Neuroprotection by neuregulin-1 in a rat model of permanent focal cerebral ischemia

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.

ErbB4 processing is involved in OGD/R induced neuron injury

OBJECTIVE

Our previous study found that ErbB4 gene expression was changed after oxygen-glucose deprivation/reperfusion (OGD/R). However, the exact role and mechanism of ErbB4 in brain ischemia are largely unknown. In this study, we explored the protective effects of ErbB4 and its possible mechanism after OGD/R.

METHODS

Cerebral ischemia/reperfusion (I/R) injury model was established in vitro and in vivo. Cell viability, apoptosis, and ROS production were measured by MTT, TUNEL, and fluorescent probe 2', 7'-dichlorofluorescein diacetate (DCFH-DA). Infarct size was evaluated by TTC. We performed bioinformatics analyses to screen for novel key genes involved in ErbB4 changes. RNA-Seq was used to transcriptome analysis. RNA and protein expression were detected by quantitative RT‒PCR and western bloting.

RESULTS

The expression of 80-kDa ErbB4 decreased after cerebral I/R injury in vitro and in vivo. Co-expression network analysis revealed that ErbB4 expression was correlated with the changes in Adrb1, Adrb2, Ldlr, and Dab2. Quantitative RT‒PCR revealed that the mRNA expression levels of Adrb1, Adrb2, and Dab2 were upregulated, and that of Ldlr was decreased after OGD/R. Activation of ErbB4 expression by neuregulin 1 (NRG1) significantly promoted cell survival, attenuated hippocampal apoptosis, and decreased ROS production after OGD/R. Furthermore, the elimination of ErbB4 using a specific siRNA reversed these beneficial effects.

CONCLUSION

Our data revealed the neuroprotective effects of ErbB4 against OGD/R injury, and the action could be related to changes in the ErbB4 membrane-associated fragment and the expression of Adrb1, Adrb2, Ldlr, and Dab2.

Effect of thymosin β4 on lipopolysaccharide‑stimulated brain microvascular endothelial cell remodeling: A possible role in blood‑brain barrier injury

War veterans, in particular, are more prone to mental illness as they are more likely to have encountered multiple traumatic brain injuries (TBIs) whilst serving on active duty in war zone areas. A TBI is known to cause mortality or serious neurological disabilities among survivors and elicits a number of pathological processes, including neuroinflammation and blood brain barrier (BBB) disruption, leading to secondary brain damage and subsequent impairment of the neurovascular unit. Although several drugs exhibit promising effects for TBI, the repertoire of currently available therapeutic strategies remains limited. Thymosin 4 (Tβ4) is a 43-amino acid G-acting sequestering peptide that confers neuroprotective potential in TBI models. However, its role in BBB function remains unclear. Further research into the mechanism of BBB disruption induced by TBI and its specific role in neurovascular pathophysiology is necessary. In the present study, the protective effects of Tβ4 in lipopolysaccharide (LPS)-stimulated gene expression of several tight junction proteins, inflammatory genes, apoptotic genes, and adhesion genes in human brain microvascular endothelial cells (hBMVECs), one of the pivotal cell types in the BBB, were reported. The results suggested that pretreatment with Tβ4 reversed the LPS-induced damage of BBB components in hBMVECs. Furthermore, these results identified neuregulin 1 as a possible target for Tβ4. Therefore, it is proposed that Tβ4-mediated cellular signaling in hBMVEC may be vital for understanding the association between the BBB and TBI pathophysiology, which warrants further investigation.

The NG2-glia is a potential target to maintain the integrity of neurovascular unit after acute ischemic stroke

The neurovascular unit (NVU) plays a critical role in health and disease. In the current review, we discuss the critical role of a class of neural/glial antigen 2 (NG2)-expressing glial cells (NG2-glia) in regulating NVU after acute ischemic stroke (AIS). We first introduce the role of NG2-glia in the formation of NVU during development as well as aging-induced damage to NVU and accompanying NG2-glia change. We then discuss the reciprocal interactions between NG2-glia and the other component cells of NVU, emphasizing the factors that could influence NG2-glia. Damage to the NVU integrity is the pathological basis of edema and hemorrhagic transformation, the most dreaded complication after AIS. The role of NG2-glia in AIS-induced NVU damage and the effect of NG2-glia transplantation on AIS-induced NVU damage are summarized. We next discuss the role of NG2-glia and the effect of NG2-glia transplantation in oligodendrogenesis and white matter repair as well as angiogenesis which is associated with the outcome of the patients after AIS. Finally, we review the current strategies to promote NG2-glia proliferation and differentiation and propose to use the dental pulp stem cells (DPSC)-derived exosome as a promising strategy to reduce AIS-induced injury and promote repair through maintaining the integrity of NVU by regulating endogenous NG2-glia proliferation and differentiation.

Neuregulin-1 reverses anxiety-like behavior and social behavior deficits induced by unilateral micro-injection of CoCl2 into the ventral hippocampus (vHPC)

Neuregulin-1 (NRG1) is an epidermal growth factor family member with essential roles in the developing and adult nervous systems. In recent years, establishing evidence has collectively suggested that NRG1 is a new modulator of central nervous system (CNS) injury and disease, with multifaceted roles in neuroprotection, remyelination, neuroinflammation, and other repair mechanisms. NRG1 signaling exerts its effects via the tyrosine kinase receptors ErbB2-ErbB4. The NRG1/ErbB network in CNS pathology and repair has evolved, primarily in recent years. In the present study, we demonstrated that a unilateral microinjection of CoCl₂ into the ventral hippocampus (vHPC) induced hypoxic insult and led to anxiety-related behaviors and deficit sociability in mice. NRG1 treatment significantly alleviated the CoCl₂-induced increase of hypoxic-related molecules and behavioral abnormalities. Furthermore, NRG1 reduced the CoCl₂-induced neuroinflammation and neuronal deficits in the vHPC or primary hippocampal neurons in mice. Collectively, these results suggest that NRG1 ameliorates hypoxia by alleviating synaptic deficits and behavioral abnormalities of the CoCl₂-induced vHPC hypoxic model.

Astragaloside VI Ameliorates Post-Stroke Depression via Upregulating the NRG-1-Mediated MEK/ERK Pathway

BACKGROUND

Post-stroke depression (PSD) has been identified as one of the most commonly occurring complications attributed to stroke. Astragaloside VI (AsVI), which is an active Radix Astragali (AR)-derived compound, has been reported to be a potential drug for post-stroke therapy, but its effects on PSD and the underlying mechanisms remain uncovered.

