Closed head injury induces up-regulation of ErbB-4 receptor at the site of injury

A comprehensive review of stroke-related signaling pathways and treatment in western medicine and traditional Chinese medicine

This review provides insight into the complex network of signaling pathways and mechanisms involved in stroke pathophysiology. It summarizes the historical progress of stroke-related signaling pathways, identifying potential interactions between them and emphasizing that stroke is a complex network disease. Of particular interest are the Hippo signaling pathway and ferroptosis signaling pathway, which remain understudied areas of research, and are therefore a focus of the review. The involvement of multiple signaling pathways, including Sonic Hedgehog (SHH), nuclear factor erythroid 2-related factor 2 (Nrf2)/antioxidant response element (ARE), hypoxia-inducible factor-1α (HIF-1α), PI3K/AKT, JAK/STAT, and AMPK in pathophysiological mechanisms such as oxidative stress and apoptosis, highlights the complexity of stroke. The review also delves into the details of traditional Chinese medicine (TCM) therapies such as Rehmanniae and Astragalus, providing an analysis of the recent status of western medicine in the treatment of stroke and the advantages and disadvantages of TCM and western medicine in stroke treatment. The review proposes that since stroke is a network disease, TCM has the potential and advantages of a multi-target and multi-pathway mechanism of action in the treatment of stroke. Therefore, it is suggested that future research should explore more treasures of TCM and develop new therapies from the perspective of stroke as a network disease.

ErbB Signaling Pathway Genes Are Differentially Expressed in Monozygotic Twins Discordant for Sports-Related Concussion

Transcriptional changes involved in neuronal recovery after sports-related concussion (SRC) may be obscured by inter-individual variation in mRNA expression and nonspecific changes related to physical exertion. Using a co-twin study, the objective of this study was to identify important differences in mRNA expression among a single pair of monozygotic (MZ) twins discordant for concussion. A pair of MZ twins were enrolled as part of a larger study of concussion biomarkers among collegiate athletes. During the study, Twin A sustained SRC, allowing comparison of mRNA expression to the nonconcussed Twin B. Twin A clinically recovered by Day 7. mRNA expression was measured pre-injury and at 6 h and 7 days postinjury using Affymetrix HG-U133 Plus 2.0 microarray. Changes in mRNA expression from pre-injury to each postinjury time point were compared between the twins; differences >1.5-fold were considered important. Kyoto Encyclopedia of Genes and Genomes identified biologic networks associated with important transcripts. Among 38,000 analyzed genes, important changes were identified in 153 genes. The ErbB (epidermal growth factor receptor) signaling pathway was identified as the top transcriptional network from pre-injury to 7 days postinjury. Genes in this pathway with important transcriptional changes included epidermal growth factor (2.41), epiregulin (1.73), neuregulin 1 (1.54) and mechanistic target of rapamycin (1.51). In conclusion, the ErbB signaling pathway was identified as a potential regulator of clinical recovery in a MZ twin pair discordant for SRC. A co-twin study design may be a useful method for identifying important gene pathways associated with concussion recovery.

Regulation of NRG-1-ErbB4 signaling and neuroprotection by exogenous neuregulin-1 in a mouse model of epilepsy

Temporal lobe epilepsy (TLE) is the most common form of focal epilepsy. Dysregulation of glutamate transporters has been a common finding across animal models of epilepsy and in patients with TLE. In this study, we investigate NRG-1/ErbB4 signaling in epileptogenesis and the neuroprotective effects of NRG-1 treatment in a mouse model of temporal lobe epilepsy. Using immunohistochemistry, we report the first evidence for NRG-1/ErbB4-dependent selective upregulation of glutamate transporter EAAC1 and bihemispheric neuroprotection by exogeneous NRG-1 in the intrahippocampal kainic acid (IHKA) model of TLE. Our findings provide evidence that dysregulation of glutamate transporter EAAC1 contributes to the development of epilepsy and can be therapeutically targeted to reduce neuronal death following IHKA-induced status epilepticus (SE).

Elevated neuregulin-1β levels correlate with plasma biomarkers of cerebral injury and high stroke risk in children with sickle cell anemia

Stroke, or cerebral infarction, is one of the most serious complications of sickle cell anemia (SCA) in childhood, potentially leading to impaired development and life-long physical and cognitive disabilities. About one in ten children with SCA are at risk for developing overt stroke and an additional 25% may develop silent cerebral infarcts. This is largely due to underlying cerebral injury caused by chronic cerebral ischemia and vascular insult associated with SCA. We previously identified two elevated markers of cerebral injury, plasma brain-derived neurotropic factor (BDNF) and platelet-derived growth factor (PDGF)-AA, in children with SCA and high stroke risk. The objective of this study was to investigate whether neuregulin-1β (NRG-1), an endogenous neuroprotective polypeptide may also be elevated in children with SCA. Neuregulin-1β is involved in the preservation of blood brain barrier integrity and brain microvascular cell viability and is cytoprotective in conditions of heme-induced injury and ischemia. Since elevated plasma heme and ischemia are signature characteristics of SCA, we hypothesized that NRG-1 would be elevated in children with SCA, and that NRG-1 levels would also correlate with our biomarkers of cerebral injury. Plasma NRG-1, BDNF and PDGF-AA levels were measured in children with SCA and healthy Controls. Plasma NRG-1 was found to be nearly five-fold higher in those children with SCA compared to Controls. Neuregulin-1β was also positively correlated with both BDNF and PDGF-AA concentrations, but was not associated with degree of anemia, suggesting that NRG-1 production may be an endogenous response to subclinical cerebral ischemia in SCA warranting further exploration.

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.

