In situ hybridization reveals developmental regulation of ErbB1-4 mRNA expression in mouse midbrain: implication of ErbB receptors for dopaminergic neurons

Identification of diagnose related therapeutic targets of Danggui buxue decoction in Parkinson's disease

BACKGROUND

Parkinson's disease (PD) is the fastest growing neurological disease. Currently, there is no disease-modifying therapy to slow the progression of the disease. Danggui buxue decoction (DBD) is widely used in the clinic because of its therapeutic effect. However, little is known about the molecular mechanism of DBD against PD. This study intends to explore the possible molecular mechanisms involved in DBD treatment of PD based on network pharmacology, and provide potential research directions for future research.

METHODS

Firstly, the active components and target genes of DBD were screened from the traditional Chinese medicine systems pharmacology (TCMSP), DrugBank and UniProt database. Secondly, target genes of PD were identified from the (GEO) dataset, followed by identification of common target genes of DBD and PD. Thirdly, analysis of protein-protein interaction (PPI), functional enrichment and diagnosis was performed on common target genes, followed by correlation analysis between core target genes, immune cell, miRNAs, and transcription factors (TFs). Finally, molecular docking between core target genes and active components, and real-time PCR were performed.

RESULTS

A total of 72 common target genes were identified between target genes of DBD and target genes of PD. Among which, 11 target genes with potential diagnostic value were further identified, including TP53, AKT1, IL1B, MMP9, NOS3, RELA, MAPK14, HMOX1, TGFB1, NOS2, and ERBB2. The combinations with the best docking binding were identified, including kaempferol-AKT1/HMOX1/NOS2/NOS3, quercetin-AKT1/ERBB2/IL1B/HMOX1/MMP9/TP53/NOS3/TGFB1. Moreover, IL1B and NOS2 respectively positively and negatively correlated with neutrophil and Type 1 T helper cell. Some miRNA-core target gene regulatory pairs were identified, such as hsa-miR-185-5p-TP53/TGFB1/RELA/MAPK14/IL1B/ERBB2/AKT1 and hsa-miR-214-3p-NOS3. These core target genes were significantly enriched in focal adhesion, TNF, HIF-1, and ErbB signaling pathway.

CONCLUSION

Diagnostic TP53, AKT1, IL1B, MMP9, NOS3, RELA, MAPK14, HMOX1, TGFB1, NOS2, and ERBB2 may be considered as potential therapeutic targets of DBD in the treatment of PD.

ErbB2pY -1248 as a predictive biomarker for Parkinson's disease based on research with RPPA technology and in vivo verification

AIMS

This study aims to reveal a promising biomarker for Parkinson's disease (PD) based on research with reverse phase protein array (RPPA) technology for the first time and in vivo verification, which gains time for early intervention in PD, thus increasing the effectiveness of treatment and reducing disease morbidity.

METHODS AND RESULTS

We employed RPPA technology which can assess both total and post-translationally modified proteins to identify biomarker candidates of PD in a cellular PD model. As a result, the phosphorylation (pY-1248) of the epidermal growth factor receptor (EGFR) ErbB2 is a promising biomarker candidate for PD. In addition, lapatinib, an ErbB2 tyrosine kinase inhibitor, was used to verify this PD biomarker candidate in vivo. We found that lapatinib-attenuated dopaminergic neuron loss and PD-like behavior in the zebrafish PD model. Accordingly, the expression of ErbB2pY-1248 significantly increased in the MPTP-induced mouse PD model. Our results suggest that ErbB2pY-1248 is a predictive biomarker for PD.

CONCLUSIONS

In this study, we found that ErbB2pY-1248 is a predictive biomarker of PD by using RPPA technology and in vivo verification. It offers a new perspective on PD diagnosing and treatment, which will be essential in identifying individuals at risk of PD. In addition, this study provides new ideas for digging into biomarkers of other neurodegenerative diseases.

Treadmill Running Regulates Adult Neurogenesis, Spatial and Non-spatial Learning, Parvalbumin Neuron Activity by ErbB4 Signaling

Exercise can promote adult neurogenesis and improve symptoms associated with schizophrenia and other mental disorders via parvalbumin (PV)-positive GABAergic interneurons in the dentate gyrus ErbB4 is the receptor of neurotrophic factor neuregulin 1, expressed mostly in PV-positive interneurons. Whether ErbB4 in PV-positive neurons mediates the beneficial effect of exercise and adult neurogenesis on mental disorder needs to be further investigation. Here, we first conducted a four-week study on the effects of AG1478, an ErbB4 inhibitor, on memory and neurogenesis. AG1478 significantly impaired the performance in several memory tasks, including the T-maze, Morris water maze, and contextual fear conditioning, downregulated the expression of total ErbB4 (T-ErbB4) and the ratio of phosphate-ErbB4 (p-ErbB4) to T-ErbB4, and associated with neurogenesis impairment. Interestingly, AG1478 also appeared to decrease intracellular calcium levels in PV neurons, which could be reversed by exercise. These results suggest exercise may regulate adult neurogenesis and PV neuron activity through ErbB4 signaling. Overall, these findings provide further evidence of the importance of exercise for neurogenesis and suggest that targeting ErbB4 may be a promising strategy for improving memory and other cognitive functions in individuals with mental disorders.

The laterodorsal tegmentum-ventral tegmental area circuit controls depression-like behaviors by activating ErbB4 in DA neurons

Dopamine (DA) neurons in the ventral tegmental area (VTA) are critical to coping with stress. However, molecular mechanisms regulating their activity and stress-induced depression were not well understood. We found that the receptor tyrosine kinase ErbB4 in VTA was activated in stress-susceptible mice. Deleting ErbB4 in VTA or in DA neurons, or chemical genetic inhibition of ErbB4 kinase activity in VTA suppressed the development of chronic social defeat stress (CSDS)-induced depression-like behaviors. ErbB4 activation required the expression of NRG1 in the laterodorsal tegmentum (LDTg); LDTg-specific deletion of NRG1 inhibited depression-like behaviors. NRG1 and ErbB4 suppressed potassium currents of VTA DA neurons and increased their firing activity. Finally, we showed that acute inhibition of ErbB4 after stress attenuated DA neuron hyperactivity and expression of depression-like behaviors. Together, these observations demonstrate a critical role of NRG1-ErbB4 signaling in regulating depression-like behaviors and identify an unexpected mechanism by which the LDTg-VTA circuit regulates the activity of DA neurons.