METHODS

In this study, healthy male SD rats underwent a middle cerebral artery occlusion (MCAO) stroke model. To create a PSD model, these rats were then kept in isolated houses and subjected to chronic unpredictable mild stress. The rats were examined every five days for a series of behavioral tests of depression. The antidepressant properties of AsVI were also investigated in vitro in a corticosterone (CORT)-induced major depression model using a CCK-8 assay. The release of neurotransmitters dopamine (DA)/5-hydroxytryptamine (5-HT) was measured using HPLC. The expression of the neurotrophic factor Neuregulin 1 (NRG-1) in rat brain tissues was detected by immunostaining. The protein expression of NRG-1, p-MEK1, and p-ERK1/2 was analyzed utilizing western blotting.

RESULTS

AsVI treatment significantly reduced depression-like behaviors in PSD rats and attenuated the CORT-induced apoptotic cell death in neuronal PC-12 cells. Besides, AsVI treatment remarkably prevented the decrease of the levels of DA and 5-HT in the PSD rat brains and in CORT-induced PC-12 cells. Furthermore, AsVI treatment upregulated the NRG-1-mediated MEK/ERK pathway, which is associated with the improvement of PSD.

CONCLUSIONS

These findings suggest that AsVI could improve PSD at least partially by upregulating NRG-1-mediated MEK/ERK pathway. AsVI could be a novel therapeutic option for treating PSD.

Availability of neuregulin-1beta1 protects neurons in spinal cord injury and against glutamate toxicity through caspase dependent and independent mechanisms

Spinal cord injury (SCI) causes sensorimotor and autonomic impairment that partly reflects extensive, permanent loss of neurons at the epicenter and penumbra of the injury. Strategies aimed at enhancing neuronal protection are critical to attenuate neurodegeneration and improve neurological recovery after SCI. In rat SCI, we previously uncovered that the tissue levels of neuregulin-1beta 1 (Nrg-1β1) are acutely and persistently downregulated in the injured spinal cord. Nrg-1β1 is well-known for its critical roles in the development, maintenance and physiology of neurons and glia in the developing and adult spinal cord. However, despite this pivotal role, Nrg-1β1 specific effects and mechanisms of action on neuronal injury remain largely unknown in SCI. In the present study, using a clinically-relevant model of compressive/contusive SCI in rats and an in vitro model of glutamate toxicity in primary neurons, we demonstrate Nrg-1β1 provides early neuroprotection through attenuation of reactive oxygen species, lipid peroxidation, necrosis and apoptosis in acute and subacute stages of SCI. Mechanistically, availability of Nrg-1β1 following glutamate challenge protects neurons from caspase-dependent and independent cell death that is mediated by modulation of mitochondria associated apoptotic cascades and MAP kinase and AKT signaling pathways. Altogether, our work provides novel insights into the role and mechanisms of Nrg-1β1 in neuronal injury after SCI and introduces its potential as a new neuroprotective target for this debilitating neurological condition.

Neuregulins in Neurodegenerative Diseases

Neurodegenerative diseases, including Alzheimer's disease (AD), Parkinson's disease (PD) and amyotrophic lateral sclerosis (ALS), are typically characterized by progressive neuronal loss and neurological dysfunctions in the nervous system, affecting both memory and motor functions. Neuregulins (NRGs) belong to the epidermal growth factor (EGF)-like family of extracellular ligands and they play an important role in the development, maintenance, and repair of both the central nervous system (CNS) and peripheral nervous system (PNS) through the ErbB signaling pathway. They also regulate multiple intercellular signal transduction and participate in a wide range of biological processes, such as differentiation, migration, and myelination. In this review article, we summarized research on the changes and roles of NRGs in neurodegenerative diseases, especially in AD. We elaborated on the structural features of each NRG subtype and roles of NRG/ErbB signaling networks in neurodegenerative diseases. We also discussed the therapeutic potential of NRGs in the symptom remission of neurodegenerative diseases, which may offer hope for advancing related treatment.

Therapeutic Role of Neuregulin 1 Type III in SOD1-Linked Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a devastating motoneuron (Mn) disease without effective cure currently available. Death of MNs in ALS is preceded by failure of neuromuscular junctions and axonal retraction. Neuregulin 1 (NRG1) is a neurotrophic factor highly expressed in MNs and neuromuscular junctions that support axonal and neuromuscular development and maintenance. NRG1 and its ErbB receptors are involved in ALS. Reduced NRG1 expression has been found in ALS patients and in the ALS SOD1G93A mouse model; however, the expression of the isoforms of NRG1 and its receptors is still controversial. Due to the reduced levels of NRG1 type III (NRG1-III) in the spinal cord of ALS patients, we used gene therapy based on intrathecal administration of adeno-associated virus to overexpress NRG1-III in SOD1G93A mice. The mice were evaluated from 9 to 16 weeks of age by electrophysiology and rotarod tests. At 16 weeks, samples were harvested for histological and molecular analyses. Our results indicate that overexpression of NRG1-III is able to preserve neuromuscular function of the hindlimbs, improve locomotor performance, increase the number of surviving MNs, and reduce glial reactivity in the treated female SOD1G93A mice. Furthermore, the NRG1-III/ErbB4 axis appears to regulate MN excitability by modulating the chloride transporter KCC2 and reduces the expression of the MN vulnerability marker MMP-9. However, NRG1-III did not have a significant effect on male mice, indicating relevant sex differences. These findings indicate that increasing NRG1-III at the spinal cord is a promising approach for promoting MN protection and functional improvement in ALS.

Neuregulin 1/ErbB4 signaling attenuates neuronal cell damage under oxygen-glucose deprivation in primary hippocampal neurons

The hippocampus is one of the most important brain areas of cognition. This region is particularly sensitive to hypoxia and ischemia. Neuregulin-1 (NRG1) has been shown to be able to protect against focal cerebral ischemia. The aim of the present study was to investigate the neuroprotective effect of NRG1 in primary hippocampal neurons and its underlying mechanism. Our data showed oxygen-glucose deprivation (OGD)-induced cytotoxicity and overexpression of ErbB4 in primary hippocampal neurons. Moreover, pretreatment with NRG1 could inhibit OGD-induced overexpression of ErbB4. In addition, NRG1 significantly attenuated neuronal death induced by OGD. The neuroprotective effect of NRG1 was blocked in ischemic neurons after pretreatment with AG1478, an inhibitor of ErbB4, but not after pretreatment with AG879, an inhibitor of ErbB2. These results indicate an important role of ErbB4 in NRG1-mediated neuroprotection, suggesting that endogenous ErbB4 might serve as a valuable therapeutic target for treating global cerebral ischemia.

