Distinct isoforms of neuregulin are expressed in mesenchymal and neuronal cells during mouse development

Neuregulin 1 (NRG1) and its receptors in the enteric nervous system and other parts of the gastrointestinal wall

Neuregulin 1 (NRG1) belonging to the transmembrane growth factors family is widespread in living organisms. It acts through ErbB family receptors and first of all takes part in embryogenesis, as well as in developmental, regenerative and adaptive processes occurring in various internal organs and systems. It is known that NRG1 and its receptors are present in various parts of the gastrointestinal (GI) tract. First of all NRG1 and ErbB receptors have been detected in the enteric nervous system (ENS) localized in the wall of the esophagus, stomach and intestine and regulating the majority of the GI tract functions, but also in the mucosal and muscular layers of the GI tract. The NRG1/ErbB pathway is involved in the development and differentiation of the ENS and regulation of the intestinal epithelium functions. Moreover, dysregulation of this pathway results in a wide range of gastrointestinal diseases. However, till now there are no summarizations of previous studies concerning distribution and functions of NRG1 and its receptors in the GI tract. The present review fills this gap.

Epidermal growth factor receptors and their ligands are expressed in the spleen of the Japanese Quail (Coturnix coturnix japonica) during the post-hatch period

1. The epidermal growth factor (EGF) family plays an important role in the development, differentiation, migration and apoptosis of cells, as well as in wound healing, which are all essential to the viability of multicellular organisms. The avian spleen is a principal organ of systemic immunity and its importance in disease resistance is presumably accentuated by the scarcity of avian lymph nodes.2. The aim of this study was to determine whether EGF receptors (ErbB1-4) and their ligands (EGF, AREG and NRG) are expressed in the structural components of the quail spleen during the post-hatch period. At each selected age, from 1 d to 7, 14, 21 and 60 d, 10 quails were euthanised under ether anaesthesia and their spleens were fixed in a 10% formaldehyde-alcohol solution. Following routine histological processing, the streptavidin-biotin-peroxidase method was used for immunohistochemical examination.3. Strong cytoplasmic immunoreactions for ErbB2, ErbB4 and NRG were observed in the ellipsoid associated cells (EAC) of the quail spleen throughout the post-hatch period. This immunoreactivity in the EAC increased after the 7th d post-hatch. ErbB1 and ErbB3 immunoreactions were relatively similar and weak in all components of the spleen during the post-hatch period. Some immune cells of the peri-arterial lymphatic sheath (PALS) and peri-ellipsoidal lymphatic sheath (PELS) showed positive immunoreactivity for the ErbB receptors and their ligands. In the vascular smooth muscle cells, immunoreactivity for ErbB2 was stronger than that for the other ErbB receptors and their ligands.4. The data showed that ErbB receptors and their ligands (EGF, AREG and NRG) are expressed by different structural components of the quail spleen during the post-hatch period.

Investigating mutations at the hotspot position of the ERBB2 and screening for the novel lead compound to treat breast cancer - a computational approach

Membrane proteins are the most common types of cancer that are active in the prognosis. Membrane proteins are a distinguishing characteristic of a cancer cell. In tumor cell therapy, the overexpressed membrane proteins are becoming ever more relevant. The 3-kinase (PI3K)/AKT phosphatidylinositol pathway is downstream triggered by different extracellular signals, and this signaling pathway activation impacts a variety of proliferation of the cellular processes like cell growth and surviving. Frequent PI3K/AKT dysregulation in human cancer has rendered proteins of this pathway desirable for diagnostic markers. Members of the ERBB family-like ERBB2 and ERBB3 activate intracellular signaling pathways such as PI3K/AKT. The mutations in these proteins dysfunctions the proteins in the downstream. Considering this importance, we have developed a computational pipeline to identify the mutation position with a highest number of mutations and to screen them for pathogenicity, stability, conservation, and structural changes using PredictSNP, iStable, ConSurf, and GROMACS simulation software respectively. Further, a virtual screening approach was initiated to find the most similar non-toxic lead compound, which could be an alternative to the currently used lapatinib. To conclude, protein-ligand dynamics were undertaken to study the actions of native and mutants with the lapatinib and the lead compound. From the overall analysis, we identified position 755 with leucine in the native condition is prone to frequent mutations. The leucine at 755th position is more prone to mutate as serine and tryptophan. Further from the computational analysis, we identified that the mutation L755S is more significant than the L755W mutation. We have witnessed CID140590176 be a potential lead compound with no toxicity. The behavior of the lead compound has shown more compactness with an increased number of intermolecular hydrogen bonds in the ERBB2 with L755S. This lead compound can be further taken for experimental validations, and we believe that this lead compound could be a potent ERBB2 inhibitor.

Temporal Dynamics of the Neuregulin-ErbB Network in the Murine Prefrontal Cortex across the Lifespan

Neuregulin-ErbB signaling is essential for numerous functions in the developing, adult, and aging brain, particularly in the prefrontal cortex (PFC). Mouse models with disrupted Nrg and/or ErbB genes are relevant to psychiatric, developmental, and age-related disorders, displaying a range of abnormalities stemming from cortical circuitry impairment. Many of these models display nonoverlapping phenotypes dependent upon the gene target and timing of perturbation, suggesting that cortical expression of the Nrg-ErbB network undergoes temporal regulation across the lifespan. Here, we report a comprehensive temporal expression mapping study of the Nrg-ErbB signaling network in the mouse PFC across postnatal development through aging. We find that Nrg and ErbB genes display distinct expression profiles; moreover, splice isoforms of these genes are differentially expressed across the murine lifespan. We additionally find a developmental switch in ErbB4 splice isoform expression potentially mediated through coregulation of the lncRNA Miat expression. Our results are the first to comprehensively and quantitatively map the expression patterns of the Nrg-ErbB network in the mouse PFC across the postnatal lifespan and may help disentangle the pathway's involvement in normal cortical sequences of events across the lifespan, as well as shedding light on the pathophysiological mechanisms of abnormal Nrg-ErbB signaling in neurological disease.

Functions of 'A disintegrin and metalloproteases (ADAMs)' in the mammalian nervous system

'A disintegrin and metalloproteases' (ADAMs) are a family of transmembrane proteins with diverse functions in multicellular organisms. About half of the ADAMs are active metalloproteases and cleave numerous cell surface proteins, including growth factors, receptors, cytokines and cell adhesion proteins. The other ADAMs have no catalytic activity and function as adhesion proteins or receptors. Some ADAMs are ubiquitously expressed, others are expressed tissue specifically. This review highlights functions of ADAMs in the mammalian nervous system, including their links to diseases. The non-proteolytic ADAM11, ADAM22 and ADAM23 have key functions in neural development, myelination and synaptic transmission and are linked to epilepsy. Among the proteolytic ADAMs, ADAM10 is the best characterized one due to its substrates Notch and amyloid precursor protein, where cleavage is required for nervous system development or linked to Alzheimer's disease (AD), respectively. Recent work demonstrates that ADAM10 has additional substrates and functions in the nervous system and its substrate selectivity may be regulated by tetraspanins. New roles for other proteolytic ADAMs in the nervous system are also emerging. For example, ADAM8 and ADAM17 are involved in neuroinflammation. ADAM17 additionally regulates neurite outgrowth and myelination and its activity is controlled by iRhoms. ADAM19 and ADAM21 function in regenerative processes upon neuronal injury. Several ADAMs, including ADAM9, ADAM10, ADAM15 and ADAM30, are potential drug targets for AD. Taken together, this review summarizes recent progress concerning substrates and functions of ADAMs in the nervous system and their use as drug targets for neurological and psychiatric diseases.