Therapeutic efficacy of neuregulin 1-expressing human adipose-derived mesenchymal stem cells for ischemic stroke

Adipose-derived mesenchymal stem cells (AdMSCs) have been reported to ameliorate neurological deficits after acute ischemic stroke. As neuregulin 1 (NRG1, or heregulin 1), a growth factor with versatile functions in the central nervous system, has demonstrated protective effects against ischemic brain injuries, we have generated NRG1-overexpressing AdMSCs in order to investigate whether NRG1-AdMSCs could enhance therapeutic benefits of AdMSCs in ischemic stroke. After AdMSCs were infected with adenoviral NRG1, increased NRG1 secretion in NRG1-AdMSCs was confirmed with ELISA. At 1 d after ischemic stroke that was induced by the occlusion of middle cerebral artery (MCAo) for 60 min in Sprague Dawley (SD) rats, adenoviral NRG1, AdMSCs, NRG1-AdMSCs, or PBS were injected into the striatum and serial neurologic examinations were performed. Administration of NRG1-AdMSCs resulted in significant improvement of functional outcome following stroke compared to AdMSCs- or adenoviral NRG1-treated group, in addition to the reduction in the infarct size evaluated by hematoxylin and eosin staining. When NRG1 expression in the brain was examined by double immunofluorescence to human nuclei (HuNu)/NRG1 and ELISA, NRG1-AdMSCs demonstrated marked increase in NRG1 expression. Moreover, western blot analysis further showed that transplantation of NRG1-AdMSCs significantly increased both endogenous and adenoviral NRG1 expression compared to AdMSCs-treated group. To elucidate molecular mechanisms, NRG1-associated downstream molecules were evaluated by western blot analysis. Expression of ErbB4, a receptor for NRG1, was markedly increased by NRG1-AdMSCs administration, in addition to pMAPK and pAkt, crucial molecules of NRG1-ErbB4 signaling. Taken together, our data suggest that NRG1-AdMSCs can provide excellent therapeutic potential in ischemic stroke by activating NRG1-ErbB4 signaling network.

A Systematic Review of Closed Head Injury Models of Mild Traumatic Brain Injury in Mice and Rats

Mild TBI (mTBI) is a significant health concern. Animal models of mTBI are essential for understanding mechanisms, and pathological outcomes, as well as to test therapeutic interventions. A variety of closed head models of mTBI that incorporate different aspects (i.e., biomechanics) of the mTBI have been reported. The aim of the current review was to compile a comprehensive list of the closed head mTBI rodent models, along with the common data elements, and outcomes, with the goal to summarize the current state of the field. Publications were identified from a search of PubMed and Web of Science and screened for eligibility following PRISMA guidelines. Articles were included that were closed head injuries in which the authors classified the injury as mild in rats or mice. Injury model and animal-specific common data elements, as well as behavioral and histological outcomes, were collected and compiled from a total of 402 articles. Our results outline the wide variety of methods used to model mTBI. We also discovered that female rodents and both young and aged animals are under-represented in experimental mTBI studies. Our findings will aid in providing context comparing the injury models and provide a starting point for the selection of the most appropriate model of mTBI to address a specific hypothesis. We believe this review will be a useful starting place for determining what has been done and what knowledge is missing in the field to reduce the burden of mTBI.

The S100A4 Protein Signals through the ErbB4 Receptor to Promote Neuronal Survival

Understanding the mechanisms of neurodegeneration is crucial for development of therapies to treat neurological disorders. S100 proteins are extensively expressed in the injured brain but S100's role and signalling in neural cells remain elusive. We recently demonstrated that the S100A4 protein protects neurons in brain injury and designed S100A4-derived peptides mimicking its beneficial effects. Here we show that neuroprotection by S100A4 involves the growth factor family receptor ErbB4 and its ligand Neuregulin 1 (NRG), key regulators of neuronal plasticity and implicated in multiple brain pathologies. The neuroprotective effect of S100A4 depends on ErbB4 expression and the ErbB4 signalling partners ErbB2/Akt, and is reduced by functional blockade of NRG/ErbB4 in cell models of neurodegeneration. We also detect binding of S100A4 with ErbB1 (EGFR) and ErbB3. S100A4-derived peptides interact with, and signal through ErbB, are neuroprotective in primary and immortalized dopaminergic neurons, and do not affect cell proliferation/motility - features which make them promising as potential neuroprotectants. Our data suggest that the S100-ErbB axis may be an important mechanism regulating neuronal survival and plasticity.

The Expression of Hippocampal NRG1/ErbB4 Correlates With Neuronal Apoptosis, but Not With Glial Activation During Chronic Cerebral Hypoperfusion

Permanent bilateral common carotid occlusion (2VO) is well-established to investigate the chronic cerebral hypoperfusion (CCH)-induced cognitive deficits. Besides, previous studies suggested that disturbance of Neuregulin1 (NRG1)/ErbB4 signaling is associated with cognitive impairments, as well as neuronal apoptosis and neuroinflammation in CNS. However, the expression pattern of hippocampal NRG1/ErbB4 has not been systematically investigated during CCH. Here, we aim to investigate the temporal changes of hippocampal NRG1/ErbB4 during CCH and their possible relationship with neuronal apoptosis and glial activation. Morris water maze (MWM) and Radial arm water maze (RAWM) tests were used to analyze cognitive impairment in 2VO rats at 28 days post-surgery, and Enzyme-Linked Immunosorbent Assay (ELISA), western blotting and immunostaining were performed at different time points (24 h, 7 days, 14 days, 28 days) to detect the expression pattern of NRG1/ErbB4 and the distribution of ErbB4. Neuronal nuclei (NeuN), NeuN/TUNEL, Iba1 and GFAP immunostaining and caspase activity in hippocampal CA1 subarea were assessed during CCH as well. We found that the expression of NRG1 and phosphorylated ErbB4 (pErbB4)/ErbB4 changed in a time-dependent manner (up-regulated in the acute phase and then decreased in the chronic phase of CCH). Besides, ErbB4-expressed neurons and selective types of GABAergic cells decreased after CCH, but the distribution pattern of ErbB4 remained unchanged. In addition, the expression of hippocampal NRG1/ErbB4 positively correlated with the level of neuronal apoptosis (both NeuN/TUNEL immunostaining and caspase-3 activity), but not with glial activation according to Pearson’s correlation. These findings indicated that hippocampal NRG1/ErbB4 may be involved in the pathogenesis of CCH, especially neuronal apoptosis during CCH.