NRG1-ErbB4 signaling promotes functional recovery in a murine model of traumatic brain injury via regulation of GABA release

Traumatic brain injury (TBI) is a serious health problem in the world. However, little is known about the pathogenesis and molecular mechanisms of TBI. Here, we show that TBI activates neuregulin 1 (NRG1)-ErbB4 signaling, with an increased expression of NRG1 and ErbB4 in the traumatic region. Specifically knocking out ErbB4 in parvalbumin-positive (PV⁺) interneurons exacerbates motor function deficits in mice after TBI. Consistently, PV-ErbB4^-/- mice showed larger necrotic area and more edema when compared with PV-ErbB4^+/+ mice. Replenishment of NRG1 through intranasal application of the recombinant protein in PV-ErbB4^+/+ mice enhanced neurological function. Moreover, using an in vitro neuronal culture system, we found that NRG1-ErbB4 signaling protects neurons from glutamate-induced death, and such protective effects could be diminished by GABA receptor antagonist. These results indicate that NRG-ErbB4 signaling protects cortical neurons from TBI-induced damage, and such effect is probably mediated by promoting GABA activity. Taken together, these findings unveil a previously unappreciated role for NRG1-ErB4 signaling in preventing neuronal cell death during functional recovery after TBI.

Ginsenoside Rb1 Promotes Motor Functional Recovery and Axonal Regeneration in Post-stroke Mice through cAMP/PKA/CREB Signaling Pathway

The central nervous system (CNS) has a poor self-repairing capability after injury because of the inhibition of axonal regeneration by many myelin-associated inhibitory factors. Therefore, ischemic stroke usually leads to disability. Previous studies reported that Ginsenoside Rb1 (GRb1) plays a role in neuronal protection in acute phase after ischemic stroke, but its efficacy in post-stroke and the underlying mechanism are not clear. Recent evidences demonstrated GRb1 promotes neurotransmitter release through the cAMP-depend protein kinase A (PKA) pathway, which is related to axonal regeneration. The present study aimed to determine whether GRb1 improves long-term motor functional recovery and promotes cortical axon regeneration in post-stroke. Adult male C57BL/6 mice were subjected to distal middle cerebral artery occlusion (dMCAO). GRb1 solution (5 mg/ml) or equal volume of normal saline was injected intraperitoneally for the first time at 24 h after surgery, and then daily injected until day 14. Day 3, 7, 14 and 28 after dMCAO were used as observation time points. Motor functional recovery was assessed with Rota-rod test and grid walking task. The expression of growth-associated protein 43 (GAP43) and biotinylated dextran amine (BDA) was measured to evaluate axonal regeneration. The levels of cyclic AMP (cAMP) and PKA were measured by Elisa, PKAc and phosphorylated cAMP response element protein (pCREB) were determined by western blot. Our results shown that GRb1 treatment improved motor function and increased the expression of GAP43 and BDA in ipsilesional and contralateral cortex. GRb1 significantly elevated cAMP and PKA, increased the protein expression of PKAc and pCREB. However, the effects of GRb1 were eliminated by H89 intervention (a PKA inhibitor). These results suggested that GRb1 improved functional recovery in post-stroke by stimulating axonal regeneration and brain repair. The underlying mechanism might be up-regulating the expression of cAMP/PKA/CREB pathway.

Neuroprotection by Exogenous and Endogenous Neuregulin-1 in Mouse Models of Focal Ischemic Stroke

Identifying novel neuroprotectants that can halt or reverse the neurological effects of stroke is of interest to both clinicians and scientists. We and others previously showed the pre-clinical neuroprotective efficacy of neuregulin-1 (NRG-1) in rats following focal brain ischemia. In this study, we examined neuroprotection by exogenous and endogenous NRG-1 using a mouse model of ischemic stroke. C57BL6 mice were subjected to middle cerebral artery occlusion (MCAO) followed by reperfusion. NRG-1 or vehicle was infused intra-arterially (i.a.) or intravenously (i.v.) after MCAO and before the onset of reperfusion. NRG-1 treatment (16 μg/kg; i.a.) reduced cerebral cortical infarct volume by 72% in mice when delivered post-ischemia. NRG-1 also inhibited neuronal injury as measured by Fluoro Jade B labeling and rescued NeuN immunoreactivity in neurons. Neuroprotection by NRG-1 was also observed in mice when administered i.v. (100 μg/kg) in both male and female mice. We investigated whether endogenous NRG-1 was neuroprotective using male and female heterozygous NRG-1 knockout mice (NRG-1+/-) compared with wild-type mice (WT) littermates. NRG-1+/- and WT mice were subjected to MCAO for 45 min, and infarct size was measured 24 h following MCAO. NRG-1+/- mice displayed a sixfold increase in cortical infarct size compared with WT mice. These results demonstrate that NRG-1 treatment mitigates neuronal damage following cerebral ischemia. We further showed that reduced endogenous NRG-1 results in exacerbated neuronal injury in vivo. These findings suggest that NRG-1 represents a promising therapy to treat stroke in human patients.

Neuregulin-1/ErbB network: An emerging modulator of nervous system injury and repair

Neuregulin-1 (Nrg-1) is a member of the Neuregulin family of growth factors with essential roles in the developing and adult nervous system. Six different types of Nrg-1 (Nrg-1 type I-VI) and over 30 isoforms have been discovered; however, their specific roles are not fully determined. Nrg-1 signals through a complex network of protein-tyrosine kinase receptors, ErbB2, ErbB3, ErbB4 and multiple intracellular pathways. Genetic and pharmacological studies of Nrg-1 and ErbB receptors have identified a critical role for Nrg-1/ErbB network in neurodevelopment including neuronal migration, neural differentiation, myelination as well as formation of synapses and neuromuscular junctions. Nrg-1 signaling is best known for its characterized role in development and repair of the peripheral nervous system (PNS) due to its essential role in Schwann cell development, survival and myelination. However, our knowledge of the impact of Nrg-1/ErbB on the central nervous system (CNS) has emerged in recent years. Ongoing efforts have uncovered a multi-faceted role for Nrg-1 in regulating CNS injury and repair processes. In this review, we provide a timely overview of the most recent updates on Nrg-1 signaling and its role in nervous system injury and diseases. We will specifically highlight the emerging role of Nrg-1 in modulating the glial and immune responses and its capacity to foster neuroprotection and remyelination in CNS injury. Nrg-1/ErbB network is a key regulatory pathway in the developing nervous system; therefore, unraveling its role in neuropathology and repair can aid in development of new therapeutic approaches for nervous system injuries and associated disorders.