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.

Gonadotropin-Dependent Neuregulin-1 Signaling Regulates Female Rat Ovarian Granulosa Cell Survival

Mammalian ovarian follicular development and maturation of an oocyte competent to be fertilized and develop into an embryo depends on tightly regulated, spatiotemporally orchestrated crosstalk among cell death, survival, and differentiation signals through extra- and intraovarian signals, as well as on a permissive ovarian follicular microenvironment. Neuregulin-1 (NRG1) is a member of the epidermal growth factor-like factor family that mediates its effects by binding to a member of the erythroblastoma (ErbB) family. Our experimental results suggest gonadotropins promote differential expression of NRG1 and erbB receptors in granulosa cells (GCs), and NRG1 in theca cells during follicular development, and promote NRG1 secretions in the follicular fluid (FF) of rat ovaries. During the estrous cycle of rat, NRG1 and erbB receptors are differentially expressed in GCs and correlate positively with serum gonadotropins and steroid hormones. Moreover, in vitro experimental studies suggest that the protein kinase C inhibitor staurosporine (STS) causes the physical destruction of GCs by the activation of caspase-3. Exogenous NRG1 treatment of GCs delayed onset of STS-induced apoptosis and inhibited cleaved caspase-3 expressions. Moreover, exogenous NRG1 treatment of GCs alters STS-induced death by maintaining the expression of ErbB2, ErbB3, pAkt, Bcl2, and BclxL proteins. Taken together, these studies demonstrate that NRG1 is gonadotropin dependent, differentially regulated in GCs and theca cells, and secreted in ovarian FF as an intracellular survival factor that may govern follicular maturation.

Structural Similarities between Neuregulin 1-3 Isoforms Determine Their Subcellular Distribution and Signaling Mode in Central Neurons

The Neuregulin (NRG) family of ErbB ligands is comprised of numerous variants originating from the use of different genes, alternative promoters, and splice variants. NRGs have generally been thought to be transported to axons and presynaptic terminals where they signal via ErbB3/4 receptors in paracrine or juxtacrine mode. However, we recently demonstrated that unprocessed pro-NRG2 accumulates on cell bodies and proximal dendrites, and that NMDAR activity is required for shedding of its ectodomain by metalloproteinases. Here we systematically investigated the subcellular distribution and processing of major NRG isoforms in rat hippocampal neurons. We show that NRG1 isotypes I and II, which like NRG2 are single-pass transmembrane proteins with an Ig-like domain, share the same subcellular distribution and ectodomain shedding properties. We furthermore show that NRG3, like CRD-NRG1, is a dual-pass transmembrane protein that harbors a second transmembrane domain near its amino terminus. Both NRG3 and CRD-NRG1 cluster on axons through juxtacrine interactions with ErbB4 present on GABAergic interneurons. Interestingly, although single-pass NRGs accumulate as unprocessed proforms, axonal puncta of CRD-NRG1 and NRG3 are comprised of processed protein. Mutations of CRD-NRG1 and NRG3 that render them resistant to BACE cleavage, as well as BACE inhibition, result in the loss of axonal puncta and in the accumulation of unprocessed proforms in neuronal soma. Together, these results define two groups of NRGs with distinct membrane topologies and fundamentally different targeting and processing properties in central neurons. The implications of this functional diversity for the regulation of neuronal processes by the NRG/ErbB pathway are discussed.SIGNIFICANCE STATEMENT Numerous Neuregulins (NRGs) are generated through the use of different genes, promoters, and alternative splicing, but the functional significance of this evolutionary conserved diversity remains poorly understood. Here we show that NRGs can be categorized by their membrane topologies. Single-pass NRGs, such as NRG1 Types I/II and NRG2, accumulate as unprocessed proforms on cell bodies, and their ectodomains are shed by metalloproteinases in response to NMDA receptor activation. By contrast, dual-pass CRD-NRG1 and NRG3 are constitutively processed by BACE and accumulate on axons where they interact with ErbB4 in juxtacrine mode. These findings reveal a previously unknown functional relationship between membrane topology, protein processing, and subcellular distribution, and suggest that single- and dual-pass NRGs regulate neuronal functions in fundamentally different ways.

Neuregulin1 alpha activates migration of neuronal progenitors expressing ErbB4

Deficits in neuronal migration during development in the central nervous system may contribute to psychiatric diseases. The ligand neuregulin1 (NRG1) and its receptor ErbB4 are genes conferring susceptibility to schizophrenia, playing a key role in the control of neuronal migration both during development and adulthood. Several NRG1 and ErbB4 isoforms were identified, which deeply differ in their characteristics. Here we focused on the four ErbB4 isoforms and the two NRG1 isoforms differing in their EGF-like domain, namely α and β. We hypothesized that these isoforms, which are differently regulated in schizophrenic patients, could play different roles in neuronal migration. Our hypothesis was strengthened by the observation that both NRG1α and NRG1β and the four ErbB4 isoforms are expressed in the medial and lateral ganglionic eminences and in the cortex during development in rat. We analysed in vitro the signal transduction pathways activated by the different ErbB4 isoforms following the treatment with soluble recombinant NRG1α or NRG1β and the ability to stimulate migration. Our data show that two ErbB4 isoforms, namely JMa-cyt2 and JMb-cyt1, following NRG1α and NRG1β treatment, strongly activate AKT phosphorylation, conferring high migratory activity to neuronal progenitors, thus demonstrating that both NRG1α and NRG1β can play a role in neuronal migration.

Targeted disruption of Nrg1 in granulosa cells alters the temporal progression of oocyte maturation

Neuregulin 1 (NRG1) is induced in granulosa cells by LH and acts on granulosa and cumulus cells during ovulation. In this study, we sought to determine the role of NRG1 in oocyte maturation by generating a granulosa cell-specific Nrg1 knockout mouse (Nrg1(flox/flox);Cyp19a1Cre mice [gcNrg1KO]). In the gcNrg1KO mice, meiosis was induced 2 hours earlier than in control mice. More than 60% of the oocytes in the mutant mice spontaneously re-resumed meiosis beyond the MII stage. The percentage of successful fertilization was comparable in oocytes of both genotypes collected at 14 or 16 hours after human chorionic gonadotropin injection but was significantly lower in oocytes of the gcNrg1KO mice at 18 or 20 hours. The number of pups per litter was significantly decreased in gcNrg1KO mice. To determine the molecular events associated with the abnormal progression of meiosis in the gcNrg1KO mouse oocytes, the defects of cumulus/granulosa cell functions were analyzed. The expression of genes involved in luteinization and cumulus expansion was significantly higher at 2 hours after human chorionic gonadotropin injection in the gcNrg1KO mice; this was related to abnormal activation of protein kinase C (PKC) and phosphorylation of connexin-43 in cumulus cells. Changes in connexin-43 by PKC might lead to early meiotic resumption of oocytes in gcNrg1KO mice. We conclude that NRG1 is induced by LH in mural granulosa cells and exerts an important regulatory role in oocyte meiotic maturation and competence by reducing PKC activation in cumulus cells and preventing premature progression to the MII stage that leads to abnormal fertilization and fertility.