Schizophrenia Animal Modeling with Epidermal Growth Factor and Its Homologs: Their Connections to the Inflammatory Pathway and the Dopamine System

Epidermal growth factor (EGF) and its homologs, such as neuregulins, bind to ErbB (Her) receptor kinases and regulate glial differentiation and dopaminergic/GABAergic maturation in the brain and are therefore implicated in schizophrenia neuropathology involving these cell abnormalities. In this review, we summarize the biological activities of the EGF family and its neuropathologic association with schizophrenia, mainly overviewing our previous model studies and the related articles. Transgenic mice as well as the rat/monkey models established by perinatal challenges of EGF or its homologs consistently exhibit various behavioral endophenotypes relevant to schizophrenia. In particular, post-pubertal elevation in baseline dopaminergic activity may illustrate the abnormal behaviors relevant to positive and negative symptoms as well as to the timing of this behavioral onset. With the given molecular interaction and transactivation of ErbB receptor kinases with Toll-like receptors (TLRs), EGF/ErbB signals are recruited by viral infection and inflammatory diseases such as COVID-19-mediated pneumonia and poxvirus-mediated fibroma and implicated in the immune-inflammatory hypothesis of schizophrenia. Finally, we also discuss the interaction of clozapine with ErbB receptor kinases as well as new antipsychotic development targeting these receptors.

Developmental, neurochemical, and behavioral analyses of ErbB4 Cyt-1 knockout mice

Neuregulins (NRGs) and their cognate neuronal receptor ERBB4, which is expressed in GABAergic and dopaminergic neurons, regulate numerous behaviors in rodents and have been identified as schizophrenia at-risk genes. ErbB4 transcripts are alternatively spliced to generate isoforms that either include (Cyt-1) or exclude (Cyt-2) exon 26, which encodes a cytoplasmic domain that imparts ErbB4 receptors the ability to signal via the phosphoinositide 3-kinase (PI3K)/protein kinase B (Akt) pathway. Although ErbB4 Cyt-1/2 isoforms have been studied in transfected cultured cells, their functions in vivo remain unknown. Here, we generated ErbB4-floxed (ErbB4-Cyt1^fl/fl ) mice to investigate the effects of germline (constitutive) and conditional (acute) deletions of the Cyt-1 exon. Overall receptor mRNA levels remain unchanged in germline ErbB4 Cyt-1 knockouts (Cyt-1 KOs), with all transcripts encoding Cyt-2 variants. In contrast to mice lacking all ErbB4 receptor function, GABAergic interneuron migration and number are unaltered in Cyt-1 KOs. However, basal extracellular dopamine (DA) levels in the medial prefrontal cortex are increased in Cyt-1 heterozygotes. Despite these neurochemical changes, Cyt-1 heterozygous and homozygous mice do not manifest behavioral abnormalities previously reported to be altered in ErbB4 null mice. To address the possibility that Cyt-2 variants compensate for the lack of Cyt-1 during development, we microinjected an adeno-associated virus expressing Cre-recombinase (AAV-Cre) into the DA-rich ventral tegmental area of adult ErbB4-Cyt1^fl/fl mice to acutely target exon 26. These conditional Cyt-1 KOs were found to exhibit behavioral abnormalities in the elevated plus maze and startle response, consistent with the idea that late exon 26 ablations may circumvent compensation by Cyt-2 variants. Taken together, our observations indicate that ErbB4 Cyt-1 function in vivo is important for DA balance and behaviors in adults.

Anxiety-like behavior in female mice is modulated by STAT3 signaling in midbrain dopamine neurons

The central signaling actions of cytokines are mediated by signal transducer and activator of transcription (STAT3). STAT3 activation plays a pivotal role in the behavioral responses to the adiposity hormone leptin, including in midbrain dopamine (DA) neurons where it mediates the influence of leptin to diminish physical activity and running reward in male mice. Leptin also has anxiolytic effects which have been tied to the mesolimbic DA system. To assess the contribution of STAT3 signaling in mesolimbic DA neurons on feeding, mesolimbic DA tone and anxiodepressive behaviors in female mice, we generated DA-specific STAT3 knockout mice by crossing mice expressing Cre under the control of the dopamine transporter with STAT3-LoxP mice. Feeding, locomotion, wheel running, conditioned place preference for palatable food and amphetamine locomotor sensitization were unaffected by DA-specific STAT3 deletion. Conversely, knockout mice exhibited heightened anxiety-like behavior (open field test and elevated plus maze) along with increased basal and stress-induced plasma corticosterone, whereas indices of behavioral despair (forced swim and tail-suspension tasks) were unchanged. In accordance with biochemical evidence of increased D1 receptor signaling (phospho-DARPP32_Thr34) in the central nucleus of the amygdala (CeA) of knockout mice, local microinjections of a D1 receptor antagonist reversed the anxiogenic phenotype of knockout mice. In addition to alluding to sex differences in the signaling mechanisms mediating anxiety-like behavior, our findings suggest that activation of STAT3 in midbrain dopamine neurons projecting to the CeA dampens anxiety in a D1R-dependent manner in female mice.

ErbB4 promotes inhibitory synapse formation by cell adhesion, independent of its kinase activity

The precise control of the nervous system function under the vitality of synapses is extremely critical. Efforts have been taken to explore the underlying cellular and molecular mechanisms for synapse formation. Cell adhesion molecules have been found important for synapse assembly in the brain. Many trans-adhesion complexes have been identified to modulate excitatory synapse formation. However, little is known about the synaptogenic mechanisms for inhibitory synapses. ErbB4 is a receptor tyrosine kinase enriched in interneurons. Here, we showed that overexpressing ErbB4 in HEK293T cells induced gephyrin or GABA_AR α1 puncta in co-cultured primary hippocampal neurons. This induction of ErbB4 was independent of its kinase activity. K751M, a kinase-dead mutant of ErbB4, can also induce gephyrin or GABA_AR α1 puncta in the co-culture system. We further constructed K751M knock-in mice and found that the homozygous were viable at birth and fertile without changes in gross brain structure. The number of interneurons and inhibitory synapses onto pyramidal neurons (PyNs) were comparable between K751M and wild-type mice but decreased in ErbB4-Null mice. Moreover, ErbB4 can interact in trans with Slitrk3, a transmembrane postsynaptic protein at inhibitory synapses, through the extracellular RLD domain of ErbB4. The deletion of RLD diminished the induction of gephyrin or GABA_AR α1 puncta by ErbB4. Finally, disruption of ErbB4-Slitrk3 interaction through neutralization of Slitrk3 by secretable RLD decreased inhibitory synapses onto PyNs and impaired GABAergic transmission. These results identify that ErbB4, as a cell adhesion molecule, promotes inhibitory synapse formation onto PyNs by interacting with Slitrk3 and in a kinase-independent manner, providing an unexpected mechanism of ErbB4 in inhibitory synapse formation.

Growth Factors as Axon Guidance Molecules: Lessons From in vitro Studies

Growth cones at the tips of extending axons navigate through developing organisms by probing extracellular cues, which guide them through intermediate steps and onto final synaptic target sites. Widespread focus on a few guidance cue families has historically overshadowed potentially crucial roles of less well-studied growth factors in axon guidance. In fact, recent evidence suggests that a variety of growth factors have the ability to guide axons, affecting the targeting and morphogenesis of growth cones in vitro. This review summarizes in vitro experiments identifying responses and signaling mechanisms underlying axon morphogenesis caused by underappreciated growth factors.