Neuregulin-1 Fosters Supportive Interactions between Microglia and Neural Stem/Progenitor Cells

Microglia play diverse roles in homeostasis and pathology of the central nervous system (CNS). Their response to injury or insult is critical for initiating neuroinflammation and tissue damage as well as resolution of inflammation and wound healing. Changes to the microenvironment of microglia appear to be a key determinant of their phenotype and their role in the endogenous repair process in the injured or diseased CNS. Our recent findings have identified a positive role for neuregulin-1 (Nrg-1) in regulating immune response in spinal cord injury and focal demyelinating lesions. We show that increasing the tissue availability of Nrg-1 after injury can promote endogenous repair by modulating neuroinflammation. In the present study, we sought to elucidate the specific role of Nrg-1 in regulating microglial activity and more importantly their influence on the behavior of neural stem/progenitor cells (NPCs). Using injury-relevant in vitro systems, we demonstrate that Nrg-1 attenuates the expression of proinflammatory mediators in activated microglia. Moreover, we provide novel evidence that availability of Nrg-1 can restore the otherwise suppressed phagocytic ability of proinflammatory microglia. Interestingly, the presence of Nrg-1 in the microenvironment of proinflammatory microglia mitigates their inhibitory effects on NPC proliferation. Nrg-1 treated proinflammatory microglia also augment mobilization of NPCs, while they had no influence on their suppressive effects on NPC differentiation. Mechanistically, we show that Nrg-1 enhances the interactions of proinflammatory microglia and NPCs, at least in part, through reduction of TNF-α expression in microglia. These findings provide new insights into the endogenous regulation of microglia-NPC interactions and identify new potential targets for optimizing this important crosstalk during the regenerative process after CNS injury and neuroinflammatory conditions.

White-matter repair: Interaction between oligodendrocytes and the neurovascular unit

There are currently no adequate treatments for white-matter injury, which often follows central nervous system maladies and their accompanying neurodegenerative processes. Indeed, the white matter is compromised by the deterioration of the blood–brain barrier and the demyelination of neuronal axons. Key repairs to the white matter are mediated by oligodendrocyte lineage cells after damaging events. Oligodendrocytes are supported by other cells in the neurovascular unit and these cells collaborate in processes such as angiogenesis, neurogenesis, and oligodendrogenesis. Understanding the various interactions between these cells and oligodendrocytes will be imperative for developing reparative therapies for impaired white matter. This minireview will discuss how oligodendrocytes and oligodendrocyte lineage cells mend damage to the white matter and restore brain function ensuing neural injury.

Role of oligodendrocyte-neurovascular unit in white matter repair

White matter injury caused by acute or chronic neuropathologies is a major characteristic of many CNS diseases, and an effective treatment is still out of our reach. White matter damage is associated with the collapse of the axon-myelin complex and with blood-brain barrier (BBB) breakdown, which results in disruption of white matter function. While white matter damage cannot completely resolve spontaneously, some compensative responses may occur after the injury. Oligodendrocyte lineage cells perform critical functions in repairing damaged white matter. In this mini-review, we will focus on the reparative actions of the oligodendrocytes, and highlight the important role of oligodendrocyte lineage cells in brain recovery after injury.

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.

Evaluation of neuregulin-1's neuroprotection against ischemic injury in rats using diffusion tensor imaging

Stroke is a devastating neurovascular disorder that results in damage to neurons and white matter tracts. It has been previously demonstrated that neuregulin-1 (NRG-1) protects neurons from ischemic injury following stroke. Here, diffusion tensor imaging (DTI) was utilized to characterize the effects of NRG-1 treatment on cererbral infarction and integrity of white matter after ischemic insult using a permanent middle celebral artery occlusion (pMCAo) rat model. In the present study, sixteen Sprague-Dawley rats underwent pMCAo surgery and received either a single intra-arterial bolus (20 μg/kg) dose of NRG-1 or saline immediately prior to pMCAo. MRI including T2-weighted imaging and DTI was performed in the first 3 h post stroke, and repeated 48 h later. It is found that the stroke infarction was significantly reduced in the NRG-1 treated group. Also, NRG-1 prevented the reduction of fractional anisotropy (FA) in white matter tracts of fornix and corpus callosum (CC), indicating its protection of CC and fornix white matter bundles from ischemia insult. As a conclusion, the present DTI results demonstrate that NRG-1 has significantly neuroprotective effects in both cerebral cortex and white matter including corpus callosum and fornix during acute stroke. In particular, NRG-1 is more effective on stroke lesion with mild ischemia. As CC and fornix white matter bundles play critical roles in transcallosal connectivity and hippocampal projections respectively in the central nervous system, the findings could provide complementary information for better understanding the biological mechanism of NRG-1's neuroprotection in ischemic tissues and neurobehavioral effects.

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.

Design and optimization of PLGA microparticles for controlled and local delivery of Neuregulin-1 in traumatic spinal cord injury

Spinal cord injury (SCI) results in significant tissue damage that underlies functional impairments. Pharmacological interventions to confer neuroprotection and promote cell replacement are essential for SCI repair. We previously reported that Neuregulin-1 (Nrg-1) is acutely and permanently downregulated after SCI. Nrg-1 is a critical growth factor for differentiation of neural precursor cells (NPCs) into myelinating oligodendrocytes. We showed that intrathecal delivery of Nrg-1 enhances oligodendrocyte replacement following SCI. While an effective delivery system, intrathecal and systemic administration of growth factors with diverse biological targets may pose adverse off-target effects. Here, we have developed and optimized an injectable biodegradable poly(lactic-co-glycolic acid) (PLGA) microparticles system for sustained and prolonged intraspinal delivery of Nrg-1 in SCI. Recombinant human Nrg-1β1 peptide was encapsulated into PLGA microparticles. Optimal Nrg-1 release rate and duration were achieved by manipulating the porosity and size of PLGA particles. Our in vitro analysis showed a direct correlation between particle size and porosity with Nrg-1 release rate, while Nrg-1 loading efficiency in PLGA microparticles was inversely correlated with particle porosity. In SCI, local intraspinal injection of PLGA-Nrg-1 microparticles maintained significantly higher tissue levels of Nrg-1 for a long-term duration compared to Nrg-1 delivered intrathecally by osmotic pumps. Bioactivity of Nrg-1 in PLGA microparticles was verified by promoting oligodendrocyte differentiation of NPCs in vitro, and preservation of oligodendrocytes and axons in SCI. PLGA-Nrg-1 also attenuated neuroinflammation and glial scarring following SCI. We show, for the first time, the feasibility, efficacy and safety of PLGA microparticle system for local and controlled administration of Nrg-1 in SCI.