NRG-1β exerts neuroprotective effects against ischemia reperfusion-induced injury in rats through the JNK signaling pathway

BACKGROUND

Neuregulin-1β (NRG-1β) has great potential to be developed into therapeutics for neuroprotection. The aim of the current study was to analyze the effects and possible signaling pathway of NRG-1β on brain tissues in a rat model of middle cerebral artery occlusion/reperfusion (MCAO/R).

METHODS

In order to observe the protective effect of NRG-1β on MCAO/R, the neurological deficit and infarct volume were measured using a modified neurological severity score (mNSS) test and by triphenyl tetrazolium chloride (TTC) staining. In order to detect the antagonistic effect of NRG-1β on nerve cells and the blood-brain barrier (BBB), the morphology and structure of cortical brain tissues were observed by Evans Blue (EB) staining, hematoxylin-eosin (H&E) and Nissl staining, in situ cell death detection kit, and transmission electron microscopy (TEM). In order to investigate whether NRG-1β exhibited a significant neuroprotective effect via the JNK signaling pathway, the activity of JNK and the levels of phospho-MKK4, phospho-JNK, pan-JNK and phospho-c-Jun were tested using a JNK activity screening kit, immunofluorescent labeling, and western blot analysis, respectively.

RESULTS

In the NRG-1β treatment group, accompanied with a decrease in JNK activity, the protein levels of phospho-JNK, phospho-MKK4 and phospho-c-Jun decreased, the ischemia-induced apoptosis decreased, the abnormal morphological structures of nerve cells were ameliorated, the integrity of the BBB was restored, and infarct volume was reduced. At the same time, neurological function was significantly recovered.

CONCLUSION

NRG-1β exerts a neuroprotective effect through the JNK signaling pathway in MCAO/R rats.

Acute Simian Varicella Virus Infection Causes Robust and Sustained Changes in Gene Expression in the Sensory Ganglia

Primary infection with varicella-zoster virus (VZV), a neurotropic alphaherpesvirus, results in varicella. VZV establishes latency in the sensory ganglia and can reactivate later in life to cause herpes zoster. The relationship between VZV and its host during acute infection in the sensory ganglia is not well understood due to limited access to clinical specimens. Intrabronchial inoculation of rhesus macaques with simian varicella virus (SVV) recapitulates the hallmarks of VZV infection in humans. We leveraged this animal model to characterize the host-pathogen interactions in the ganglia during both acute and latent infection by measuring both viral and host transcriptomes on days postinfection (dpi) 3, 7, 10, 14, and 100. SVV DNA and transcripts were detected in sensory ganglia 3 dpi, before the appearance of rash. CD4 and CD8 T cells were also detected in the sensory ganglia 3 dpi. Moreover, lung-resident T cells isolated from the same animals 3 dpi also harbored SVV DNA and transcripts, suggesting that T cells may be responsible for trafficking SVV to the ganglia. Transcriptome sequencing (RNA-Seq) analysis showed that cessation of viral transcription 7 dpi coincides with a robust antiviral innate immune response in the ganglia. Interestingly, a significant number of genes that play a critical role in nervous system development and function remained downregulated into latency. These studies provide novel insights into host-pathogen interactions in the sensory ganglia during acute varicella and demonstrate that SVV infection results in profound and sustained changes in neuronal gene expression.

IMPORTANCE

Many aspects of VZV infection of sensory ganglia remain poorly understood, due to limited access to human specimens and the fact that VZV is strictly a human virus. Infection of rhesus macaques with simian varicella virus (SVV), a homolog of VZV, provides a robust model of the human disease. Using this model, we show that SVV reaches the ganglia early after infection, most likely by T cells, and that the induction of a robust innate immune response correlates with cessation of virus transcription. We also report significant changes in the expression of genes that play an important role in neuronal function. Importantly, these changes persist long after viral replication ceases. Given the homology between SVV and VZV, and the genetic and physiological similarities between rhesus macaques and humans, our results provide novel insight into the interactions between VZV and its human host and explain some of the neurological consequences of VZV infection.

Differential changes in Neuregulin-1 signaling in major brain regions in a lipopolysaccharide-induced neuroinflammation mouse model

Neuregulin 1 (Nrg1) is involved in multiple biological processes in the nervous system. The present study investigated changes in Nrg1 signaling in the major brain regions of mice subjected to lipopolysaccharide (LPS)-induced neuroinflammation. At 24 h post‑intraperitoneal injection of LPS, mouse brain tissues, including tissues from the cortex, striatum, hippocampus and hypothalamus, were collected. Reverse transcription‑polymerase chain reaction was used to determine the expression of Nrg1 and its receptors, Neu and ErbB4, at the mRNA level. Western blotting was performed to determine the levels of these proteins and the protein levels of phosphorylated extracellular signal-regulated kinases (Erk)1/2 and Akt1. Immunohistochemical staining was utilized to detect the levels of pNeu and pErbB4 in these regions. LPS successfully induced sites of neuroinflammation in these regions, in which changes in Nrg1, Neu and ErbB4 at the mRNA and protein levels were identified compared with controls. LPS induced a reduction in pNeu and pErbB4 in the striatum and hypothalamus, although marginally increased pErbB4 levels were found in the hippocampus. LPS increased the overall phosphorylation of Src but this effect was reduced in the hypothalamus. Moreover, increased phosphorylation of Akt1 was found in the striatum and hippocampus. These data suggest diverse roles for Nrg1 signaling in these regions during the process of neuroinflammation.