The ERBB network: at last, cancer therapy meets systems biology

Although it is broadly agreed that the improved treatment of patients with cancer will depend on a deeper molecular understanding of the underlying pathogenesis, only a few examples are already available. This Timeline article focuses on the ERBB (also known as HER) network of receptor tyrosine kinases (RTKs), which exemplifies how a constant dialogue between basic research and medical oncology can translate into both a sustained pipeline of novel drugs and ways to overcome acquired treatment resistance in patients. We track the key early discoveries that linked this RTK family to oncogenesis, the course of pioneering clinical research and their merger into a systems-biology framework that is likely to inspire further generations of effective therapeutic strategies.

Neuregulin promotes incomplete autophagy of prostate cancer cells that is independent of mTOR pathway inhibition

Background

Growth factors activating the ErbB receptors have been described in prostate tumors. The androgen dependent prostate cancer cell line, LNCaP, expresses the ErbB-1, ErbB-2 and ErbB-3 receptor tyrosine kinases. Previously, it was demonstrated that NRG activates ErbB-2/ErbB-3 heterodimers to induce LNCaP cell death, whereas, EGF activates ErbB-1/ErbB-1 or ErbB-1/ErbB-2 dimers to induce cell growth and survival. It was also demonstrated that PI3K inhibitors repressed this cell death suggesting that in androgen deprived LNCaP cells, NRG activates a PI3K-dependent pathway associated with cell death.

Methodology/Principal Findings

In the present study we demonstrate that NRG induces autophagy in LNCaP cells, using LC3 as a marker. However, the autophagy induced by NRG may be incomplete since p62 levels elevate. We also demonstrated that NRG- induced autophagy is independent of mammalian target of rapamycin (mTOR) inhibition since NRG induces Akt and S6K activation. Interestingly, inhibition of reactive oxygen species (ROS) by N-acetylcysteine (NAC), inhibited NRG-induced autophagy and cell death. Our study also identified JNK and Beclin 1 as important components in NRG-induced autophagy and cell death. NRG induced elevation in JNK phosphorylation that was inhibited by NAC. Moreover, inhibitor of JNK inhibited NRG-induced autophagy and cell death. Also, in cells overexpressing Bcl-2 or cells expressing sh-RNA against Beclin 1, the effects of NRG, namely induction of autophagy and cell death, were inhibited.

Conclusions/Significance

Thus, in LNCaP cells, NRG-induces incomplete autophagy and cell death that depend on ROS levels. These effects of NRG are mediated by signaling pathway that activates JNK and Beclin 1, but is independent of mTOR inhibition.

Comprehensive analysis of NRG1 common and rare variants in Hirschsprung patients

Hirschsprung disease (HSCR, OMIM 142623) is a developmental disorder characterized by the absence of ganglion cells along variable lengths of the distal gastrointestinal tract, which results in tonic contraction of the aganglionic gut segment and functional intestinal obstruction. The RET proto-oncogene is the major gene for HSCR with differential contributions of its rare and common, coding and noncoding mutations to the multifactorial nature of this pathology. Many other genes have been described to be associated with the pathology, as NRG1 gene (8p12), encoding neuregulin 1, which is implicated in the development of the enteric nervous system (ENS), and seems to contribute by both common and rare variants. Here we present the results of a comprehensive analysis of the NRG1 gene in the context of the disease in a series of 207 Spanish HSCR patients, by both mutational screening of its coding sequence and evaluation of 3 common tag SNPs as low penetrance susceptibility factors, finding some potentially damaging variants which we have functionally characterized. All of them were found to be associated with a significant reduction of the normal NRG1 protein levels. The fact that those mutations analyzed alter NRG1 protein would suggest that they would be related with HSCR disease not only in Chinese but also in a Caucasian population, which reinforces the implication of NRG1 gene in this pathology.

Mutations in the NRG1 gene are associated with Hirschsprung disease

Hirschsprung disease (HSCR, congenital colon aganglionosis) is a relatively common complex genetic condition caused by abnormal development of the enteric nervous system (ENS). Through a recent genome-wide association study conducted on Chinese HSCR patients, we identified a new HSCR contributing locus, neuregulin 1 (NRG1; 8p12), a gene known to be involved in the development of the ENS. As genes in which disease-associated common variants are found are to be considered as candidates for the search of deleterious rare variants (RVs) in the coding sequences, we sequenced the NRG1 exons of 358 sporadic HSCR patients and 333 controls. We identified a total of 13 different heterozygous RVs including 8 non-synonymous (A28G, E134K, V266L, H347Y, P356L, V486M, A511T, P608A) and 3 synonymous amino acid substitutions (P24P, T169T, L483L), a frameshift (E239fsX10), and a c.503-4insT insertion. Functional analysis of the most conserved non-synonymous substitutions, H347Y and P356L, showed uneven intracellular distribution and aberrant expression of the mutant proteins. Except for T169T and V486M, all variants were exclusive to HSCR patients. Overall, there was a statistically significant over-representation of NRG1 RVs in HSCR patients (p = 0.008). We show here that not only common, but also rare variants of the NRG1 gene contribute to HSCR. This strengthens the role of NRG1.

Reciprocal signalling between NR2 subunits of the NMDA receptor and neuregulin1 and their role in schizophrenia

Schizophrenia is a debilitating neurodevelopmental psychiatric disorder. Both the N-methyl-D-aspartate receptor (NMDAR) and neuregulin1 (NRG1) are key molecules involved in normal brain development that have been linked to schizophrenia pathology and aetiology. The NR2 proteins are critical structural and functional subunits of the NMDAR and are developmentally and spatially regulated. Altered NR2 gene and protein expression has been found in human post-mortem schizophrenia brain tissue together with changes in NRG1 and its receptor ErbB4. The NR2 subunits and ErbB4 share a common anchoring domain on the postsynaptic density and therefore a disruption to either of these molecules may influence the functioning of the other. It has been shown that NRG1 signalling can affect NMDAR levels and function, particularly phosphorylation of the NR2 subunits. However little is known about the possible effects of NMDAR dysfunction on NRG1 signalling, which is important with regards to schizophrenia aetiology as numerous risk factors for the disorder can alter NMDAR functioning during early brain development. This review focuses on the role of the NMDA receptor subunits and NRG1 signalling in schizophrenia and proposes a mechanism by which a disruption to the NMDAR, particularly via altering the balance of NR2 subunits during early development, could influence NRG1 signalling.

Secretion of EGF-like domain of heregulinβ promotes axonal growth and functional recovery of injured sciatic nerve

Neuregulin 1 (NRG1) and epidermal growth factor receptor (ErbB) signaling pathways control Schwann cells during axonal regeneration in an injured peripheral nervous system. We investigated whether a persistent supply of recombinant NRG1 to the injury site could improve axonal growth and recovery of sensory and motor functions in rats during nerve regeneration. We generated a recombinant adenovirus expressing a secreted form of EGF-like domain from Heregulinβ (sHRGβE-Ad). This virus, sHRGβE-Ad allowed for the secretion of 30-50 ng of small sHRGβE peptides per 10(7-8) virus particle outside cells and was able to phosphorylate ErbB receptors. Transduction of the concentrated sHRGβE-Ad into an axotomy model of sciatic nerve damage caused an effective promotion of nerve regeneration, as shown by histological features of the axons and Schwann cells, as well as increased expression of neurofilaments, GAP43 and S100 in the distal stump of the injury site. This result is consistent with longer axon lengths and thicker calibers observed in the sHRGβE-Ad treated animals. Furthermore, sensory and motor functions were significantly improved in sHRGβE-Ad treated animals when evaluated by a behavioral test. These results suggest a therapeutic potential for sHRGβE-Ad in treatment of peripheral nerve injury.