Longitudinal MRI evaluation of neuroprotective effects of pharmacologically induced hypothermia in experimental ischemic stroke

Pharmacologically induced hypothermia (PIH) shows promising neuroprotective effects after stroke insult. However, the dynamic evolution of stroke infarct during the hypothermic therapy has not been understood very well. In the present study, MRI was utilized to longitudinally characterize the infarct evolution in a mouse model of ischemic stroke treated by PIH using the neurotensin agonist HPI201. Adult male C57BL/6 mice underwent permanent occlusion of the right middle cerebra artery (MCA). Each animal received a vehicle or HPI201 intraperitoneal injection. The temporal changes of stroke lesion were examined using T2-weighted imaging and diffusion-weighted imaging (DWI) in the acute phase (1-3h) and 24h post stroke. Significantly reduced infarct and edema volumes were observed in PIH treated stroke mice, in agreement with TTC staining findings. Also, the TUNEL staining results indicated apoptotic cells were widely distributed among the ischemic cortex in control group but limited in PIH treated mice. Dramatically reduced growth rate of infarction was seen in PIH treated stroke mice. These results demonstrate HPI201 has strong neuroprotection effects during acute stroke. In particular, MRI with the numerical modelling of temporal infarct evolution could provide a unique means to examine and predict the dynamic response of the PIH treatment on infarct evolution.

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.

Neuroprotective effects of dexmedetomidine against hyperoxia-induced injury in the developing rat brain

Dexmedetomidine (DEX) is a highly selective agonist of α2-receptors with sedative, anxiolytic, and analgesic properties. Neuroprotective effects of dexmedetomidine have been reported in various brain injury models. In the present study, we investigated the effects of dexmedetomidine on hippocampal neurogenesis, specifically the proliferation capacity and maturation of neurons and neuronal plasticity following the induction of hyperoxia in neonatal rats. Six-day old sex-matched Wistar rats were exposed to 80% oxygen or room air for 24 h and treated with 1, 5 or 10 μg/kg of dexmedetomidine or normal saline. A single pretreatment with DEX attenuated the hyperoxia-induced injury in terms of neurogenesis and plasticity. In detail, both the proliferation capacity (PCNA+ cells) as well as the expression of neuronal markers (Nestin+, PSA-NCAM+, NeuN+ cells) and transcription factors (SOX2, Tbr1/2, Prox1) were significantly reduced under hyperoxia compared to control. Furthermore, regulators of neuronal plasticity (Nrp1, Nrg1, Syp, and Sema3a/f) were also drastically decreased. A single administration of dexmedetomidine prior to oxygen exposure resulted in a significant up-regulation of expression-profiles compared to hyperoxia. Our results suggest that dexmedetomidine may have neuroprotective effects in an acute hyperoxic model of the neonatal rat.

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.

Blocking the phosphatidylinositol 3-kinase pathway inhibits neuregulin-1-mediated rescue of neurotoxicity induced by Aβ1-42

OBJECTIVES

Neuregulin-1 (NRG1) has an important role in both the development and the plasticity of the brain as well as neuroprotective properties. In this study, we investigated the downstream pathways of NRG1 signalling and their role in the prevention of Aβ1-42 -induced neurotoxicity.

METHODS

Lactate dehydrogenase (LDH) release, reactive oxygen species (ROS) generation, superoxide dismutase (SOD) activity and TUNEL staining were assayed to examine the neuroprotective properties in primary rat cortical neurons.

KEY FINDINGS

The inhibition of PI3K/Akt activation abolished the ability of NRG1 to prevent Aβ1-42 -induced LDH release and increased TUNEL-positive cell count and reactive oxygen species accumulation in primary cortical neurons.

CONCLUSIONS

Our results demonstrate that NRG1 signalling exerts a neuroprotective effect against Aβ1-42 -induced neurotoxicity via activation of the PI3K/Akt pathway. Furthermore, this suggests that NRG1 has neuroprotective potential for the treatment of AD.

Microenvironmental regulation of oligodendrocyte replacement and remyelination in spinal cord injury

Myelin is a proteolipid sheath enwrapping axons in the nervous system that facilitates signal transduction along the axons. In the central nervous system (CNS), oligodendrocytes are specialized glial cells responsible for myelin formation and maintenance. Following spinal cord injury (SCI), oligodendroglia cell death and myelin damage (demyelination) cause chronic axonal damage and irreparable loss of sensory and motor functions. Accumulating evidence shows that replacement of damaged oligodendrocytes and renewal of myelin (remyelination) are promising approaches to prevent axonal degeneration and restore function following SCI. Neural precursor cells (NPCs) and oligodendrocyte progenitor cells (OPCs) are two main resident cell populations in the spinal cord with innate capacities to foster endogenous oligodendrocyte replacement and remyelination. However, due to the hostile microenvironment of SCI, the regenerative capacity of these endogenous precursor cells is conspicuously restricted. Activated resident glia, along with infiltrating immune cells, are among the key modulators of secondary injury mechanisms that create a milieu impermissible to oligodendrocyte differentiation and remyelination. Recent studies have uncovered inhibitory roles for astrocyte-associated molecules such as matrix chondroitin sulfate proteoglycans (CSPGs), and a plethora of pro-inflammatory cytokines and neurotoxic factors produced by activated microglia/macrophages. The quality of axonal remyelination is additionally challenged by dysregulation of the supportive growth factors required for maturation of new oligodendrocytes and axo-oligodendrocyte signalling. Careful understanding of factors that modulate the activity of endogenous precursor cells in the injury microenvironment is a key step in developing efficient repair strategies for remyelination and functional recovery following SCI.