Striatal transcriptome changes linked to drug-induced repetitive behaviors

Disruptive or excessive repetitive motor patterns (stereotypies) are cardinal symptoms in numerous neuropsychiatric disorders. Stereotypies are also evoked by psychomotor stimulants such as amphetamine. The acquisition of motor sequences is paralleled by changes in activity patterns in the striatum, and stereotypies have been linked to abnormal plasticity in these reinforcement-related circuits. Here, we designed experiments in mice to identify transcriptomic changes that underlie striatal plasticity occurring alongside the development of drug-induced stereotypic behavior. We identified three schedules of amphetamine treatment inducing different degrees of stereotypy and used bulk RNAseq to compare striatal gene expression changes among groups of mice treated with the different drug-dose schedules and vehicle-treated, cage-mate controls. Mice were identified as naïve, sensitized, or tolerant to drug-induced stereotypy. All drug-treated groups exhibited expression changes in genes that encode members of the extracellular signal-regulated kinase (ERK) cascades known to regulate psychomotor stimulant responses. In the sensitized group with the most prolonged stereotypy, we found dysregulation of 20 genes that were not changed in other groups. Gene set enrichment analysis indicated highly significant overlap with genes regulated by neuregulin 1 (Nrg1). Nrg1 is known to be a schizophrenia and autism susceptibility gene that encodes a ligand for Erb-B receptors, which are involved in neuronal migration, myelination, and cell survival, including that of dopamine-containing neurons. Stimulant abuse is a risk factor for schizophrenia onset, and these two disorders share behavioral stereotypy phenotypes. Our results raise the possibility that drug-induced sensitization of the Nrg1 signaling pathway might underlie these links.

Association between epidermal growth factor receptor gene polymorphisms and susceptibility to Parkinson's disease

OBJECTIVE

The progressive loss of dopaminergic neurons in the mesencephalic substantia nigra is recognized as an important pathological feature of Parkinson's disease (PD). Several research studies have suggested that the EGFR signaling pathway may play a significant role in the survival and functional development of dopaminergic neurons. Therefore, genetic variations in these pathways may be related with PD susceptibility. The aim of our study was to explore the association between selected single nucleotide polymorphisms (SNPs) of the epidermal growth factor receptor (EGFR) gene, including rs730437, rs3752651 and rs11506105, and susceptibility to Parkinson's disease in a Han Chinese population.

METHODS

A total of 870 Han Chinese subjects, including 435 PD patients and 435 healthy controls, were enrolled in this case-control study. Peripheral blood was obtained from all subjects for DNA extraction, and selected SNPs (rs730437, rs3752651, rs11506105) of the EGFR gene were genotyped using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). Differences in the frequencies of genotype and allele gene polymorphisms between patients with PD and healthy controls were analyzed using the Chi-square test. Logistic regression analysis was applied for calculating the odds ratios (ORs) and 95 % confidence intervals (CIs) to evaluate potential associations.

RESULTS

We observed statistically significant differences in rs730437 in the additive models (AC vs. AA: P = 0.047), dominant models (CC + AC vs. AA: P = 0.024) and alleles (C vs. A: P = 0.018). Further subgroup analyses indicated that the C allele of rs730437 showed lower prevalence in the EOPD, compared with matched controls (P = 0.005). The frequency of the GG genotype and G allele for rs11506105 was lower in PD subjects than in healthy controls in the entire study population (P = 0.028, P = 0.034, respectively) and female group (P = 0.024, P = 0.007, respectively). No significant association was found between rs3752651 polymorphism and PD susceptibility in either the whole or subgroup analyses. The analysis of gene haplotypes revealed that the AAT haplotype was related with PD susceptibility.

CONCLUSION

The rs730437 and rs11506105 polymorphisms, but not the rs3752651 polymorphism, of the EGFR gene may be related with susceptibility to PD in a Han Chinese population. An investigation using a larger sample size is warranted to further analyze potential associations between the EGFR gene and PD.

Neuregulins 1, 2, and 3 Promote Early Neurite Outgrowth in ErbB4-Expressing Cortical GABAergic Interneurons

The neuregulins (Nrgs 1-4) are a family of signaling molecules that play diverse roles in the nervous system. Nrg1 has been implicated in the formation of synapses and in synaptic plasticity. Previous studies have shown Nrg1 can affect neurite outgrowth in several neuronal populations, while the role of Nrg2 and Nrg3 in this process has remained understudied. The Nrgs can bind and activate the ErbB4 receptor tyrosine kinase which is preferentially expressed in GABAergic interneurons in the rodent hippocampus and cerebral cortex. In the present study, we evaluated the effects of Nrgs 1, 2, and 3 on neurite outgrowth of dissociated rat cortical ErbB4-positive (⁺)/GABA⁺ interneurons in vitro. All three Nrgs were able to promote neurite outgrowth during the first 2 days in vitro, with increases detected for both the axon (116-120%) and other neurites (100-120%). Increases in the average number of primary and secondary neurites were also observed. Treatment with the Nrgs for an additional 3 days promoted an increase in axonal length (86-96%), with only minimal effects on the remaining neurites (8-13%). ErbB4 expression persisted throughout the dendritic arbor and cell soma at all stages examined, while its expression in the axon was transient and declined with cell maturation. ErbB4 overexpression in GABAergic neurons promoted neurite outgrowth, an effect that was potentiated by Nrg treatment. These results show that Nrgs 1, 2, and 3 are each capable of influencing dendritic and axonal growth at early developmental stages in GABAergic neurons grown in vitro.

Post-pubertal Difference in Nigral Dopaminergic Cells Firing in the Schizophrenia Model Prepared by Perinatal Challenges of a Cytokine, EGF

Schizophrenia in humans typically develops during and after adolescence; however, the biological underpinning for the specificity of this onset time window remains to be determined. In the present study, we investigated this knowledge gap using our own animal model for schizophrenia. Rodents and monkeys challenged with a cytokine, epidermal growth factor (EGF), as neonates are known to exhibit various behavioral and cognitive abnormalities at the post-pubertal stage. We used the EGF-challenged mice as an animal model for schizophrenia to evaluate the electrophysiological impact of this modeling on nigral dopamine neurons before and after puberty. In vivo single unit recording revealed that the burst firing of putative dopamine neurons in substantia nigra pars compacta was significantly higher in the post-pubertal stage of the EGF model than in that of control mice; in contrast, this difference was not observed in the pre-pubertal stage. The increase in burst firing was accompanied by a decline in Ca²⁺-activated K⁺ (I_SK) currents, which influence the firing pattern of dopamine neurons. In vivo local application of the SK channel blocker apamin (80 μM) to the substantia nigra was less effective at increasing burst firing in the EGF model than in control mice, suggesting the pathologic role of the I_SK decrease in this model. Thus, these results suggest that the aberrant post-pubertal hyperactivity of midbrain dopaminergic neurons is associated with the temporal specificity of the behavioral deficit of this model, and support the hypothesis that this dopaminergic aberration could be implicated in the adolescent onset of schizophrenia.