Neuregulin-ErbB signaling promotes microglial proliferation and chemotaxis contributing to microgliosis and pain after peripheral nerve injury

A key component in the response of the nervous system to injury is the proliferation and switch to a "proinflammatory" phenotype by microglia (microgliosis). In situations where the blood-brain barrier is intact, microglial numbers increase via the proliferation and chemotaxis of resident microglia; however, there is limited knowledge regarding the factors mediating this response. After peripheral nerve injury, a dorsal horn microgliosis develops, which directly contributes to the development of neuropathic pain. Neuregulin-1 (NRG-1) is a growth and differentiation factor with a well characterized role in neural and cardiac development. Microglia express the NRG1 receptors erbB2, 3, and 4, and NRG1 signaling via the erbB2 receptor stimulated microglial proliferation, chemotaxis, and survival, as well as interleukin-1beta release in vitro. Intrathecal treatment with NRG1 resulted in microglial proliferation within the dorsal horn, and these cells developed an activated morphology. This microglial response was associated with the development of both mechanical and cold pain-related hypersensitivity. Primary afferents express NRG1, and after spinal nerve ligation (SNL) we observed both an increase in NRG1 within the dorsal horn as well as activation of erbB2 specifically within microglia. Blockade of the erbB2 receptor or sequestration of endogenous NRG after SNL reduced the proliferation, the number of microglia with an activated morphology, and the expression of phospho-P38 by microglia. Furthermore, consequent to such changes, the mechanical pain-related hypersensitivity and cold allodynia were reduced. NRG1-erbB signaling therefore represents a novel pathway regulating the injury response of microglia.

Genome-wide association study identifies NRG1 as a susceptibility locus for Hirschsprung's disease

Hirschsprung's disease (HSCR), or aganglionic megacolon, is a congenital disorder characterized by the absence of enteric ganglia in variable portions of the distal intestine. RET is a well-established susceptibility locus, although existing evidence strongly suggests additional loci contributing to sporadic HSCR. To identify these additional genetic loci, we carried out a genome-wide association study using the Affymetrix 500K marker set. We successfully genotyped 293,836 SNPs in 181 Chinese subjects with sporadic HSCR and 346 ethnically matched control subjects. The SNPs most associated with HSCR were genotyped in an independent set of 190 HSCR and 510 control subjects. Aside from SNPs in RET, the strongest overall associations in plausible candidate genes were found for 2 SNPs located in intron 1 of the neuregulin1 gene (NRG1) on 8p12, with rs16879552 and rs7835688 yielding odds ratios of 1.68 [CI(95%):(1.40, 2.00), P = 1.80 x 10(-8)] and 1.98 [CI(95%):(1.59, 2.47), P = 1.12 x 10(-9)], respectively, for the heterozygous risk genotypes under an additive model. There was also a significant interaction between RET and NRG1 (P = 0.0095), increasing the odds ratio 2.3-fold to 19.53 for the RET rs2435357 risk genotype (TT) in the presence of the NRG1 rs7835688 heterozygote, indicating that NRG1 is a modifier of HSRC penetrance. Our highly significant association findings are backed-up by the important role of NRG1 as regulator of the development of the enteric ganglia precursors. The identification of NRG1 as an additional HSCR susceptibility locus not only opens unique fields of investigation into the mechanisms underlying the HSCR pathology, but also the mechanisms by which a discrete number of loci interact with each other to cause disease.

Neuregulin-1 haplotype HAP(ICE) is associated with lower hippocampal volumes in schizophrenic patients and in non-affected family members

The neuregulin-1 (NRG1) gene on chromosome 8p has been suggested as a potential susceptibility gene for schizophrenia. The exact way in which genetic variation in NRG1 might impact on this susceptibility for the disorder is a focus of current research. The present study aimed at investigating the possible relationship between a putative NRG1 at-risk haplotype (HAP(ICE)) and hippocampal volumes in schizophrenic patients and their healthy first-degree relatives. We genotyped 30 schizophrenic patients and 52 non-affected family members with regard to the presence or absence of the NRG1 haplotype HAP(ICE). Structural magnetic resonance imaging was used to determine hippocampal brain volumes in the same subjects. Patients and relatives carrying haplotype HAP(ICE) both had smaller relative hippocampal volumes as compared to patients or relatives who did not carry this haplotype. These findings provide first direct evidence for a link between NRG1 genetic variation and hippocampal volume reductions in schizophrenic patients and non-affected relatives. This preliminary evidence may help to guide further research into the pathophysiological pathways that underlie this genetic susceptibility for schizophrenia.

The role of Neuregulin-1beta/ErbB signaling in the heart

Products of the Neuregulin-1 (Nrg-1) gene, along with the ErbB family of receptor tyrosine kinases through which Nrg-1 ligands signal, play a critical role during cardiovascular development. Through studies of genetically manipulated mice, as well as studies in cells isolated from adult hearts, it appears that Nrg-1/ErbB signaling is an essential paracrine mediator of cell-cell interactions that not only regulates tissue organization during development, but also helps to maintain cardiac function throughout an organism's life. Studies in cells isolated from the heart demonstrate that Nrg-1 can activate a number of signaling pathways, which mediate cellular adaptations to stress in the myocardium. These observations provide insight as to why ErbB2-targeted cancer treatments have deleterious effects on cardiac function in some cancer patients. Moreover emerging data suggest that Nrg-1 ligands might be useful clinically to restore cardiac function after cardiac injury. In this review we will attempt to synthesize the literature behind this rapidly growing and exciting area of research.

Promotion of spermatogonial proliferation by neuregulin 1 in newt (Cynops pyrrhogaster) testis

We have previously shown that mammalian follicle-stimulating hormone (FSH) promotes the proliferation of spermatogonia and their differentiation into primary spermatocytes in organ culture of newt testis. In the current study, we performed microarray analysis to isolate local factors secreted from somatic cells upon FSH treatment and acting on the germ cells. We identified neuregulin 1 (NRG1) as a novel FSH-upregulated clone homologous to mouse NRG1 known to control cell proliferation, differentiation and survival in various tissues. We further isolated cDNAs encoding two different clones. Amino acid sequences of the two clones were 75% and 94% identical to Xenopus leavis immunoglobulin (Ig)-type and cysteine-rich domain (CRD)-type NRG1, respectively, which had distinct sequences in their N-terminal region but identical in their epidermal growth factor (EGF)-like domain. Semi-quantitative and quantitative PCR analyses indicated that both clones were highly expressed at spermatogonial stage than at spermatocyte stage. In vitro FSH treatment increased newt Ig-NRG1 (nIg-NRG1) mRNA expression markedly in somatic cells, whereas newt CRD-NRG1 (nCRD-NRG1) mRNA was only slightly increased by FSH. To elucidate the function of newt NRG1 (nNRG1) in spermatogenesis, recombinant EGF domain of nNRG1 (nNRG1-EGF) was added to organ and reaggregated cultures with or without somatic cells: it promoted spermatogonial proliferation in all cases. Treatment of the cultures with the antibody against nNRG1-EGF caused remarkable suppression of spermatogonial proliferation activated by FSH. These results indicated that nNRG1 plays a pivotal role in promoting spermatogonial proliferation by both direct effect on spermatogonia and indirect effect via somatic cells in newt testes.