An optimized dosing regimen of cimaglermin (neuregulin 1β3, glial growth factor 2) enhances molecular markers of neuroplasticity and functional recovery after permanent ischemic stroke in rats

Cimaglermin (neuregulin 1β3, glial growth factor 2) is a neuregulin growth factor family member in clinical development for chronic heart failure. Previously, in a permanent middle cerebral artery occlusion (pMCAO) rat stroke model, systemic cimaglermin treatment initiated up to 7 days after ischemia onset promoted recovery without reduced lesion volume. Presented here to extend the evidence are two studies that use a rat stroke model to evaluate the effects of cimaglermin dose level and dose frequency initiated 24 hr after pMCAO. Forelimb‐ and hindlimb‐placing scores (proprioceptive behavioral tests), body‐swing symmetry, and infarct volume were compared between treatment groups (n = 12/group). Possible mechanisms underlying cimaglermin‐mediated neurologic recovery were examined through axonal growth and synapse formation histological markers. Cimaglermin was evaluated over a wider dose range (0.02, 0.1, or 1.0 mg/kg) than doses previously shown to be effective but used the same dosing regimen (2 weeks of daily intravenous administration, then 1 week without treatment). The dose‐frequency study used the dose‐ranging study's most effective dose (1.0 mg/kg) to compare daily, once per week, and twice per week dosing for 3 weeks (then 1 week without treatment). Dose‐ and frequency‐dependent functional improvements were observed with cimaglermin without reduced lesion volume. Cimaglermin treatment significantly increased growth‐associated protein 43 expression in both hemispheres (particularly somatosensory and motor cortices) and also increased synaptophysin expression. These data indicate that cimaglermin enhances recovery after stroke. Immunohistochemical changes were consistent with axonal sprouting and synapse formation but not acute neuroprotection. Cimaglermin represents a potential clinical development candidate for ischemic stroke treatment. © 2015 The Authors. Journal of Neuroscience Research Published by Wiley Periodicals, Inc.

Mechanisms of cell-cell interaction in oligodendrogenesis and remyelination after stroke

White matter damage is a clinically important aspect of several central nervous system diseases, including stroke. Cerebral white matter primarily consists of axonal bundles ensheathed with myelin secreted by mature oligodendrocytes, which play an important role in neurotransmission between different areas of gray matter. During the acute phase of stroke, damage to oligodendrocytes leads to white matter dysfunction through the loss of myelin. On the contrary, during the chronic phase, white matter components promote an environment, which is favorable for neural repair, vascular remodeling, and remyelination. For effective remyelination to take place, oligodendrocyte precursor cells (OPCs) play critical roles by proliferating and differentiating into mature oligodendrocytes, which help to decrease the burden of axonal injury. Notably, other types of cells contribute to these OPC responses under the ischemic conditions. This mini-review summarizes the non-cell autonomous mechanisms in oligodendrogenesis and remyelination after white matter damage, focusing on how OPCs receive support from their neighboring cells. This article is part of a Special Issue entitled SI: Cell Interactions In Stroke.

Spatio-temporal assessment of the neuroprotective effects of neuregulin-1 on ischemic stroke lesions using MRI

The neuroprotective effects of neuregulin-1 (NRG-1) on stroke lesions were assessed longitudinally in rats with middle cerebral artery occlusion (MCAo) using MRI. Sprague-Dawley rats (n=16, 250±20g) underwent permanent MCAo surgery with cerebral blood flow (CBF) monitored by laser doppler flowmetry at ipsilateral side of bregma for 20min post-occlusion. A single 50μl bolus dose of NRG-1 or vehicle was administered into the left internal carotid artery immediately prior to MCAo. The expansion of the ischemic lesion into the cortex was attenuated by NRG-1 over a 48-hour (h) time span as measured by diffusion weighted imaging (DWI). The final infarct volumes of NRG-1 treated rats were significantly smaller than those of the vehicle treated rats at 48h (264.8±192.1 vs. 533.4±175.5mm(3), p<0.05). The NRG-1 treated rats were further subdivided into 2 subgroups according to their CBF reduction during stroke surgery: mild ischemia (<70% CBF reduction) or severe ischemia (>70% CBF reduction). In particular, ischemic infarction was not usually observed in the cortex of NRG-1 treated rats with mild ischemia at 3 and 48h post-occlusion. Histological results validated the imaging findings and demonstrated that NRG-1 treated rats had fewer injured neurons in peri-infarct areas 48h post-ischemia. In summary, the neuroprotective effect of NRG-1 in the pMCAo stroke model was demonstrated by prevention of ischemic lesion expansion, reduced infarct volume and protection of neurons from ischemic damage.

Neuregulin-1 inhibits neuroinflammatory responses in a rat model of organophosphate-nerve agent-induced delayed neuronal injury

Background

Neuregulin-1 (NRG-1) has been shown to act as a neuroprotectant in animal models of nerve agent intoxication and other acute brain injuries. We recently demonstrated that NRG-1 blocked delayed neuronal death in rats intoxicated with the organophosphate (OP) neurotoxin diisopropylflurophosphate (DFP). It has been proposed that inflammatory mediators are involved in the pathogenesis of OP neurotoxin-mediated brain damage.

Methods

We examined the influence of NRG-1 on inflammatory responses in the rat brain following DFP intoxication. Microglial activation was determined by immunohistchemistry using anti-CD11b and anti-ED1 antibodies. Gene expression profiling was performed with brain tissues using Affymetrix gene arrays and analyzed using the Ingenuity Pathway Analysis software. Cytokine mRNA levels following DFP and NRG-1 treatment was validated by real-time reverse transcription polymerase chain reaction (RT-PCR).

Results

DFP administration resulted in microglial activation in multiple brain regions, and this response was suppressed by treatment with NRG-1. Using microarray gene expression profiling, we observed that DFP increased mRNA levels of approximately 1,300 genes in the hippocampus 24 h after administration. NRG-1 treatment suppressed by 50% or more a small fraction of DFP-induced genes, which were primarily associated with inflammatory responses. Real-time RT-PCR confirmed that the mRNAs for pro-inflammatory cytokines interleukin-1β (IL-1β) and interleukin-6 (IL-6) were significantly increased following DFP exposure and that NRG-1 significantly attenuated this transcriptional response. In contrast, tumor necrosis factor α (TNFα) transcript levels were unchanged in both DFP and DFP + NRG-1 treated brains relative to controls.

Conclusion

Neuroprotection by NRG-1 against OP neurotoxicity is associated with the suppression of pro-inflammatory responses in brain microglia. These findings provide new insight regarding the molecular mechanisms involved in the neuroprotective role of NRG-1 in acute brain injuries.