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.

Impaired social discrimination behavior despite normal social approach by kallikrein-related peptidase 8 knockout mouse

For social mammals, recognition of conspecifics and discrimination of each other (social memory) is crucial to living in a stable colony. Here, we investigated whether kallikrein-related peptidase 8 (KLK8)-neuregulin 1 (NRG1)-ErbB signaling is crucial for social discrimination behavior using the social discrimination three chamber behavioral test. Klk8 knockout mice (NRG1-deactivated mice) exhibited normal social approach but impaired social discrimination. Intraventricular injection of recombinant NRG1_177-246 into Klk8 knockout mice reversed this impaired social discrimination. This study reveals that KLK8 is a key regulator of NRG1-ErbB signaling, which contributes to social discrimination behavior.

mGluR1-Dependent Long Term Depression in Rodent Midbrain Dopamine Neurons Is Regulated by Neuregulin 1/ErbB Signaling

Increasing evidence demonstrates that the neurotrophic factor Neuregulin 1 (NRG1) and its receptors, ErbB tyrosine kinases, modulate midbrain dopamine (DA) transmission. We have previously reported that NRG1/ErbB signaling is essential for proper metabotropic glutamate receptors 1 (mGluR1) functioning in midbrain DA neurons, thus the functional interaction between ErbB receptors and mGluR1 regulates neuronal excitation and in vivo striatal DA release. While it is widely recognized that mGluR1 play a pivotal role in long-term modifications of synaptic transmission in several brain areas, specific mGluR1-dependent forms of synaptic plasticity in substantia nigra pars compacta (SNpc) DA neurons have not been described yet. Here, first we aimed to detect and characterize mGluR1-dependent glutamatergic long-term depression (LTD) in SNpc DA neurons. Second, we tested the hypothesis that endogenous ErbB signaling, by affecting mGluR1, fine-tunes glutamatergic synaptic plasticity in DA cells. We found that either pharmacological or synaptic activation of mGluR1 causes an LTD of AMPAR-mediated transmission in SNpc DA neurons from mice and rat slices, which is reliant on endogenous NRG1/ErbB signaling. Indeed, LTD is counteracted by a broad spectrum ErbB inhibitor. Moreover, the intracellular injection of pan-ErbB- or ErbB2 inhibitors inside DA neurons reduces mGluR1-dependent LTD, suggesting an involvement of ErbB2/ErbB4-containing receptors. Interestingly, exogenous NRG1 fosters LTD expression during minimal mGluRI activation. These results enlarge our cognizance on mGluR1 relevance in the induction of a novel form of long-term synaptic plasticity in SNpc DA neurons and describe a new NRG1/ErbB-dependent mechanism shaping glutamatergic transmission in DA cells. This might have important implications either in DA-dependent behaviors and learning/memory processes or in DA-linked diseases.

Neuregulin-2 ablation results in dopamine dysregulation and severe behavioral phenotypes relevant to psychiatric disorders

Numerous genetic and functional studies implicate variants of Neuregulin-1 (NRG1) and its neuronal receptor ErbB4 in schizophrenia and many of its endophenotypes. Although the neurophysiological and behavioral phenotypes of NRG1 mutant mice have been investigated extensively, practically nothing is known about the function of NRG2, the closest NRG1 homolog. We found that NRG2 expression in the adult rodent brain does not overlap with NRG1 and is more extensive than originally reported, including expression in the striatum and medial prefrontal cortex (mPFC), and therefore generated NRG2 knockout mice (KO) to study its function. NRG2 KOs have higher extracellular dopamine levels in the dorsal striatum but lower levels in the mPFC; a pattern with similarities to dopamine dysbalance in schizophrenia. Like ErbB4 KO mice, NRG2 KOs performed abnormally in a battery of behavioral tasks relevant to psychiatric disorders. NRG2 KOs exhibit hyperactivity in a novelty-induced open field, deficits in prepulse inhibition, hypersensitivity to amphetamine, antisocial behaviors, reduced anxiety-like behavior in the elevated plus maze and deficits in the T-maze alteration reward test-a task dependent on hippocampal and mPFC function. Acute administration of clozapine rapidly increased extracellular dopamine levels in the mPFC and improved alternation T-maze performance. Similar to mice treated chronically with N-methyl-d-aspartate receptor (NMDAR) antagonists, we demonstrate that NMDAR synaptic currents in NRG2 KOs are augmented at hippocampal glutamatergic synapses and are more sensitive to ifenprodil, indicating an increased contribution of GluN2B-containing NMDARs. Our findings reveal a novel role for NRG2 in the modulation of behaviors with relevance to psychiatric disorders.

ErbB signaling antagonist ameliorates behavioral deficit induced by phencyclidine (PCP) in mice, without affecting metabolic syndrome markers

Schizophrenia is a severe syndrome that affects about 1% of the world population. Since the mid-1950s, antipsychotics have been used to treat schizophrenia with preference for treating positive symptoms; however, their tolerance level is low, there are numerous side effects, and only some patients respond to the treatment. Antipsychotic medications that are more effective, better tolerated, and with fewer adverse effects are urgently needed. Given the accumulating evidence of the role filled by the ErbB signaling network in the biology of the dopamine, GABA, and glutamate systems, and in the etiology of schizophrenia, we hypothesized that the ErbB network is a candidate for development of a novel agent through which various symptoms of schizophrenia and other psychiatric disorders might be treated. Herein, we studied, in mice, the capability of blocking the ErbB signaling, in comparison with the atypical antipsychotic drug clozapine, to counter schizophrenia-like behavior induced by acute and sub-chronic phencyclidine (PCP), and determined whether inhibition of the ErbB networks induced weight gain and affected social and exploratory behavior, and metabolic syndrome markers. We demonstrated that administration of the pan-ErbB inhibitor JNJ28871063 (JNJ) reduced the level of activity in the open field induced by an acute injection of PCP. Moreover, the ability of JNJ to attenuate the effect of PCP is as effective as clozapine. In addition and like clozapine, JNJ normalized social behavior impairment induced by sub-chronic PCP and stress. Adult JNJ-treated mice displayed normal sociability and exploratory behavior, and their serum cholesterol, LDL, and HDL levels were lower than in the saline-treated mice. Sub-chronic treatment did not affect weight gain, glucose levels, and the activity of hepatic enzymes catalase and SOD. These data suggest that treatment with JNJ attenuates abnormal behaviors induced by PCP, and has similar effects as the antipsychotic drug clozapine, with no adverse effects. Thus, the ErbB signaling can serve as a new starting point for non-dopaminergic-based drug development of schizophrenia.