Elevated neuregulin-1 and ErbB4 protein in the prefrontal cortex of schizophrenic patients

Neuregulin-1 (NRG1) and its receptor, ErbB4, have been implicated in schizophrenia at both gene and transcript levels. The present investigation compared NRG1 and ErbB4 protein levels in prefrontal cortical (PFC) cytoplasmic and nuclear fractions among normal, schizophrenic, bipolar and major depressed subjects from the Stanley Consortium. We used immunoblotting procedures to examine potential NRG1 and ErbB4 immunoreactive bands, but specifically quantified NRG1 immunoreactive signals at 42, 48 and 53 kDa and ErbB4 immunoreactive signals at 21, 55, 60 and 180 kDa. PFC cytoplasmic 53 kDa NRG1 protein levels were significantly increased (approximately 20%) in schizophrenic patients relative to each of the other subject groups. We also detected diagnostic effects on PFC cytoplasmic full-length (180 kDa) ErbB4 protein levels, and post hoc tests revealed that these quantities were significantly increased (approximately 30%) in schizophrenic patients relative to normal and to depressed subjects. In addition, we examined the levels of potential ErbB4 cleavage products at 21, 55 and 60 kDa relative to those of full-length ErbB4 in the PFC fractions. We detected trends for diagnostic effects on PFC cytoplasmic 21 kDa/180 kDa and 55 kDa/180 kDa ratios, and post hoc tests revealed that these ratios were significantly reduced in schizophrenic patients relative to normal individuals. Our investigation suggests that schizophrenia-associated NRG1 and ErbB4 mRNA elevations also occur at the protein level and may be specific to schizophrenia. We hypothesize that ErbB4 proteolytic processing may also be altered in schizophrenia, yielding altered ratios of functionally distinct forms of ErbB4.

Growth factors in the treatment of degenerative retinal disorders

There are currently a number of degenerative conditions, both inherited and acquired, that affect the retina and lead to blindness. Retinal photoreceptors degenerate from inherited conditions, such as retinitis pigmentosa or as a result of light damage or normal ageing; retinal ganglion cells degenerate from optic nerve injury or glaucoma. Current research in this field includes the use of growth factors to: (1) inhibit the degenerative processes; (2) promote regeneration of the retina from the pigmented epithelium; and (3) improve the conditions for transplantation of new cells to the retina by expanding the photoreceptor cell populations in vitro. The results to date have shown that a number of different growth factors promote survival of retinal cells in vitro and in vivo. In addition, some of the same factors can stimulate regeneration in the developing retina and act as mitogens for the retinal progenitor cells. It is likely that a combination of these approaches will ultimately be important for the treatment of the various retinal degenerations.

Immunohistochemical Evidence for Impaired Neuregulin-1 Signaling in the Prefrontal Cortex in Schizophrenia and in Unipolar Depression

In the central nervous system (CNS), neuregulin-1 (NRG-1) proteins function in neuronal migration, differentiation, and survival of oligodendrocytes. The NRG-1 gene codes for at least 15 different isoforms, which may be classified on the basis of their molecular structure. At least two different haplotypes of the NRG-1 gene may be associated with schizophrenia. An abnormal expression pattern of NRG-1 mRNA was found in the prefrontal cortex of schizophrenic patients in comparison to controls. We here show that the NRG-1alpha isoform is significantly reduced in white matter of the prefrontal cortex in schizophrenia but not in affective disorder. In the prefrontal gray matter, the density of NRG-1alpha expressing neurons was reduced in individuals with schizophrenia and in unipolar patients. We studied brains of 22 schizophrenics, 12 patients with affective disorders (7 unipolar and 5 bipolar), and 22 matched controls. NRG-1alpha immunoreactive material was detected with a polyclonal antiserum against the synthetic peptide from alpha-type EGF-like domain of human NRG. The demonstrated decreased number of NRG-1 immunoreactive neurons in the brains of schizophrenics and patients with unipolar depression points to an important role of this NRG-1alpha splice variant in neuropsychiatric disorders. Reduced NRG-1alpha protein concentrations were found in brains of schizophrenics after Western blot analysis. The diminished expression of NRG-1alpha strongly supports an early neurodevelopmental component to schizophrenia.

Neuregulin 1 growth factors regulate proliferation but not apoptosis of a CNS neuronal progenitor cell line

Growth factor-dependent proliferation of neuronal progenitors is an essential stage in CNS development. Although several of these growth factors have been identified, high levels of neuregulin 1 (NRG1) mRNA and protein expression in the CNS during the time of neuronal progenitor expansion suggest NRG1 growth factors may also play a key role in their proliferation. No previous studies have examined the expression of multiple NRG1 isoforms and receptors in these progenitors and their role in proliferation or apoptosis. Using a rat CNS clonal cell line with neuronal progenitor properties, we show for the first time these cells coexpress multiple NRG1 isoforms (NRGbeta1, NRGbeta3, CRD-NRGbeta, and SMDF, but not GGF2 or any alpha isoforms) and all three cognate receptors (erbB2-4). We also show for the first time the presence of mRNA for all four variants of the erbB4 receptor in a single CNS cell type. Neutralizing antibody treatments suggest NRG1 isoforms and receptors are involved in proliferation but not apoptosis of these cells. This model system should be useful in future studies of the ligand specificity and function(s) of the erbB4 receptor variants.

Specification of optic nerve oligodendrocyte precursors by retinal ganglion cell axons

Cell fate commitment in the developing CNS frequently depends on localized cell-cell interactions. In the avian visual system the optic nerve oligodendrocytes are derived from founder cells located at the floor of the third ventricle. Here we show that the induction of these founder cells is directly dependent on signaling from the retinal ganglion cell (RGC) axons. The appearance of oligodendrocyte precursor cells (OPCs) correlates with the projection of RGC axons, and early eye removal dramatically reduces the number of OPCs. In vitro signaling from retinal neurites induces OPCs in responsive tissue. Retinal axon induction of OPCs is dependent on sonic hedgehog (Shh) and neuregulin signaling, and the inhibition of either signal reduces OPC induction in vivo and in vitro. The dependence of OPCs on retinal axonal cues appears to be a common phenomenon, because ocular retardation (or(J)) mice lacking optic nerve have dramatically reduced OPCs in the midline of the third ventricle.