Neuregulin-1β regulates outgrowth of neurites and migration of neurofilament 200 neurons from dorsal root ganglial explants in vitro

Neuregulin-1β (NRG-1β) signaling has multiple functions in neurons. To assess NRG-1β on neurite outgrowth and neuronal migration in vitro, organotypic dorsal root ganglion (DRG) neuronal culture model was established. Neurite outgrowth and neuronal migration were evaluated using this culture model in the presence (5nmol/L, 10nmol/L, 20nmol/L) or absence of NRG-1β. Neurofilament 200 (NF-200)-immunoreactive (IR) neurons were determined as the migrating neurons. The number of nerve fiber bundles extended from DRG explant increased significantly in the presence of NRG-1β (5nmol/L, 23.0±2.2, P<0.05; 10nmol/L, 27.0±2.7, P<0.001; 20nmol/L, 30.8±3.7, P<0.001) as compared with that in the absence of NRG-1β (19.0±2.2). The number of neurons migrating from DRG explants increased significantly in the presence of NRG-1β (5nmol/L, 39.6±5.0, P<0.05; 10nmol/L, 54.6±6.7, P<0.001; 20nmol/L, 62.2±5.7, P<0.001) as compared with that in the absence of NRG-1β (31.6±4.0). Moreover, the increase of the number of nerve fiber bundles and the number of migrating NF-200-IR neurons was dose-dependent for NRG-1β addition. The data in this study imply that NRG-1β promotes neurite outgrowth and neuronal migration from DRG explants in vitro.

Phosphacan and receptor protein tyrosine phosphatase β expression mediates deafferentation-induced synaptogenesis

This study documents the spatial and temporal expression of three structurally related chondroitin sulfated proteoglycans (CSPGs) during synaptic regeneration induced by brain injury. Using the unilateral entorhinal cortex (EC) lesion model of adaptive synaptogenesis, we documented mRNA and protein profiles of phosphacan and its two splice variants, full length receptor protein tyrosine phosphatase β (RPTPβ) and the short transmembrane receptor form (sRPTPβ), at 2, 7, and 15 days postlesion. We report that whole hippocampal sRPTPβ protein and mRNA are persistently elevated over the first two weeks after UEC. As predicted, this transmembrane family member was localized adjacent to synaptic sites in the deafferented neuropil and showed increased distribution over that zone following lesion. By contrast, whole hippocampal phosphacan protein was not elevated with deafferentation; however, its mRNA was increased during the period of sprouting and synapse formation (7d). When the zone of synaptic reorganization was sampled using molecular layer/granule cell (ML/GCL) enriched dissections, we observed an increase in phosphacan protein at 7d, concurrent with the observed hippocampal mRNA elevation. Immunohistochemistry also showed a shift in phosphacan distribution from granule cell bodies to the deafferented ML at 2 and 7d postlesion. Phosphacan and sRPTPβ were not colocalized with glial fibrillary acid protein (GFAP), suggesting that reactive astrocytes were not a major source of either proteoglycan. While transcript for the developmentally prominent full length RPTPβ was also increased at 2 and 15d, its protein was not detected in our adult samples. These results indicate that phosphacan and RPTPβ splice variants participate in both the acute degenerative and long-term regenerative phases of reactive synaptogenesis. These results suggest that increase in the transmembrane sRPTPβ tyrosine phosphatase activity is critical to this plasticity, and that local elevation of extracellular phosphacan influences dendritic organization during synaptogenesis.

Neuregulin-1 regulates the expression of Akt, Bcl-2, and Bad signaling after focal cerebral ischemia in rats

Neuregulin-1 (NRG-1) is a member of the epidermal growth factor family. Our previous study showed that NRG-1 protected neurons from apoptosis following focal cerebral ischemia by the inhibition of caspase-3 and TNF-alpha expression. However, the molecular signaling mechanisms for this action of NRG-1 following cerebral ischemia are not fully understood. Presently, activation of the PI3K/Akt pathway has been implicated as a major contributor to neuronal survival after an ischemic insult. In the present study, we investigated whether NRG-1 modulates the activation of Akt and its downstream targets Bad and Bcl-2 expression after transient focal cerebral ischemia by intraluminal blockade of the middle cerebral artery. Western blot was employed to analyze the change of phosphorylated Akt (p-Akt) expression; reverse transcription and polymerization chain reaction (RT-PCR) were used to measure changes of Bcl-2 mRNA. The level of phosphorylation of Bad (p-Bad) was determined using an enzyme-linked immunosorbent assay (ELISA). Our results showed that recombinant human NRG-1(3.0 ng.kg-1) significantly increased the expression of p-Akt protein, Bcl-2 mRNA, and the level of p-Bad, respectively, whereas administration of LY294002, a specific inhibitor of PI3K, significantly decreased the expression of p-Akt, p-Bad, and Bcl-2 induced by NRG-1 after a 60 min ischemic insult, followed by 24 h of reperfusion. These results indicate that NRG-1 may be involved in regulating the expression of Bcl-2 and p-Bad through the PI3K/Akt pathway after transient focal cerebral ischemia.