A role for ErbB signaling in the induction of reactive astrogliosis

Reactive astrogliosis is a hallmark of many neurological disorders, yet its functions and molecular mechanisms remain elusive. Particularly, the upstream signaling that regulates pathological responses of astrocytes is largely undetermined. We used a mouse traumatic brain injury model to induce astrogliosis and revealed activation of ErbB receptors in reactive astrocytes. Moreover, cell-autonomous inhibition of ErbB receptor activity in reactive astrocytes by a genetic approach suppressed hypertrophic remodeling possibly through the regulation of actin dynamics. However, inhibiting ErbB signaling in reactive astrocytes did not affect astrocyte proliferation after brain injury, although it aggravated local inflammation. In contrast, active ErbB signaling in mature astrocytes of various brain regions in mice was sufficient to initiate reactive responses, reproducing characterized molecular and cellular features of astrogliosis observed in injured or diseased brains. Further, prevalent astrogliosis in the brain induced by astrocytic ErbB activation caused anorexia in animals. Therefore, our findings defined an unrecognized role of ErbB signaling in inducing reactive astrogliosis. Mechanistically, inhibiting ErbB signaling in reactive astrocytes prominently reduced Src and focal adhesion kinase (FAK) activity that is important for actin remodeling, although ErbB signaling activated multiple downstream signaling proteins. The discrepancies between the results from loss- and gain-of-function studies indicated that ErbB signaling regulated hypertrophy and proliferation of reactive astrocytes by different downstream signaling pathways. Our work demonstrated an essential mechanism in the pathological regulation of astrocytes and provided novel insights into potential therapeutic targets for astrogliosis-implicated diseases.

Translating advances in the molecular basis of schizophrenia into novel cognitive treatment strategies

The presence and severity of cognitive symptoms, including working memory, executive dysfunction and attentional impairment, contributes materially to functional impairment in schizophrenia. Cognitive symptoms have proved to be resistant to both first- and second-generation antipsychotic drugs. Efforts to develop a consensus set of cognitive domains that are both disrupted in schizophrenia and are amenable to cross-species validation (e.g. the National Institute of Mental Health Cognitive Neuroscience Treatment Research to Improve Cognition in Schizophrenia and Research Domain Criteria initiatives) are an important step towards standardization of outcome measures that can be used in preclinical testing of new drugs. While causative genetic mutations have not been identified, new technologies have identified novel genes as well as hitherto candidate genes previously implicated in the pathophysiology of schizophrenia and/or mechanisms of antipsychotic efficacy. This review comprises a selective summary of these developments, particularly phenotypic data arising from preclinical genetic models for cognitive dysfunction in schizophrenia, with the aim of indicating potential new directions for pro-cognitive therapeutics. Linked Articles This article is part of a themed section on Pharmacology of Cognition: a Panacea for Neuropsychiatric Disease? To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v174.19/issuetoc.

Epidermal growth factor signals attenuate phenotypic and functional development of neocortical GABA neurons

Phenotypic development of neocortical GABA neurons is highly plastic and promoted by various neurotrophic factors such as neuregulin-1. A subpopulation of GABA neurons expresses not only neuregulin receptor (ErbB4) but also epidermal growth factor (EGF) receptor (ErbB1) during development, but the neurobiological action of EGF on this cell population is less understood than that of neuregulin-1. Here, we examined the effects of exogenous EGF on immature GABA neurons both in culture and in vivo and also explored physiological consequences in adults. We prepared low density cultures from the neocortex of rat embryos and treated neocortical neurons with EGF. EGF decreased protein levels of glutamic acid decarboxylases (GAD65 and GAD67), and EGF influences on neuronal survival and glial proliferation were negligible or limited. The EGF treatment also diminished the frequency of miniature inhibitory postsynaptic currents (mIPSCs). In vivo administration of EGF to mouse pups reproduced the above GABAergic phenomena in neocortical culture. In EGF-injected postnatal mice, GAD- and parvalbumin-immunoreactivities were reduced in the frontal cortex. In addition, postnatal EGF treatment decreased mIPSC frequency in, and the density of, GABAergic terminals on pyramidal cells. Although these phenotypic influences on GABA neurons became less marked during development, it later resulted in the reduced β- and γ-powers of sound-evoked electroencephalogram in adults, which is regulated by parvalbumin-positive GABA neurons and implicated in the schizophrenia pathophysiology. These findings suggest that, in contrast to the ErbB4 ligand of neuregulin-1, the ErbB1 ligand of EGF exerts unique maturation-attenuating influences on developing cortical GABAergic neurons.

Receptor tyrosine kinases play a significant role in human oligodendrocyte inflammation and cell death associated with the Lyme disease bacterium Borrelia burgdorferi

Background

In previous studies, human oligodendrocytes were demonstrated to undergo apoptosis in the presence of Borrelia burgdorferi under an inflammatory milieu. Subsequently, we determined that the MEK/ERK pathway played a significant role in triggering downstream inflammation as well as apoptosis. However, the identity of receptors triggered by exposure to B. burgdorferi and initiating signaling events was unknown.

Methods

In this study, we explored the role of several TLR and EGFR/FGFR/PDGFR tyrosine kinase pathways in inducing inflammation in the presence of B. burgdorferi, using siRNA and/or inhibitors, in MO3.13 human oligodendrocytes. Cell death and apoptosis assays were also carried out in the presence or absence of specific receptor inhibitors along with the bacteria to determine the role of these receptors in apoptosis induction. The expression pattern of specific receptors with or without B. burgdorferi was also determined.

Results

TLRs 2 and 5 had a minimal role in inducing inflammation, particularly IL-6 production. Rather, their effect was mostly inhibitory, with TLR2 downregulation significantly upregulating CXCL8, and CXCL (1,2,3) levels, and TLR5 likely having a similar role in CXCL8, CXCL(1,2,3), and CCL5 levels. TLR4 contributed mostly towards CCL5 production. On the other hand, inhibition of all three EGF/FGF/PDGF receptors significantly downregulated all five of the inflammatory mediators tested even in the presence of B. burgdorferi. Their inhibition also downregulated overall cell death and apoptosis levels. The expression pattern of these receptors, as assessed by immunohistochemistry indicated that the PDGFRβ receptor was the most predominantly expressed receptor, followed by FGFR, although no significant differences were discernible between presence and absence of bacteria. Interestingly, inhibition of individual EGFR, FGFR, or PDGFR receptors did not indicate an individual role for any of these receptors in the overall downregulation of pathogenesis. Contrarily, suppression of FGFR signaling alone in the presence of bacteria significantly upregulated inflammatory mediator levels indicating that it might control an inhibitory pathway when triggered individually.

Conclusions

Unlike TLRs, EGF/FGF/PDGF receptors collectively play a significant role in the inflammation and apoptosis of human oligodendrocytes as mediated by B. burgdorferi. It is likely that these three receptors need to be triggered simultaneously to achieve this effect.