Ras inhibition results in growth arrest and death of androgen-dependent and androgen-independent prostate cancer cells

Prostate cancer is one of the most frequently diagnosed cancers in human males. Progression of these tumors is facilitated by autocrine/paracrine growth factors which activate critical signaling cascades that promote prostate cancer cell growth, survival and migration. Among these, Ras pathways have a major role. Here we examined the effect of the Ras inhibitor S-trans, trans-farnesylthiosalicylic acid (FTS), on growth and viability of androgen-dependent and androgen-independent prostate cancer cells. FTS downregulated Ras, inhibited signaling to Akt and reduced the levels of cell-cycle regulatory proteins including cyclin D1, p-RB, E2F-1 and cdc42 in LNCaP and PC3 cells. Consequently the anchorage-dependent and anchorage-independent growth of LNCaP and PC3 cells were inhibited. FTS also induced apoptotic cell death which was inhibited by the broad-spectrum caspases inhibitor, Boc-asp-FMK. Our study demonstrated that androgen-dependent and androgen-independent prostate cancer cells require active Ras for growth and survival. Ras inhibition by FTS results in growth arrest and cell death. FTS may be qualified as a potential agent for the treatment of prostate cancer.

Localization of neuregulin-1α (heregulin-α) and one of its receptors, ErbB-4 tyrosine kinase, in developing and adult human brain

Using immunohistochemistry, Western blot analysis, and RT-polymerase chain reaction, we studied the distribution of neuregulin-1 splice variant alpha (NRG-1alpha) and one of its putative receptors, ErbB-4 tyrosine kinase, in human brain. In the pre- and perinatal human brain immunoreactivity was confined to numerous neurons, with the highest cell density found in cortical gray matter, hypothalamus and cerebellum. In the adult brain, single cortical gray and white matter neurons showed NRG-1alpha immunoreactivity. Occasionally, immunoreactive oligodendrocytes were observed. NRG-1alpha-expressing neurons were also found in the hypothalamus, hippocampus, basal ganglia and brain stem. Application of two antibodies recognizing alpha and beta isoforms revealed a different distribution pattern in that many cortical and hippocampal pyramidal neurons were labeled. ErbB-4 immunoreactivity was expressed in both neurons and oligodendrocytes. Our data show that NRG-1alpha expression is lower in the adult human brain than in the developing brain, and, therefore, support a role for NRG-1alpha in brain development.

Differential expression of neuregulins and their receptors in the olfactory bulb layers of the developing mouse

Neuregulins (NRGs), and their cognate receptors (ErbBs), play essential roles in numerous aspects of neural development and adult synaptic plasticity. The goal of this study was to investigate the developmental expression profiles of these molecules during the olfactory bulb (OB) maturation. The OB is a highly organized structure with cell types and synaptic connections segregated into discrete anatomical layers. We employed a novel approach by combining single-layer microdissection at different development ages, with isoform-specific semi-quantitative RT-PCR and Western blotting to monitor layer-specific developmental profiles of these molecules and alternate splice variants. Layer and age specific regulation was observed for the ErbB4 splice variants JMa/JMb and NRG-1-beta1/beta2 forms. With the exception of the outermost (nerve) layer, ErbB4-JMb and NRG-1-beta1 are expressed throughout the OB and their expressions decrease in the adult age in most layers. In contrast both ErbB4-JMa and NRG-1-beta2 are highly expressed in the granule cell layer in the early postnatal OB. This early postnatal expression correlates with the dramatic change from radial glia to astrocytes and appearance of the bulk of granule cells occurring at this developmental stage.

Expression and differential signaling of heregulins in pancreatic cancer cells

The EGF family of ligands and receptors plays an important role in the pathogenesis of pancreatic ductal adenocarcinoma (PDAC) and contributes to its aggressiveness. A number of molecular approaches have been developed to block these pathways, and studies have already proven the clinical benefit of this concept in PDAC. In the present study, we sought to determine the potential role of heregulins (HRGs), a family of EGF-like growth factors, in PDAC. Quantitative RT-PCR analysis revealed that HRGs as well as its signaling ErbB receptors were present in 4 of 4 human pancreatic cancer cell lines (PCCL). HRG-beta1 stimulated the growth of 3 of 4 PCCL, whereas HRG-alpha1 inhibited cell growth in 3 of 4 cell lines. Responses towards HRGs could in part be predicted by ErbB2 and ErbB3 expression levels. HRGs induced phosphorylation of different ErbB receptors as well as activation of MAPK, p38MAPK, JNK and PI3K in a cell- and ligand-specific manner. In vivo, HRG was upregulated in pancreatic cancer tissues and localized predominantly in the cancer cells. High HRG-beta levels but not HRG-alpha levels were associated with decreased patient survival. In conclusion, HRG is expressed by pancreatic cancer cells and influences pancreatic cancer cell growth and patient survival.

Heregulin induces glial cell line-derived neurotrophic growth factor-independent, non-branching growth and differentiation of ureteric bud epithelia

We have purified a protein present in a conditioned medium derived from the metanephric mesenchyme that supports non-branching growth and epithelial differentiation of the isolated ureteric bud (UB) independent of glial cell line-derived neurotrophic growth factor (GDNF). By sequential liquid chromatography, together with protein microsequencing, the protein was identified as heregulin (HRG)alpha. The addition of recombinant HRG to the isolated UB grown in three-dimensional culture confirmed the proliferative activity of HRG. In branching UBs induced by whole metanephric mesenchyme cell-conditioned medium, proliferating cells were localized at ampullae, where a binding receptor for GDNF, GFRalpha1, was found. In HRG-induced UBs, however, the expression of GFRalpha1 was down-regulated, and proliferating cells were distributed throughout the structure. Electron microscopic examination of the HRG-induced UB revealed the presence of structurally mature and polarized epithelial cells reminiscent of the epithelial cells found in the stalk portion of the branching UB. cDNA array analysis further revealed that genes ontologically classified as developmental were down-regulated by HRG, whereas those involved in transport were up-regulated. For example, the mRNA for the GDNF receptors, GFRalpha1 and ret9, was down-regulated, whereas the mRNA for collecting duct transporters, such as urea transporter2, aquaporin3, and sodium-hydrogen exchanger2 was up-regulated in HRG-treated UBs compared with UBs grown in the presence of branch-promoting factors. Moreover, HRG promoted growth of UBs cultured in the absence of GDNF. Taken together, the data suggest that HRG supports UB epithelial cell differentiation and non-GDNF-dependent growth, raising the possibility that this kind of activity plays a role in the growth and differentiation of the stalk portion of the branching epithelial UB.

Neuregulin-1 enhances survival of human astrocytic glioma cells

Malignant astrocytic gliomas, referred to as astrocytomas, represent the most commonly diagnosed adult primary brain tumor. These tumors are characterized by unrelenting growth that is often resistant to chemotherapy and radiation therapy. Tumor expansion into the healthy surrounding brain tissue produces severe and often fatal consequences. In this study, we examine the potential for the neuregulin-1/erbB receptor signaling cascade to contribute to this process by modulating glioma cell growth. Using antibodies specific for the erbB receptors, we demonstrate the expression patterns for the erbB2, erbB3, and erbB4 receptors in human glioma biopsy samples. We then verify receptor expression in a panel of human glioma cell lines. Next, we investigate the status of the erbB2 and erbB3 receptors in the human glioma cell lines and find that they are constitutively tyrosine-phosphorylated and heterodimerized. Subsequently, we demonstrate that theses same cell lines express membrane bound and released forms of neuregulins, the erbB receptor ligands, suggesting a possible autocrine or paracrine signaling network. Furthermore, we show that exogenous activation of erbB2 and erbB3 receptors in U251 glioma cells by recombinant Nrg-1beta results in enhanced glioma cell growth under conditions of serum-deprivation. This enhancement is due to an increase in cell survival rather than an increase in cell proliferation and is dependent on the activation of erbB2 and phosphatidylinositol-3 kinase (PI3K). Moreover, Nrg-1beta activates an inhibitor of apoptosis, Akt, implying a possible role for this kinase in mediating Nrg-1beta effects in gliomas. This data suggests that glioma cells may use autocrine or paracrine neuregulin-1/erbB receptor signaling to enhance cell survival under conditions where growth would otherwise be limited.