Increased expression of the gamma-secretase components presenilin-1 and nicastrin in activated astrocytes and microglia following traumatic brain injury

Gamma-secretase is an aspartyl protease composed of four proteins: presenilin (PS), nicastrin (Nct), APH1, and PEN2. These proteins assemble into a membrane complex that cleaves a variety of substrates within the transmembrane domain. The gamma-secretase cleavage products play an important role in various biological processes such as embryonic development and Alzheimer's disease (AD). The major role of gamma-secretase in brain pathology has been linked to AD and to the production of the amyloid beta-peptide. However, little is known about the possible role of gamma-secretase following acute brain insult. Here we examined by immunostaining the expression patterns of two gamma-secretase components, PS1 and Nct, in three paradigms of brain insult in mice: closed head injury, intracerebroventricular injection of LPS, and brain stabbing. Our results show that in naïve and sham-injured brains expression of PS1 and Nct is restricted mainly to neurons. However, following insult, the expression of both proteins is also observed in nonneuronal cells, consisting of activated astrocytes and microglia. Furthermore, the proteins are coexpressed within the same astrocytes and microglia, implying that these cells exhibit an enhanced gamma-secretase activity following brain damage. In view of the important role played by astrocytes and microglia in brain disorders, our findings suggest that gamma-secretase may participate in brain damage and repair processes by regulating astrocyte and microglia activation and/or function.

Neuregulin-1 attenuates neointimal formation following vascular injury and inhibits the proliferation of vascular smooth muscle cells

Neuregulin-1 (NRG-1) is expressed in vascular endothelial cells, and its receptors are localized to the underlying smooth muscle cells. However, the role of NRG-1 in vascular function and injury is largely unknown. First, the expression of NRG-1 and its receptors (erbB receptors) was analyzed after balloon injury to the rat carotid artery. NRG-1 and erbB expression levels were low in uninjured vessels; however, NRG-1 and erbB4 were upregulated following injury. We then examined the effect of NRG-1 on neointimal formation following balloon injury. NRG-1 was administered by tail-vein injection prior to injury and every 2 days following injury. Two weeks after injury, NRG-1-treated animals demonstrated a 50% reduction in lesion size compared with controls receiving the vehicle. To examine possible mechanisms for NRG-1 action, we examined its effects on vascular smooth muscle cell (VSMC) function. Rat VSMC cultures were pretreated with NRG-1 for 24 h and then stimulated with platelet-derived growth factor. NRG-1 significantly decreased platelet-derived growth factor-stimulated VSMC proliferation and migration. These findings suggest that NRG-1 may be a novel therapeutic candidate for the treatment of restenosis and atherosclerosis.

Rapamycin is a neuroprotective treatment for traumatic brain injury

The mammalian target of rapamycin, commonly known as mTOR, is a serine/threonine kinase that regulates translation and cell division. mTOR integrates input from multiple upstream signals, including growth factors and nutrients to regulate protein synthesis. Inhibition of mTOR leads to cell cycle arrest, inhibition of cell proliferation, immunosuppression and induction of autophagy. Autophagy, a bulk degradation of sub-cellular constituents, is a process that keeps the balance between protein synthesis and protein degradation and is induced upon amino acids deprivation. Rapamycin, mTOR signaling inhibitor, mimics amino acid and, to some extent, growth factor deprivation. In the present study we examined the effect of rapamycin, on the outcome of mice after brain injury. Our results demonstrate that rapamycin injection 4 h following closed head injury significantly improved functional recovery as manifested by changes in the Neurological Severity Score, a neurobehavioral testing. To verify the activity of the injected rapamycin, we demonstrated that it inhibits p70S6K phosphorylation, reduces microglia/macrophages activation and increases the number of surviving neurons at the site of injury. We therefore suggest that rapamycin is neuroprotective following traumatic brain injury and as a drug used in the clinic for other indications, we propose that further studies on rapamycin should be conducted in order to consider it as a novel therapy for traumatic brain injury.

Neuroprotective effects of neuregulin-1 in rat models of focal cerebral ischemia

The purpose of this study was to investigate the therapeutic efficacy and mechanism of recombinant human NRG-1 to attenuate ischemia/reperfusion brain injury. NRG-1(3.0 ng/kg) was applied intravascularly 10 min before middle cerebral artery occlusion (MCAO) and then focal cerebral ischemia for 90 min and reperfusion for 24 h. The rats were scored post-reperfusion for neurological deficits and infarct volume in the brain was assessed by 2,3,5-triphenyltetrazolium chloride(TTC). Apoptosis was evaluated by TUNEL staining. Reverse transcription polymerase chain reaction (RT-PCR) was used to measure changes of caspase-3 mRNA. The level of TNF-alpha was determined using enzyme-linked immunosorbent assay (ELISA). Our results demonstrated that recombinant human NRG-1 could reduce cerebral infarct volume by about 71% (P < 0.05) and TUNEL positive cells when given immediately before MCAO, and improved behavior of animals. Furthermore, we also showed that NRG-1 could also decrease the expression of caspase-3 mRNA and production of TNF-alpha protein. These data suggest that pre-administration of NRG-1 attenuates cerebral ischemia and reperfusion injury. This protective effect may be involved in the inhibition of caspase-3 and TNF-alpha.

Transforming growth factor alpha acts as a gliatrophin for mouse and human astrocytes

Astrocyte death has been implicated in several neuropathological diseases, but the identification of molecules susceptible of promoting astrocyte survival has been elusive. We investigated whether transforming growth factor alpha (TGFalpha), an erbB1/EGFR ligand, which promotes glioma progression and affects astrocyte metabolism at embryonic and adult stages, regulates astrocyte survival. Primary serum-free astrocyte cultures from post-natal mouse and fetal human cortices were used. Transforming growth factor alpha protected both species of astrocytes from staurosporine-induced apoptosis. In serum-free medium, mouse astrocytes did not survive beyond 2 months while TGFalpha-treated astrocytes survived up to 12 months. Transforming growth factor alpha also promoted long-term survival of human astrocytes. We additionally extended TGFalpha proliferative effects to human astrocytes. After 3 days of permanent application, TGFalpha induced a major downregulation of both erbB1 and erbB2. This downregulation did not impair the functional activation of the receptors, as ascertained by their tyrosine phosphorylation and the continuous stimulation of both ERK/MAPK and PI3K/Akt pathways up to 7 days, the longest time examined. The full cellular effects of TGFalpha required activation of both transduction pathways. Enhanced proliferation and survival thus define TGFalpha as a gliatrophin for mammalian astrocytes. These results demonstrate that in normal, non-transformed astrocytes, sustained and functional erbBs activation is achieved without bypassing ligand-induced receptors downregulation.