Phospholipase C Beta 1: a Candidate Signature Gene for Proneural Subtype High-Grade Glioma

Phospholipase C beta 1 (PLCβ1) expresses in gliomas and cultured glial cells, but its expression is barely detectable in normal glial cells. We analyzed data from Gene Expression Omnibus (GEO-GDSxxx), The Cancer Genome Atlas (TCGA), and the Repository for Molecular Brain Neoplasia Data (REMBRANDT) to explore the potential role of PLCβ1 as a biomarker in high-grade glioma (HGG). PLCβ1 expression is significantly higher in grade III gliomas than that in grade IV gliomas from GDS1815 (n = 24 vs. 76), GDS1962 (n = 19 vs. 81), and GDS1975 (n = 26 vs. 59). In GDS1815, PLCβ1 expression correlates with several known proneural (PN) signature genes; its expression from PN subtype (n = 15) is significantly higher than that from mesenchymal (Mes) subtype (n = 33) HGG. In GDS1962, PLCβ1 expression is the highest in nontumor brain tissue (n = 23) and is significantly higher than its expression in grade II gliomas [astrocytomas (n = 7) and oligodendrogliomas (n = 37)]. A Kaplan-Meier survival curve from a REMBRANDT cohort demonstrates that glioma patients with intermediate PLCβ1 expression (n = 103) survived significantly longer than PLCβ1 downregulated (2X) groups (n = 226). From TCGA data, PLCβ1 RNA-Seq signal inversely correlates with the pathological grades, and PLCβ1 expression in PN (n = 8) is of significantly higher levels than that in Mes (n = 8) subtypes of glioblastoma. The top 50 % of PLCβ1 expression subgroup (n = 294) of gliomas (grades II to IV merged) survived significantly longer than the low 50 percentile of the PLCβ1 expression subgroup (n = 293). p values are less than 0.05 for all these analyses. We conclude that PLCβ1 is a candidate signature gene for PN subtype HGG, and its expression inversely correlates with glioma pathological grade and is a potential prognostic factor.

Expression and Function of the Epidermal Growth Factor Receptor in Physiology and Disease

The epidermal growth factor receptor (EGFR) is the prototypical member of a family of membrane-associated intrinsic tyrosine kinase receptors, the ErbB family. EGFR is activated by multiple ligands, including EGF, transforming growth factor (TGF)-α, HB-EGF, betacellulin, amphiregulin, epiregulin, and epigen. EGFR is expressed in multiple organs and plays important roles in proliferation, survival, and differentiation in both development and normal physiology, as well as in pathophysiological conditions. In addition, EGFR transactivation underlies some important biologic consequences in response to many G protein-coupled receptor (GPCR) agonists. Aberrant EGFR activation is a significant factor in development and progression of multiple cancers, which has led to development of mechanism-based therapies with specific receptor antibodies and tyrosine kinase inhibitors. This review highlights the current knowledge about mechanisms and roles of EGFR in physiology and disease.

Perinatal Exposure to Neuregulin-1 Results in Disinhibition of Adult Midbrain Dopaminergic Neurons: Implication in Schizophrenia Modeling

Aberrant neuregulin-1 (NRG1) signals are suggested to associate with the neuropathophysiology of schizophrenia. Employing a mouse schizophrenia model established by neonatal neuregulin-1 challenge, we analysed postpubertal consequence of the NRG1 pretreatment for the electrophysiological property of nigral dopamine neurons. In vivo single unit recordings from anaesthetized NRG1-pretreated mice revealed increased spike bursting of nigral dopamine neurons. In slice preparations from NRG1-pretreated mice, spontaneous firing was elevated relative to controls. The relative increase in firing rates was abolished by a GABA_A receptor antagonist. Whole-cell recording showed that perinatal NRG1 pretreatment diminished inhibitory miniature synaptic currents as well as GABA_A receptor sensitivity. These results collectively suggest that perinatal exposure to neuregulin-1 results in the disinhibition of nigral dopamine neurons to influence their firing properties at the adult stage when the behavioral deficits are evident.

Pathological Implications of Oxidative Stress in Patients and Animal Models with Schizophrenia: The Role of Epidermal Growth Factor Receptor Signaling

Proinflammatory cytokines perturb brain development and neurotransmission and are implicated in various psychiatric diseases, such as schizophrenia and depression. These cytokines often induce the production of reactive oxygen species (ROS) and regulate not only cell survival and proliferation but also inflammatory process and neurotransmission. Under physiological conditions, ROS are moderately produced in mitochondria but are rapidly scavenged by reducing agents in cells. However, brain injury, ischemia, infection, or seizure-like neural activities induce inflammatory cytokines and trigger the production of excessive amounts of ROS, leading to abnormal brain functions and psychiatric symptoms. Protein phosphatases, which are involved in the basal silencing of cytokine receptor activation, are the major targets of ROS. Consistent with this, several ROS scavengers, such as polyphenols and unsaturated fatty acids, attenuate both cytokine signaling and psychiatric abnormalities. In this review, we list the inducers, producers, targets, and scavengers of ROS in the brain and discuss the interaction between ROS and cytokine signaling implicated in schizophrenia and its animal models. In particular, we present an animal model of schizophrenia established by perinatal exposure to epidermal growth factor and illustrate the pathological role of ROS and antipsychotic actions of ROS scavengers, such as emodin and edaravone.

Neuroteratology and Animal Modeling of Brain Disorders

Over the past 60 years, a large number of selective neurotoxins were discovered and developed, making it possible to animal-model a broad range of human neuropsychiatric and neurodevelopmental disorders. In this paper, we highlight those neurotoxins that are most commonly used as neuroteratologic agents, to either produce lifelong destruction of neurons of a particular phenotype, or a group of neurons linked by a specific class of transporter proteins (i.e., dopamine transporter) or body of receptors for a specific neurotransmitter (i.e., NMDA class of glutamate receptors). Actions of a range of neurotoxins are described: 6-hydroxydopamine (6-OHDA), 6-hydroxydopa, DSP-4, MPTP, methamphetamine, IgG-saporin, domoate, NMDA receptor antagonists, and valproate. Their neuroteratologic features are outlined, as well as those of nerve growth factor, epidermal growth factor, and that of stress. The value of each of these neurotoxins in animal modeling of human neurologic, neurodegenerative, and neuropsychiatric disorders is discussed in terms of the respective value as well as limitations of the derived animal model. Neuroteratologic agents have proven to be of immense importance for understanding how associated neural systems in human neural disorders may be better targeted by new therapeutic agents.

Gender differences in cognitive deficits in schizophrenia with and without diabetes

This study investigated gender differences in cognition in schizophrenia with and without diabetes. Cognition was assessed in 263 individuals with schizophrenia with age range (40-68): 67 males and 34 females with schizophrenia with diabetes; and 125 males and 37 females with schizophrenia without diabetes according to the Repeatable Battery for the Assessment of Neuropsychological Status (RBANS). Fasting glucose, hemoglobin A1c (HbA1c) and lipid levels were measured. Results showed that male individuals performed worse on most cognitive tasks, especially attention, in schizophrenia with than without diabetes. This result was not observed in female individuals. Also, individuals of both genders showed higher fasting glucose and HbA1c in schizophrenia with than without diabetes. In schizophrenia with diabetes, males had significantly worse cognition than females in all cognitive domains. Higher HbA1c, lower high-density lipoprotein, and an earlier age of onset of schizophrenia were found in males compared with female individuals. HbA1c was negatively associated with attention and the RBANS total score for males but not for females. In schizophrenia without diabetes, males showed worse performance in immediate and delayed memory than females. This study support cognition was worse for males with schizophrenia irrespective of whether they have diabetes. However, diabetes exemplified the gender differences, especially in attention.