Roles for neuregulins in human cancer

The human epidermal growth factor (EGF) receptor (HER) family of receptor tyrosine kinases has frequently been implicated in cancer. Apart from overexpression or mutation of these receptors, also the aberrant autocrine or paracrine activation of HERs by EGF-like ligands may be important in cancer progression. Neuregulins constitute a family of EGF-like ligands that bind to HER3 or HER4, preferably forming heterodimers with the orphan receptor HER2. Mesenchymal neuregulin typically serves as a pro-survival and pro-differentiation signal for adjacent epithelia. Disruption of the balance between proliferation and differentiation, because of autocrine production by the epithelial cells, increased sensitivity to paracrine signals or disruption of the spatial organization, may lead to constitutive receptor activation, in the absence of receptor overexpression. Consequently, the analysis of ligand expression and/or activated receptors in tumor samples may broaden the group of patients that can benefit from targeted therapies.

Neuregulin-1beta induces neurite extension and arborization in cultured hippocampal neurons

Neuregulin-1 (NRG-1) growth and differentiation factors and their erbB receptors are hypothesized to promote embryonic hippocampal neuron differentiation via as yet unknown mechanisms. We have found that NRG-1beta increases the outgrowth of primary neurites, neuronal area, total neurite length, and neuritic branching in E18 hippocampal neurons. NRG-1beta effects on neurite extension and arborization are similar to, but not additive with, those of brain-derived neurotrophic factor and reflect direct NRG-1 action on hippocampal neurons as these cells express the NRG-1 receptors erbB2 and erbB4, the erbB-specific inhibitor PD158780 decreases NRG-1beta induced neurite outgrowth, and NRG-1beta stimulation induces p42/44 ERK phosphorylation. Pharmacological inhibition of p42/44 ERK and protein kinase C (PKC), but not PI3K or p38 MAP kinase, inhibits NRG-1beta-induced neurite extension and elaboration. We conclude that NRG-1beta stimulates hippocampal neurite extension and arborization via a signaling pathway that involves erbB membrane tyrosine kinases (erbB2 and/or erbB4), p42/44 ERK, and PKC.

Neuregulin-1 induces branching morphogenesis in the developing lung through a P13K signal pathway

Neuregulin-1 (NRG-1) induces signal transduction through the activation of its receptor, a heterodimer of human epidermal growth factor receptors 2 and 3 (HER2/HER3). Signal transduction through this receptor/ligand system plays a critical role in the developing heart, mammary gland, and nervous systems. Previous studies showed that NRG-1-induced HER2 activation resulted in pulmonary epithelial cell proliferation in the human fetal lung. The authors hypothesized that NRG-1 further contributes to lung development and maturation by inducing branching morphogenesis. In the present study, the authors show that NRG-1, HER2, and HER3, but not HER4, are expressed in the developing mouse lung. Addition of NRG-1 to fetal lung explants increased lung branching morphogenesis by 32% (P < .05). This increase in branching was blocked by 2C4, an antibody directed against HER2 that inhibits its dimerization and subsequent NRG-1-induced signal transduction. To gain an understanding of the intracellular signaling pathways involved in NRG-1-induced branching morphogenesis, the authors specifically blocked the phosphatidylinositol-3 kinase (PI3K) and mitogen activation protein kinase (MAPK) pathways. Inhibition of PI3K signaling significantly decreased NRG-1-induced branching morphogenesis (P < .05). Inhibition of NRG-1-induced MAPK activation had no effect on explant branching morphogenesis. These data suggest that NRG-1, binding to the HER2/HER3 heterodimer receptor complex, induces pulmonary branching morphogenesis through HER2 activation of the PI3K pathway.

Neurotrophic and neuroprotective effects of the neuregulin glial growth factor-2 on dopaminergic neurons in rat primary midbrain cultures

Glial growth factor-2 (GGF2) and other neuregulin (NRG) isoforms have been shown to play important roles in survival, migration, and differentiation of certain neural and non-neural cells. Because midbrain dopamine (DA) cells express the NRG receptor, ErbB4, the present study examined the potential neurotrophic and/or neuroprotective effects of GGF2 on cultured primary dopaminergic neurons. Embryonic day 14 rat mesencephalic cell cultures were maintained in serum-free medium and treated with GGF2 or vehicle. The number of tyrosine hydroxylase-positive (TH+) neurons and high-affinity [3H]DA uptake were assessed at day in vitro (DIV) 9. Separate midbrain cultures were treated with 100 ng/mL GGF2 on DIV 0 and exposed to the catecholamine-specific neurotoxin 6-hydroxydopamine (6-OHDA) on DIV 4. GGF2 treatment significantly increased DA uptake, the number of TH+ neurons, and neurite outgrowth when compared to the controls in both the serum-free and the 6-OHDA-challenged cultures. Furthermore, three NRG receptors were detected in the midbrain cultures by western blot analysis. Immunostaining for glial fibrillary acidic protein revealed that GGF2 also weakly promoted mesencephalic glial proliferation in the midbrain cultures. These results indicate that GGF2 is neurotrophic and neuroprotective for developing dopaminergic neurons and suggest a role for NRGs in repair of the damaged nigrostriatal system that occurs in Parkinson's disease.

The therapeutic potential of stem cells in the treatment of craniofacial abnormalities

Anomalies associated with the vertebrate head and face account for a third of all reported major birth defects. Of the principle cell populations that participate in formation of the craniofacial complex, the neural crest is central, generating much of the peripheral nervous system and constituting the predominant connective tissue-forming mesenchyme of the facial skeleton. Many craniofacial anomalies are, therefore, largely attributed to defects in neural crest cell development. Neural crest cells exhibit many of the features of stem cells; they are multipotent, remarkably plastic and have a limited capacity for self-renewal. This article will review recent studies that demonstrate the ability of stem cells to generate neural crest cell populations that form appropriate neural crest derivatives in the developing craniofacial complex, and will discuss the potential application for stem cells in the treatment of craniofacial disorders.

Neuregulin induces proliferation of neural progenitor cells via PLC/PKC pathway

Nestin-expressing neural progenitor cells (NPCs) have been isolated from hippocampus of brains and propagated with epidermal growth factor and basic fibroblast growth factor (bFGF). However, the underlying signaling mechanisms regulating NPC proliferation remain elusive. Here we showed that neuregulinbeta1 (NRG), like bFGF, effectively promoted the proliferation of hippocampus-derived NPCs and maintained the progenitor states of NPCs. Activation of protein kinase C (PKC), a downstream effector of phospholipase C (PLC), with 12-O-tetradecanoylphorbol-13-acetate (TPA) mimicked the NRG-induced proliferation of NPCs. The synergic effect of TPA plus NRG on neurosphere growth further prompted us to find that NRG induced NPC propagation through PLC/PKC signaling pathway. ErbB4, an important functional receptor of NRG, had an interaction with PLCgamma1 protein. In addition, inactivation of PLC pathway led to severe proliferative suppression of NPCs. Our study suggests that activation of PLC/PKC pathway plays an essential role in the NRG-induced proliferation of hippocampus-derived NPCs.