Closed head injury induces upregulation of Beclin 1 at the cortical site of injury

Autophagy, a bulk degradation of subcellular constituents, is activated in several neurodegenerative conditions. Beclin 1, a Bcl2 interacting protein, was found to promote autophagy. The closed head injury model was used to investigate the possible role of autophagy and Beclin 1 after traumatic brain injury. It is demonstrated that levels of Beclin-1 are dramatically increased near the site of injury. Neurons constitute the major population of cells, with the highest Beclin 1 levels near the site of injury at early stages post injury. Elevated levels of Beclin 1 protein in neurons last for at least 3 weeks. In addition, Beclin-1 expression after injury is elevated also in astrocytes starting at 3 days after injury. Confocal microscopy analysis suggests that the high levels of Beclin 1 protein in astrocytes is confined to subcellular organelles, probably lysosomes or autophagosomes. Double staining of Beclin 1 and TUNEL indicate that most of the injured cells that exhibit double staining are neurons and not astrocytes. These findings show that Beclin 1 may play a role in brain responses to head trauma. Overexpression of Beclin 1 may be important for autophagy at the lesion site and may serve as a mechanism to discard injured cells and reduce damage to cells by disposing of injured components.

Neuregulin-1 increases the proliferation of neuronal progenitors from embryonic neural stem cells

Neuregulins are a family of proteins expressed in the developing brain and in brain regions that continue to undergo neurogenesis in adult animals. We investigated the effects of neuregulins on embryonic neural stem cells (NSCs) isolated from E11 mouse telencephalon. Treatment of basic fibroblast growth factor (bFGF)-expanded neurosphere cultures with the EGF-like domain of neuregulin1-beta1 (NRG-1(177-244)) resulted in a 4-fold increase of bromodeoxyuridine (BrDU)-labeled cells, suggesting that NRG-1 stimulated proliferation. The majority of the BrdU-positive cells co-labeled with an antibody against MAP2, indicating that the proliferating cells were neuronal. No BrDU labeling was seen in GFAP- or O4-positive cells. In NRG-1-treated cultures, many of the MAP2-positive cells co-labeled with an anti-nestin antibody, suggesting that these cells are neuron-restricted progenitors (NRPs). Few MAP2/nestin-positive cells were seen in control cultures. The increase in the number of neuronal cells in NRG-1-treated cultures was due to increased proliferation of MAP2-positive cells rather than the regulation of cell survival or fate determination. These results suggest that neuregulins are mitogenic to NRPs, thus endogenous neuregulins may play important roles during CNS neurogenesis.

Upregulation of erbB receptors in rat brain after middle cerebral arterial occlusion

We have previously demonstrated that neuregulin-1 (NRG-1) is upregulated and is neuroprotective in ischemic brain injury, however the expression and localization of its receptors during ischemia has not been investigated. Therefore, we used a rat middle cerebral artery occlusion (MCAO) model to examine the distribution of erbB receptors following ischemic stroke. Like neuregulin-1, we observed a dramatic induction of erbB4 in the peri-infarct regions of the ipsilateral cortex 24 h following MCAO. Using Fluoro-Jade B (FJB) staining as a marker of neurodegeneration, erbB4 was upregulated in FJB-positive cells, suggesting that erbB receptors are induced in injured neurons. The increase in erbB receptors was seen in neurons and a subpopulation of macrophages/microglia. There was no erbB co-localization with GFAP-positive astrocytes. These results demonstrate that erbB receptors are upregulated in neurons and macrophages/microglia following ischemic stroke and may be involved in neuroprotection and repair.

ErbB transmembrane tyrosine kinase receptors are expressed by sensory and motor neurons projecting into sciatic nerve

Adult spinal cord motor and dorsal root ganglion (DRG) sensory neurons express multiple neuregulin-1 (NRG-1) isoforms that act as axon-associated factors promoting neuromuscular junction formation and Schwann cell proliferation and differentiation. NRG-1 isoforms are also expressed by muscle and Schwann cells, suggesting that motor and sensory neurons are themselves acted on by NRG-1 isoforms produced by their peripheral targets. To test this hypothesis, we examined the expression of the NRG-1 receptor subunits erbB2, erbB3, and erbB4 in rat lumbar DRG and spinal cord. All three erbB receptors are expressed in these tissues. Sciatic nerve transection, an injury that induces Schwann cell expression of NRG-1, alters erbB expression in DRG and cord. Virtually all DRG neurons are erbB2- and erbB3-immunoreactive, with erbB4 also detectable in many neurons. In spinal cord white matter, erbB2 and erbB4 antibodies produce dense punctate staining, whereas the erbB3 antibody primarily labels glial cell bodies. Spinal cord dorsal and ventral horn neurons, including alpha-motor neurons, exhibit erbB2, erbB3, and erbB4 immunoreactivity. Spinal cord ventral horn also contains a population of small erbB3+/S100beta+/GFAP- cells (GFAP-negative astrocytes or oligodendrocytes). We conclude that sensory and motor neurons projecting into sciatic nerve express multiple erbB receptors and are potentially NRG-1 responsive.