Neuregulin 1 signalling modulates mGluR1 function in mesencephalic dopaminergic neurons

Neuregulin 1 (NRG1) is a trophic factor that has an essential role in the nervous system by modulating neurodevelopment, neurotransmission and synaptic plasticity. Despite the evidence that NRG1 and its receptors, ErbB tyrosine kinases, are expressed in mesencephalic dopaminergic nuclei and their functional alterations are reported in schizophrenia and Parkinson's disease, the role of NRG1/ErbB signalling in dopaminergic neurons remains unclear. Here we found that NRG1 selectively increases the metabotropic glutamate receptor 1 (mGluR1)-activated currents by inducing synthesis and trafficking to membrane of functional receptors and stimulates phosphatidylinositol 3-kinase-Akt-mammalian target of rapamycin (PI3K-Akt-mTOR) pathway, which is required for mGluR1 function. Notably, an endogenous NRG1/ErbB tone is necessary to maintain mGluR1 function, by preserving its surface membrane expression in dopaminergic neurons. Consequently, it enables striatal mGluR1-induced dopamine outflow in in vivo conditions. Our results identify a novel role of NRG1 in the dopaminergic neurons, whose functional alteration might contribute to devastating diseases, such as schizophrenia and Parkinson's disease.

EGFR signaling upregulates surface expression of the GluN2B-containing NMDA receptor and contributes to long-term potentiation in the hippocampus

N-methyl-d-aspartate receptors (NMDARs) have been known to be regulated by various receptor tyrosine kinases. Activation of epidermal growth factor receptor (EGFR) specifically increases NMDAR-mediated currents and enhances long-term potentiation (LTP) in the hippocampus. However, the mechanism through which EGFR regulates NMDARs remains to be elucidated. In this study we found that EGFR was highly expressed in the hippocampus and mainly localized in the non-synaptic region including the soma and neurites of cultured hippocampal neurons. EGFR activation led to an increase in ifenprodil-sensitive NMDAR currents. Consistent with this, we also observed that surface expression of GluN2B-containing NMDAR was upregulated. Our biochemical data from hippocampal slices and hippocampal cultured neurons demonstrated that EGF treatment in vitro significantly increased phosphorylation of the GluN2B subunit at Y1472 with a coincidental activation of Src family kinases (SFKs). EGFR blockade with a specific antagonist BIBX-1382 attenuated an increase of GluN2B in the postsynaptic density during high-frequency stimulation (HFS)-induced LTP. Moreover, BIBX blockade significantly impaired HFS-induced LTP. In conclusion, our findings suggest that EGFR signaling upregulates NMDARs through modification of the GluN2B subunit, and is required for HFS-induced LTP in the hippocampus.

Systemically administered neuregulin-1β1 rescues nigral dopaminergic neurons via the ErbB4 receptor tyrosine kinase in MPTP mouse models of Parkinson's disease

Previously, we demonstrated that systemically injected extracellular domain of neuregulin-1β1 (Nrg1β1), a nerve growth and differentiation factor, passes the blood-brain barrier and rescues dopaminergic neurons of substantia nigra in the 6-hydroxydopamine-mouse model of Parkinson's disease (PD). Here, we studied the effects of peripherally administered Nrg1β1 in another toxin-based mouse model of PD. For this purpose, (i) nigrostriatal pathway injury was induced by treatment of adult wild-type mice with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) in acute and subchronic paradigms; and (ii) Nrg1β1 or saline (control) were administered 1 h before each MPTP injection. We found that Nrg1β1 significantly reduced the loss of nigral dopaminergic neurons in both intoxication paradigms (7 days post-injection). However, Nrg1β1 did not reverse MPTP-induced decrease in dopamine levels and dopaminergic fibers in the striatum. We also show that MPTP conversion to its toxic metabolite 1-methyl-4-phenylpyridinium as well as levels of dopamine transporter, mediating intracellular uptake of 1-methyl-4-phenylpyridinium, are unaffected by Nrg1β1. Finally, neuroprotective properties of Nrg1β1 on nigral dopaminergic neurons are specifically mediated by ErbB4 as revealed through the study of ErbB4 knockout mice. In conclusion, systemically administered Nrg1β1 protects midbrain dopaminergic neurons against this PD-related toxic insult. Thus, Nrg1β1 may have a benefit in the treatment of PD patients. Previously, we demonstrated that systemically administered neuregulin-1β1 (Nrg1β1) passes the blood-brain barrier, phosphorylates ErbB4 receptors and elevates dopamine (DA) levels in the nigrostriatal system of healthy mice. Nrg1β1 protects nigral DAergic neurons in the 6-hydroxydopamine (6-OHDA) mouse model of Parkinson's disease (PD). Here, we show that Nrg1β1 rescues nigral DAergic neurons also against 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced cell death. ErbB4 expression is essential for the neuroprotective effect of Nrg1β1 on midbrain DAergic neurons. Nrg1β1 might be beneficial in PD treatment.

Genetic labeling reveals novel cellular targets of schizophrenia susceptibility gene: distribution of GABA and non-GABA ErbB4-positive cells in adult mouse brain

Neuregulin 1 (NRG1) and its receptor ErbB4 are schizophrenia risk genes. NRG1-ErbB4 signaling plays a critical role in neural development and regulates neurotransmission and synaptic plasticity. Nevertheless, its cellular targets remain controversial. ErbB4 was thought to express in excitatory neurons, although recent studies disputed this view. Using mice that express a fluorescent protein under the promoter of the ErbB4 gene, we determined in what cells ErbB4 is expressed and their identity. ErbB4 was widely expressed in the mouse brain, being highest in amygdala and cortex. Almost all ErbB4-positive cells were GABAergic in cortex, hippocampus, basal ganglia, and most of amygdala in neonatal and adult mice, suggesting GABAergic transmission as a major target of NRG1-ErbB4 signaling in these regions. Non-GABAergic, ErbB4-positive cells were present in thalamus, hypothalamus, midbrain, and hindbrain. In particular, ErbB4 is expressed in serotoninergic neurons of raphe nuclei but not in norepinephrinergic neurons of the locus ceruleus. In hypothalamus, ErbB4 is present in neurons that express oxytocin. Finally, ErbB4 is expressed in a group of cells in the subcortical areas that are positive for S100 calcium binding protein β. These results identify novel cellular targets of NRG1-ErbB4 signaling.

