injury. Pretreatment with NRG-1 did not protect against seizures in rats exposed to DFP. However, neuronal injury was significantly reduced in most brain regions by pretreatment with NRG-1 isoforms NRG-EGF (3.2 μg/kg BW, i.a) or NRG-GGF2 (48 μg/kg BW, i.a.) as determined by FluroJade-B labeling in multiple brain regions at 24 h post-DFP injection. NRG-1 also blocked apoptosis and oxidative stress-mediated protein damage in the brains of DFP-intoxicated rats. Administration of NRG-1 at 1h after DFP injection similarly provided significant neuroprotection against delayed neuronal injury. These findings identify NRG-1 as a promising adjuvant therapy to current medical countermeasures for enhancing neuroprotection against acute OP intoxication.

Aspirin upregulates the expression of neuregulin 1 and survivin after focal cerebral ischemia/reperfusion in rats

Neuregulin 1 (NGR1) and survivin have been shown to be neuroprotective. However, the link between their expression and aspirin in the treatment of cerebral ischemia remains unclear. Here, we investigated the effect of aspirin on NGR1 and survivin expression after focal cerebral ischemia/reperfusion in rats. Sprague Dawley rats were randomly divided into an aspirin treatment group (n=40) and a control group (n=40). Each group was further divided into five subgroups according to the time after reperfusion. A middle cerebral artery model was established by an occlusion suture. At 24 h, 3, 5 and 7 days after reperfusion, the Bederson neurological deficit scores were 1.47±0.11, 1.22±0.08, 0.85±0.15 and 0.59±0.12 in the treatment group, and 1.87±0.18, 1.45±0.14, 1.05±0.08 and 0.75±0.15 in the control group, respectively, indicating a significant difference at each time point (P<0.05). In the infarct center, the number of NGR1- and survivin-positive cells reached the maximum at 6 h and decreased gradually to a minimum at 7 days, while in the peri-infarct area, the number was few at 6 h, peaked at 3 days and then was reduced gradually with significant differences between the two time points (P<0.05). There were more NGR1- and survivin-positive cells in the treatment group compared to the control group (P<0.05). In conclusion, the neuroprotective effect of aspirin is at least partly mediated by the upregulation of NGR1 and survivin expression after ischemia.

Activation of signal transducer and activator of transcription-3 by a peroxisome proliferator-activated receptor gamma agonist contributes to neuroprotection in the peri-infarct region after ischemia in oophorectomized rats

BACKGROUND AND PURPOSE

The role of the phosphorylated signal transducer and activator of transcription-3 (p-STAT3) after cerebral ischemia by the peroxisome proliferator-activated receptor γ (PPARγ) agonist pioglitazone (PGZ) remains controversial. Whether the increase in p-STAT3 by estrogen is mediated by the estrogen receptor α is also obscure. We examined the role of p-STAT3, PPARγ, and estrogen receptor α against ischemic brain damage after PGZ treatment.

METHODS

Female Wistar rats subjected or not subjected to bilateral oophorectomy were injected with 1.0 or 2.5 mg/kg PGZ 2 days, 1 day, and 1 hour before 90-minute middle cerebral artery occlusion-reperfusion and compared with vehicle-control rats.

RESULTS

The cortical infarct size was larger in ovariectomized than in nonovarietomized rats; it was reduced by PGZ treatment. Inversely with the reduction of the infarct size, PPARγ, and p-STAT3 but not estrogen receptor α in the peri-infarct area were increased in PGZ-treated compared with vehicle-control rats. The increase in PPARγ and p-STAT3 was associated with the transactivation of antiapoptotic and survival genes and the reduction of caspase-3 in this area. Inhibitors of PPARγ or STAT3 abolished the PGZ-induced neuroprotection and the increase in p-STAT3. More importantly, p-STAT3 increased by PGZ was bound to PPARγ and the complex translocated to the nucleus to dock to the response element through p-STAT3.

CONCLUSIONS

Our findings suggest that the activation in the peri-infarct region of p-STAT3 and PPARγ by PGZ is essential for neuroprotection after ischemia and that PGZ may be of benefit even in postmenopausal stroke patients.