Neuregulin-1 is neuroprotective and attenuates inflammatory responses induced by ischemic stroke

Recent work from our laboratory demonstrated that the expression neuregulin-1 in neurons was induced in the ischemic penumbra by focal stroke in the rat. Here, we show that a single intravascular injection of neuregulin-1beta (approximately 2.5 ng/kg) reduced cortical infarct volume by >98% when given immediately before middle cereral artery occlusion. Subcortical infarct volume was reduced by approximately 40%. Analysis of DNA fragmentation in brain tissues indicated that neuregulin-1 blocked apoptosis in cortical neurons in the penumbra. Neuregulin-1 prevented macrophage/microglial infiltration and astrocytic activation following focal ischemia. The neuroprotective effect of neuregulin-1 was also associated with a suppression of interleukin-1beta mRNA levels. These data suggest that neuregulin-1 protects neurons from delayed, ischemia-induced apoptotic cell death in the cortex by inhibiting pro-inflammatory responses. Neuregulins represent a novel, potent neuroprotective strategy that has potential therapeutic value in treating individuals after acute ischemic stroke.

Neuregulin-1 reduces ischemia-induced brain damage in rats

Neuregulin-1 (NRG-1) is expressed throughout the immature and adult central nervous system and it has been demonstrated to influence the migration of a variety of cell types in developing brain. Elevated levels of NRG-1 transcript are found in the adult brain after injury, leading to the suggestion that NRG-1 is involved in the physiological response to neuronal injury. Here, we report our findings that rats pre-treated with NRG-1 protein, undergoing cerebral ischemia 30 min later, had increased motor performance and less cerebral infarction than untreated rats. In the cortex of NRG-1 treated rats, ischemia induced a decrease in caspase-3 immunoreactivity and a reduction in the density of cells positive for terminal deoxynucleotidyl transferase-mediated dUTP-biotin in situ nick end-labeling. Improvement in behavioral assays was also found in animals treated with NRG-1. Pre-treatment with NRG-1 did not alter cerebral blood flow or other physiological parameters. NRG-1 reduced ischemia/reperfusion injury, indicating that it may act as an endogenous neuroprotective factor against stroke. Therefore, NRG-1 may represent a target for the development of new treatments for stroke.

Apolipoprotein e4 decreases whereas apolipoprotein e3 increases the level of secreted amyloid precursor protein after closed head injury

Apolipoprotein E (apoE4) and head trauma are important genetic and environmental risk factors for Alzheimer's disease. Furthermore, apoE4 increases both the acute and chronic consequences of head trauma. The latter are associated with the deposition of amyloid-beta, which is particularly elevated in apoE4 subjects. The short-term effects of head injury are associated with transiently increased metabolism of amyloid precursor protein (APP) and its secreted fragment, APPs. In the present study, we examined the possibility that the acute, short-term pathological effects of apoE4 following head trauma and the corresponding neuroprotective effects of apoE3 are related to isoform-specific effects of apoE on APP metabolism. Accordingly, male transgenic mice expressing human apoE3 or apoE4 on a null mouse apoE background and apoE-deficient and control mice were subjected to closed head injury (CHI). The resulting effects on brain APP, and on its secreted products, APPs and secreted product of the alpha-cleavage of APP (APPsalpha) were then determined 24 h following injury. Immunoblotting revealed no significant differences between the basal APP, APPs and APPsalpha levels of the hippocampus or the cortex of the control and the apoE3 and ApoE4 transgenic mice. The apoE-deficient mice also had similar cortical basal levels of APP and its metabolites, whereas their corresponding basal hippocampal APP and APPs levels were lower than those of the other groups. CHI lowered the hipppocampal APPs and APPsalpha levels of the apoE4 transgenic mice, whereas those of the apoE3 transgenic mice and of the control and apoE-deficient mice were not affected by this insult. In contrast, CHI raised the cortical APP and APPs levels of the apoE3 transgenic mice but had no significant effect on those of the other mice groups. These animal model findings suggest that the acute, short-term pathological effects of apoE4 following CHI and the corresponding neuroprotective effects of apoE3 may be mediated by their opposing effects on the expression and cleavage of cortical and hippocampal APP. Similar isoform-specific interactions between apoE and APP may play a role in the acute, short-term effects of head trauma in humans.

The neuregulin GGF2 attenuates free radical release from activated microglial cells

The neuregulin glial growth factor 2 (GGF2) is a neural growth factor that is best known for its ability to promote the survival and proliferation of oligodendrocytes and Schwann cells. While it has been shown in recent years that GGF2 is effective in the treatment of autoimmune models of brain injury, it is not known if the beneficial effects of GGF2 are based in part on modulation of brain inflammation. In this report, we document the anti-inflammatory effects of recombinant human GGF2 (rhGGF2) on microglial free radical production in vitro. The presence of the neuregulin receptors ErbB2, 3, and 4 was confirmed in N9 microglial cells by Western blot analysis. Pretreatment of N9 cells with 10-100 ng/ml rhGGF2 24 h before either phorbol 12-myristate 3-acetate (PMA) or interferon gamma (IFNgamma) caused dose-dependent decreases in oxidative burst activity and nitrite release, respectively, with 50 and 100 ng/ml causing significant effects. When cells were co-treated with increasing doses of rhGGF2 and PMA or IFNgamma, only concentrations of 50 ng/ml, but not 10 or 100 ng/ml, were able to decrease oxidative burst activity and nitrite release. Finally, when microglial cell viability following treatment of cells with IFNgamma with or without rhGGF2 was evaluated, it was observed that 50 and 100 ng/ml rhGGF2 conferred significant protection against IFNgamma-induced cell death in microglial cells. Overall, these results indicate that the neuregulin rhGGF2 may have anti-inflammatory and antioxidant properties in the brain, and may also provide trophic support for brain-resident microglial cells.