Evidence for the use of isoflurane as a replacement for chloral hydrate anesthesia in experimental stroke: an ethical issue

Since an ethical issue has been raised regarding the use of the well-known anesthetic agent chloral hydrate, owing to its mutagenic and carcinogenic effects in animals, attention of neuroscientists has turned to finding out an alternative agent able to meet not only potency, safety, and analgesic efficacy, but also reduced neuroprotective effect for stroke research. The aim of this study was to compare the potential of chloral hydrate and isoflurane for both modulating the action of the experimental neuroprotectant MK801 and exerting analgesia. After middle cerebral artery occlusion in rats, no difference was observed in 24 h survival rate, success of ischemia, or infarct volume reduction between both anesthetics. However, isoflurane exerted a more pronounced analgesic effect than chloral hydrate as evidenced by formalin test 3 hours after anesthesia onset, thus encouraging the use of isoflurane in experimental stroke models.

Neuregulin-1 attenuates mortality associated with experimental cerebral malaria

Background

Cerebral Malaria (CM) is a diffuse encephalopathy caused by Plasmodium falciparum infection. Despite availability of antimalarial drugs, CM-associated mortality remains high at approximately 30% and a subset of survivors develop neurological and cognitive disabilities. While antimalarials are effective at clearing Plasmodium parasites they do little to protect against CM pathophysiology and parasite-induced brain inflammation that leads to seizures, coma and long-term neurological sequelae in CM patients. Thus, there is urgent need to explore therapeutics that can reduce or prevent CM pathogenesis and associated brain inflammation to improve survival. Neuregulin-1 (NRG-1) is a neurotrophic growth factor shown to protect against brain injury associated with acute ischemic stroke (AIS) and neurotoxin exposure. However, this drug has not been tested against CM-associated brain injury. Since CM-associated brain injuries and AIS share similar pathophysiological features, we hypothesized that NRG-1 will reduce or prevent neuroinflammation and brain damage as well as improve survival in mice with late-stage experimental cerebral malaria (ECM).

Methods

We tested the effects of NRG-1 on ECM-associated brain inflammation and mortality in P. berghei ANKA (PbA)-infected mice and compared to artemether (ARM) treatment; an antimalarial currently used in various combination therapies against malaria.

Results

Treatment with ARM (25 mg/kg/day) effectively cleared parasites and reduced mortality in PbA-infected mice by 82%. Remarkably, NRG-1 therapy (1.25 ng/kg/day) significantly improved survival against ECM by 73% despite increase in parasite burden within NRG-1-treated mice. Additionally, NRG-1 therapy reduced systemic and brain pro-inflammatory factors TNFalpha, IL-6, IL-1alpha and CXCL10 and enhanced anti-inflammatory factors, IL-5 and IL-13 while decreasing leukocyte accumulation in brain microvessels.

Conclusions

This study suggests that NRG-1 attenuates ECM-associated brain inflammation and injuries and may represent a novel supportive therapy for the management of CM.

Effects of neuregulin-1β on growth-associated protein 43 expression in dorsal root ganglion neurons with excitotoxicity induced by glutamate in vitro

Neuregulin-1β (NRG-1β) is a growth factor with potent neuroprotective capacity. Growth-associated protein 43 (GAP-43) is expressed in dorsal root ganglion (DRG) neurons and an indicator of neuronal survival in vitro. The purpose of present study is to evaluate the effects of NRG-1β on GAP-43 expression in DRG neurons with excitotoxicity induced by glutamate (Glu) in vitro. The phosphatidylinositol 3-kinase (PI3K)/Akt and extracellular signal-regulated protein kinase 1/2 (ERK1/2) signaling pathways involved in these effects were also determined. Embryonic rat DRG neurons were treated with Glu in the absence or presence of NRG-1β and PI3K inhibitor LY294002 and/or ERK1/2 inhibitor PD98059. After that, GAP-43 mRNA and GAP-43 protein levels were analyzed by real time-PCR and western blot assay, respectively. GAP-43 expression in situ was determined by immunofluorescent labeling. The results showed that the decreased GAP-43 levels induced by Glu could be partially reversed by the presence of NRG-1β. Inhibitors (LY294002, PD98059) either alone or in combination blocked the effects of NRG-1β. These data provide new insights of the actions of NRG-1β in sensory neurons.

Neuregulin in cardiovascular development and disease

Studies in genetically modified mice have demonstrated that neuregulin-1 (NRG-1), along with the erythroblastic leukemia viral oncogene homolog (ErbB) 2, 3, and 4 receptor tyrosine kinases, is necessary for multiple aspects of cardiovascular development. These observations stimulated in vitro and in vivo animal studies, implicating NRG-1/ErbB signaling in the regulation of cardiac cell biology throughout life. Cardiovascular effects of ErbB2-targeted cancer therapies provide evidence in humans that ErbB signaling plays a role in the maintenance of cardiac function. These and other studies suggest a conceptual model in which a key function of NRG-1/ErbB signaling is to mediate adaptations of the heart to physiological and pathological stimuli through activation of intracellular kinase cascades that regulate tissue plasticity. Recent work implicates NRG-1/ErbB signaling in the regulation of multiple aspects of cardiovascular biology, including angiogenesis, blood pressure, and skeletal muscle responses to exercise. The therapeutic potential of recombinant NRG-1 as a potential treatment for heart failure has been demonstrated in animal models and is now being explored in clinical studies. NRG-1 is found in human serum and plasma, and it correlates with some clinical parameters, suggesting that it may have value as an indicator of prognosis. In this review, we bring together this growing literature on NRG-1 and its significance in cardiovascular development and disease.