Neuregulin 1 and schizophrenia

We discuss in this review the role of the neuregulin (NRG1) gene in schizophrenia. NRG1 contributes to the genetics of schizophrenia in both Icelandic and Scottish schizophrenia patients. NRG1 participates in glutamatergic signaling by regulating the N-methyl-D-aspartate (NMDA) receptor through the interaction of the NRG1 protein and its receptors. NRG1 plays a central role in neural development and is most likely involved in regulating synaptic plasticity, or how the brain responds or adapts to the environment. The discovery that defects in NRG1 signaling may be involved in some cases of schizophrenia, not only implicates NRG1, but suggests that its biological pathway, active both at developing and mature synapses, is worth inspecting further in a search for other schizophrenia genes possibly in epistasis with NRG1.

Olfactory ensheathing cells (OECs) and the treatment of CNS injury: advantages and possible caveats

One of the main research strategies to improve treatment for spinal cord injury involves the use of cell transplantation. This review looks at the advantages and possible caveats of using glial cells from the olfactory system in transplant-mediated repair. These glial cells, termed olfactory ensheathing cells (OECs), ensheath the axons of the olfactory receptor neurons. The primary olfactory system is an unusual tissue in that it can support neurogenesis throughout life. In addition, newly generated olfactory receptor neurons are able to grow into the CNS environment of the olfactory bulb tissue and reform synapses. It is thought that this unique regenerative property depends in part on the presence of OECs. OECs share some of the properties of both astrocytes and Schwann cells but appear to have advantages over these and other glial cells for CNS repair. In particular, OECs are less likely to induce hypertrophy of CNS astrocytes. As well as remyelinating demyelinated axons, OEC grafts appear to promote the restoration of functions lost following a spinal cord lesion. However, much of the evidence for this is based on behavioural tests, and the mechanisms that underlie their potential benefits in transplant-mediated repair remain to be clarified.

Neuregulin-2 is developmentally regulated and targeted to dendrites of central neurons

Neuregulin-1 (NRG-1) regulates numerous aspects of neural development and synaptic plasticity; the functions of NRG-2 and NRG-3 are presently unknown. As a first step toward understanding how NRGs contribute to distinct aspects of neural development and function, we characterized their regional and subcellular expression patterns in developing brain. The expression of NRG-1-3 mRNAs was compared postnatally (P0, P7, adult) by using in situ hybridization. NRG-1 expression is highest at birth, whereas NRG-2 mRNA levels increase with development; expression of both genes is restricted to distinct brain regions. In contrast, NRG-3 transcripts are abundant in most brain regions throughout development. NRG-2 antibodies were generated to analyze protein processing, expression, and subcellular distribution. As with NRG-1, the transmembrane NRG-2 proprotein is proteolytically processed in transfected HEK 293 cells and in neural tissues, and its ectodomain is exposed and accumulates on the neuron surface. Despite the structural similarities between NRG-1 and NRG-2, we unexpectedly found that NRG-2 colocalizes with MAP2 in proximal primary dendrites of hippocampal neurons in culture and in vivo, although it is not detectable in axons or in axon terminals. These findings were confirmed with NRG-2 ectodomain antisera and epitope-tagged recombinant protein. In cerebellum, NRG-2 colocalizes with calbindin in proximal dendrites and soma of Purkinje cells. In contrast, NRG-1 is highly expressed in axons of dissociated hippocampal neurons, as well as in somas and dendrites. The distinct temporal, regional, and subcellular expression of NRG-2 suggests its unique and nonredundant role in neural function.

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.

Gene targeting reveals multiple essential functions of the neuregulin signaling system during development of the neuroendocrine and nervous systems

Mice harboring targeted mutations in neuregulin-1 and its receptors (erbB2, erbB3, and erbB4) have been invaluable tools for testing the roles of these genes in vivo as well as for identifying unexpected functions for this signaling system. This review summarizes the advances in understanding the myriad functions of neuregulins in the nervous and neuroendocrine systems that have been revealed by examining gene-targeted mice.

Cell-intrinsic differences between stem cells from different regions of the peripheral nervous system regulate the generation of neural diversity

Stem cells in different regions of the nervous system give rise to different types of mature cells. This diversity is assumed to arise in response to local environmental differences, but the contribution of cell-intrinsic differences between stem cells has been unclear. At embryonic day (E)14, neural crest stem cells (NCSCs) undergo primarily neurogenesis in the gut but gliogenesis in nerves. Yet gliogenic and neurogenic factors are expressed in both locations. NCSCs isolated by flow-cytometry from E14 sciatic nerve and gut exhibited heritable, cell-intrinsic differences in their responsiveness to lineage determination factors. Gut NCSCs were more responsive to neurogenic factors, while sciatic nerve NCSCs were more responsive to gliogenic factors. Upon transplantation of uncultured NCSCs into developing peripheral nerves in vivo, sciatic nerve NCSCs gave rise only to glia, while gut NCSCs gave rise primarily to neurons. Thus, cell fate in the nerve was stem cell determined.

Mitogen-activated protein kinase-dependent and -independent routes control shedding of transmembrane growth factors through multiple secretases

Solubilization of a number of membrane proteins occurs by the action of cell-surface proteases, termed secretases. Recently, the activity of these secretases has been reported to be controlled by the extracellular signal-regulated kinases 1 and 2 (ERK1/ERK2) and the p38 mitogen-activated protein kinase (MAPK) routes. In the present paper, we show that shedding of membrane-anchored growth factors (MAGFs) may also occur through MAPK-independent routes. In Chinese-hamster ovary cells, cleavage induced by protein kinase C (PKC) stimulation was largely insensitive to inhibitors of the ERK1/ERK2 and p38 routes. Other reagents such as sorbitol or UV light stimulated MAGF cleavage independent of PKC. The action of sorbitol on cleavage was only partially prevented by the combined action of inhibitors of the p38 and ERK1/ERK2 routes, indicating that sorbitol can also stimulate shedding by MAPK-dependent and -independent routes. Studies in cells devoid of activity of the secretase tumour necrosis factor-alpha-converting enzyme (TACE) indicated that this protease had an essential role in PKC- and ERK1/ERK2-mediated shedding. However, secretases other than TACE may also cleave MAGFs since sorbitol could still induce shedding in these cells. These observations suggest that cleavage of MAGFs is a complex process in which multiple secretases, activated through different MAPK-dependent and -independent routes, are involved.

Neuregulin signaling via erbB receptor assemblies in the nervous system

Neuregulins (NRG) play important roles in the development, maintenance, and repair of the nervous system, with influences on neuronal migration, synaptogenesis, receptor subunit composition, and the proliferation/survival of oligodendrocytes and Schwann cells. However, the precise detail of how the NRGs signal through ErbB receptors, particularly at central synapses, is incomplete. The receptor kinase domain provides sites for association with adaptor proteins. In addition, evidence from recent reports suggests that ErbB2/4 receptors, through their C-terminal amino acids, can form specific associations with scaffolding proteins. The existence of such assemblies expands the range of signaling cascades available to the NRGs.