Neuregulin-1 and erbB4 immunoreactivity is associated with neuritic plaques in Alzheimer disease brain and in a transgenic model of Alzheimer disease

Neuregulin-1 (NRG-1) regulates developmental neuronal survival and synaptogenesis, astrocytic differentiation, and microglial activation. Given these NRG-1 actions, we hypothesized that the synaptic loss, gliosis, inflammation, and neuronal death occurring in Alzheimer disease (AD) is associated with altered expression of NRG-1 and its receptors (the erbB2, erbB3, and erbB4 membrane tyrosine kinases). We examined the expression and distribution of NRG-1 and the erbB kinases in the hippocampus of AD patients and cognitively normal controls and in transgenic mice that coexpress AD-associated mutations of the beta amyloid precursor protein (APP(K670N,M671L)) and presenilin-1 (PS1(M146L)). In the hippocampi of both control humans and wild type mice, NRG-1 and the 3 erbB receptors are expressed in distinct cellular compartments of hippocampal neurons. All 4 molecules are associated with neuronal cell bodies, but only NRG-1, erbB2, and erbB4 are present in synapse-rich regions. In AD and in the doubly transgenic mouse, erbB4 is expressed by reactive astrocytes and microglia surrounding neuritic plaques. In AD brains, microglia and, to a lesser extent, dystrophic neurites, also upregulate NRG-1 in neuritic plaques, suggesting that autocrine and/or paracrine interactions regulate NRG-1 action within these lesions. NRG-1 and erbB4, as well as erbB2, are similarly associated with neuritic plaques in the doubly transgenic mice. Thus, in AD the hippocampal distribution of NRG-1 and erbB4 is altered. The similarities between the alterations in the expression of NRG-1 and its receptors in human AD and in APP(K670N;M671L)/PS1(M146L) mutant mice suggests that this animal model may be very informative in deciphering the potential role of these molecules in AD.

Neuregulin expression after focal stroke in the rat

Upregulation of neuregulin has been demonstrated in traumatic brain injury, but a role for neuregulin in ischemic brain injury has not been investigated. Therefore, we used a rat permanent middle cerebral artery occlusion model to examine the distribution of neuregulin after the onset of ischemic stroke. We found an increase in immunohistochemical staining for neuregulin in the penumbral regions of the cortex. The increase in neuregulin appeared to be neuronal. There was no neuregulin co-localization with astrocytes or macrophages. These results demonstrate that neuregulin is induced in neurons following ischemic stroke and may be involved in neuroprotection and repair.

Prolonged intrathecal release of soluble Fas following severe traumatic brain injury in humans

The mechanisms underlying cell death following traumatic brain injury (TBI) are not fully understood. Apoptosis is believed to be one mechanism contributing to a marked and prolonged neuronal cell loss following TBI. Recent data suggest a role for Fas (APO-1, CD95), a type I transmembrane receptor glycoprotein of the nerve growth factor/tumor necrosis factor superfamily, and its ligand (Fas ligand, FasL) in apoptotic events in the central nervous system. A truncated form of the Fas receptor, soluble Fas (sFas) may indicate activation of the Fas/FasL system and act as a negative feedback mechanism, thereby inhibiting Fas mediated apoptosis. Soluble Fas was measured in cerebrospinal fluid (CSF) and serum of 10 patients with severe TBI (GCS< or =8) for up to 15 days post-trauma. No sFas was detected in CSF samples from patients without neurological pathologies. Conversely, after TBI 118 out of 120 CSF samples showed elevated sFas concentrations ranging from 56 to 4327 mU/ml. Paired serum samples showed above normal (8.5 U/ml) sFas concentrations in 5 of 10 patients. Serum levels of sFas were always higher than CSF levels. However, there was no correlation between concentrations measured in CSF and in serum (r(2)=0.078, p=0.02), suggesting that the concentrations in the two compartments are independently regulated. Also, no correlation was found between sFas in CSF and blood brain barrier (BBB) dysfunction as assessed by the albumin CSF/serum quotient (Q(A)), and concentrations of the cytotoxic cytokine tumor necrosis factor-alpha in CSF, respectively. Furthermore, there was no correlation with two markers of immune activation (soluble interleukin-2 receptor and neopterin) in CSF. Maximal CSF levels of sFas correlated significantly (r(2)=0.8191, p<0.001) with the early peaks of neuron-specific enolase in CSF (a marker for neuronal cell destruction), indicating that activation of the Fas mediated pathway of apoptosis may be in part the direct result of the initial trauma. However, the prolonged elevation of sFas in CSF may be caused by the ongoing inflammatory response to trauma and delayed apoptotic cell death.

Neuregulin rescues PC12-ErbB4 cells from cell death induced by H(2)O(2). Regulation of reactive oxygen species levels by phosphatidylinositol 3-kinase

Neuregulins (NRGs), a large family of transmembrane polypeptide growth factors, mediate various cellular responses depending on the cell type and receptor expression. We previously showed that NRG mediates survival of PC12-ErbB4 cells from apoptosis induced by serum deprivation or tumor necrosis factor-alpha treatment. In the present study we show that NRG induces a significant protective effect from H(2)O(2)-induced death. This effect of NRG is mediated by the phosphatidylinositol 3-kinase (PI3K)-signaling pathway since NRG failed to rescue cells from H(2)O(2) insult in the presence of the PI3K inhibitor, LY294002. Furthermore, the downstream effector of PI3K, protein kinase B/AKT, is activated by NRG in the presence of H(2)O(2), and protein kinase B/AKT activation is inhibited by LY294002. In addition, our results demonstrate that reactive oxygen species (ROS) elevation induced by H(2)O(2) is inhibited by NRG. LY294002, which blocks NRG-mediated rescue, increases ROS levels. Moreover, both H(2)O(2)-induced ROS elevation and cell death are reduced by expression of activated PI3K. These results suggest that PI3K-dependent pathways may regulate toxic levels of ROS generated by oxidative stress.