Computational identification of conserved transcription factor binding sites upstream of genes induced in rat brain by transient focal ischemic stroke

Microarray analysis has been used to understand how gene regulation plays a critical role in neuronal injury, survival and repair following ischemic stroke. To identify the transcriptional regulatory elements responsible for ischemia-induced gene expression, we examined gene expression profiles of rat brains following focal ischemia and performed computational analysis of consensus transcription factor binding sites (TFBS) in the genes of the dataset. In this study, rats were sacrificed 24 h after middle cerebral artery occlusion (MCAO) stroke and gene transcription in brain tissues following ischemia/reperfusion was examined using Affymetrix GeneChip technology. The CONserved transcription FACtor binding site (CONFAC) software package was used to identify over-represented TFBS in the upstream promoter regions of ischemia-induced genes compared to control datasets. CONFAC identified 12 TFBS that were statistically over-represented from our dataset of ischemia-induced genes, including three members of the Ets-1 family of transcription factors (TFs). Microarray results showed that mRNA for Ets-1 was increased following tMCAO but not pMCAO. Immunohistochemical analysis of Ets-1 protein in rat brains following MCAO showed that Ets-1 was highly expressed in neurons in the brain of sham control animals. Ets-1 protein expression was virtually abolished in injured neurons of the ischemic brain but was unchanged in peri-infarct brain areas. These data indicate that TFs, including Ets-1, may influence neuronal injury following ischemia. These findings could provide important insights into the mechanisms that lead to brain injury and could provide avenues for the development of novel therapies.

Neuregulin-1 exerts protective effects against neurotoxicities induced by C-terminal fragments of APP via ErbB4 receptor

Neuregulin-1 (NRG1) plays important roles in the development and plasticity of the brain, and it is also reported to have potent neuroprotective properties. We previously reported that NRG1 has neuroprotective actions against Swedish amyloid precursor protein-induced neurotoxicity. In addition to the amyloid beta peptide, other metabolites of amyloid precursor protein (APP) such as the C-terminal fragments of APP (APP-CTs) have been reported to possess cytotoxic effects in neuronal cells. In this study, we investigated whether NRG1 exerts neuroprotective effects against APP-CTs and attempted to determine its neuroprotective mechanisms. NRG1 attenuated the neurotoxicities induced by the expression of APP-CTs in neuronal cells. NRG1 also reduced the accumulation of reactive oxygen species and attenuated mitochondrial membrane potential loss induced by APP-CTs. In addition, NRG1 upregulated the expression of the anti-apoptotic protein Bcl-2. This effect was blocked by the inhibition of ErbB4, a key NRG1 receptor. Taken together, these results demonstrate the neuroprotective potential of NRG1 in Alzheimer's disease.

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.

Neuregulin1β1 protects oligodendrocyte progenitor cells from oxygen glucose deprivation injury induced apoptosis via ErbB4-dependent activation of PI3-kinase/Akt

Mounting evidence suggests that the injury of oligodendrocyte progenitor cells (OPCs) caused by hypoxia plays a pivotal role in periventricular white matter injury (PWMI) causation. We investigated the potential role of active extracellular domain of Neuregulin1 isotypeβ1 (NRG1β1)/ErbB signaling in protecting OPCs from oxygen glucose deprivation (OGD) induced apoptosis. At different time points, endogenous NRG1β1 protein was analyzed after OGD. Escalating dosages of NRG1β1 were used to treat OPCs with OGD, and the apoptosis was measured, as well as the expression of ErbB receptors, Akt and Erk phosphorylation and caspase3 activation. OGD damage resulted in decreased expression of endogenous NRG1β1. In parallel, NRG1β1 treatment promoted the expression of p-ErbB4 receptor, phosphorylated Akt and inhibited caspase3 activation. Furthermore, the activation of PI3-kinase/Akt by NRG1β1 was ErbB4 dependent. Our data demonstrated that NRG1β1 protected OPCs from OGD induced apoptosis and the possible protective mechanism is linking with ErbB4-dependent activation of PI3-kinase/Akt pathway.

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.

Antioxidant Activities of Dracocephalum tanguticum Maxim Extract and Its Up-Regulation on the Expression of Neurotrophic Factors in a Rat Model of Permanent Focal Cerebral Ischemia

The aim of this study was to investigate the effect of a BuOH-soluble fraction from Dracocephalum tanguticum Maxim (DME), which contained 52% of total flavonoid, on the cerebral ischemia injury induced by permanent middle cerebral artery occlusion (pMCAO) in rats. RT-PCR and Western blot analysis showed that DME (30 mg/kg/day for seven days) by intragastric administration modulated the mRNA expression and protein synthesis of two neurotrophic factors: brain-derived neurotrophic factor (BDNF) and neurotrophin 3 (NT-3). DME was effective in stimulating BDNF mRNA expression and protein synthesis in the ipsilateral frontal cortex (IFC) of both the sham-operated and pMCAO rats and this effect was also observed in the hippocampus of the pMCAO rats. DME significantly increased NT-3 mRNA expression and protein synthesis in the IFC and hippocampus of the pMCAO rats, although it had no effect on NT-3 expression in the sham-operated groups. Meanwhile, DME also decreased the malondialdehyde contents in the hippocampus of the sham-operated and pMCAO groups, and significantly attenuated the decrease of endogenous antioxidant (superoxide dismutase, glutathione peroxidase and catalase) activities in both the IFC and hippocampus of the rats after ischemia insult injury. Moreover, DME facilitated the neurobehavioral recovery after the cerebral ischemia. These findings suggested that DME has potential for treatment of ischemia-induced brain damage through stimulation of antioxidant activity and neurotrophic factor synthesis.

Neuregulin-1 protects against neurotoxicities induced by Swedish amyloid precursor protein via the ErbB4 receptor

Neuregulin-1 (NRG1) plays an important role in the development and plasticity of the brain and exhibits potent neuroprotective properties. However, little information on its role in Alzheimer's disease (AD) is known. The neuroprotective effect and mechanisms of NRG1 in SH-SY5Y cells overexpressing the Swedish mutant form of amyloid precursor protein (Swe-APP) and primary cortical neuronal cells treated with amyloid beta peptide(1-42) (Aβ(1-42)) were investigated in this study. NRG1 attenuated Swe-APP- or Aβ(1-42)-induced lactate dehydrogenase (LDH) release in a concentration-dependent manner. The mitigating effects of NRG1 on neuronal cell death were blocked by ErbB4 inhibition, a key NRG1 receptor, which suggests a role of ErbB4 in the neuroprotective function of NRG1. Moreover, NRG1 reduced the number of Swe-APP- and Aβ(1-42)-induced TUNEL-positive SH-SY5Y cells and primary cortical neurons, respectively. NRG1 reduced the accumulation of reactive oxygen species and attenuated Swe-APP-induced mitochondrial membrane potential loss. NRG1 also induced the upregulation of the expression of the anti-apoptotic protein, Bcl-2, and decreased caspase-3 activation. Collectively, our results demonstrate that NRG1 exerts neuroprotective effects via the ErbB4 receptor, which suggests the neuroprotective potential of NRG1 in AD.