Perinatal asphyxia alters neuregulin-1 and COMT gene expression in the medial prefrontal cortex in rats

Epidemiological studies suggest that perinatal complications, particularly hypoxia-related ones, increase the risk of schizophrenia. Recent genetic studies of the disorder have identified several putative susceptibility genes, some of which are known to be regulated by hypoxia. It can be postulated therefore that birth complications that cause hypoxia in the fetal brain may be associated with a dysregulation in the expression of some of the schizophrenia candidate genes. To test this, we used an animal model of perinatal asphyxia, in which rat pups were exposed to 15 min of intrauterine anoxia during Caesarean section birth, and examined the expression of mRNA of five of the putative susceptibility genes (NRG1, ErbB4, AKT1, COMT and BDNF) by real-time quantitative PCR in the medial prefrontal cortex (mPFC) and the hippocampus at 6 and 12 weeks after birth. The expression of NRG1 mRNA was significantly decreased in the mPFC, but not in the hippocampus, at 6 and 12 weeks after birth. In addition, a significant increase in COMT mRNA expression was observed in the mPFC at 12 weeks. The alteration in mRNA levels of NRG1 and COMT was not associated with a change in their protein levels. These results suggest that perinatal asphyxia may lead to disturbances in the PFC, which in turn may exert a long-lasting influence on the expression of specific genes, such as NRG1 and COMT. Our results also suggest that translational interruption may occur in this model of perinatal asphyxia.

Disruption of the ErbB signaling in adolescence increases striatal dopamine levels and affects learning and hedonic-like behavior in the adult mouse

The ErbB signaling pathway has been genetically and functionally implicated in schizophrenia. Numerous findings support the dysregulation of Neuregulin (NRG) and epidermal growth factor (EGF) signaling in schizophrenia. However, it is unclear whether alterations of these pathways in the adult brain or during development are involved in the pathophysiology of schizophrenia. Herein we characterized the behavioral profile and molecular changes resulting from pharmacologically blocking the ErbB signaling pathway during a critical period in the development of decision making, planning, judgments, emotions, social cognition and cognitive skills, namely adolescence. We demonstrate that chronic administration of the pan-ErbB kinase inhibitor JNJ-28871063 (JNJ) to adolescent mice elevated striatal dopamine levels and reduced preference for sucrose without affecting locomotor activity and exploratory behavior. In adulthood, adolescent JNJ-treated mice continue to consume less sucrose and needed significantly more correct-response trials to reach the learning criterion during the discrimination phase of the T-maze reversal learning task than their saline-injected controls. In addition, JNJ mice exhibited deficit in reference memory but not in working memory as measured in the radial arm maze. Inhibition of the pathway during adolescence did not affect exploratory behavior and locomotor activity in the open field, social interaction, social memory, and reversal learning in adult mice. Our data suggest that alteration of ErbB signaling during adolescence resulted in changes in the dopaminergic systems that emerge in pathological learning and hedonic behavior in adulthood, and pinpoints the possible role of the pathway in the development of cognitive skills and motivated behavior.

Neuregulin-ERBB signaling in the nervous system and neuropsychiatric diseases

Neuregulins (NRGs) comprise a large family of growth factors that stimulate ERBB receptor tyrosine kinases. NRGs and their receptors, ERBBs, have been identified as susceptibility genes for diseases such as schizophrenia (SZ) and bipolar disorder. Recent studies have revealed complex Nrg/Erbb signaling networks that regulate the assembly of neural circuitry, myelination, neurotransmission, and synaptic plasticity. Evidence indicates there is an optimal level of NRG/ERBB signaling in the brain and deviation from it impairs brain functions. NRGs/ERBBs and downstream signaling pathways may provide therapeutic targets for specific neuropsychiatric symptoms.

Neuropathologic implication of peripheral neuregulin-1 and EGF signals in dopaminergic dysfunction and behavioral deficits relevant to schizophrenia: their target cells and time window

Neuregulin-1 and epidermal growth factor (EGF) are implicated in the pathogenesis of schizophrenia. To test the developmental hypothesis for schizophrenia, we administered these factors to rodent pups, juveniles, and adults and characterized neurobiological and behavioral consequences. These factors were also provided from their transgenes or infused into the adult brain. Here we summarize previous results from these experiments and discuss those from neuropathological aspects. In the neonatal stage but not the juvenile and adult stages, subcutaneously injected factors penetrated the blood-brain barrier and acted on brain neurons, which later resulted in persistent behavioral and dopaminergic impairments associated with schizophrenia. Neonatally EGF-treated animals exhibited persistent hyperdopaminergic abnormalities in the nigro-pallido-striatal system while neuregulin-1 treatment resulted in dopaminergic deficits in the corticolimbic dopamine system. Effects on GABAergic and glutamatergic systems were transient or limited. Even in the adult stage, intracerebral administration and transgenic expression of these factors produced similar but not identical behavioral impairments, although the effects of intracerebral administration were reversible. These findings suggest that dopaminergic development is highly vulnerable to circulating ErbB ligands in the pre- and perinatal stages. Once maldevelopment of the dopaminergic system is established during early development, dopamine-associating behavioral deficits become irreversible and manifest at postpubertal stages.

Distinct phenotypes of new transmembrane-domain neuregulin 1 mutant mice and the rescue effects of valproate on the observed schizophrenia-related cognitive deficits

Accumulating evidence suggests that neuregulin 1 (NRG1) might be involved in the neurodevelopment, neural plasticity, GABAergic neurotransmission, and pathogenesis of schizophrenia. NRG1 is abundantly expressed in the hippocampus, and emerging studies have begun to reveal the link between NRG1 signaling and cognitive deficits in schizophrenic patients. Because the transmembrane domain of NRG1 is vital for both forward and reverse signaling cascades, new Nrg1-deficient mice that carry a truncation of the transmembrane domain of the Nrg1 gene were characterized and used in this study to test a NRG1 loss-of-function hypothesis for schizophrenia. Both male and female Nrg1 heterozygous mutant mice and their wild-type littermates were used in a series of 4 experiments to characterize the impact of Nrg1 on behavioral phenotypes and to determine the importance of Nrg1 in the regulation of hippocampal neuromorphology and local GABAergic interneurons. First, a comprehensive battery of behavioral tasks indicated that male Nrg1-deficient mice exhibited significant impairments in cognitive functions. Second, pharmacological challenges were conducted and revealed that Nrg1 haploinsufficiency altered GABAergic activity in males. Third, although no genotype-specific neuromorphological alterations were found in the hippocampal CA1 pyramidal neurons, significant reductions in the hippocampal expressions of GAD67 and parvalbumin were revealed in the Nrg1-deficient males. Fourth, chronic treatment with valproate rescued the observed behavioral deficits and hippocampal GAD67 reduction in Nrg1-deficient males. Collectively, these results indicate the potential therapeutic effect of valproate and the importance of Nrg1 in the regulation of cognitive functions and hippocampal GABAergic interneurons, especially in males.

The role of EGFR and ErbB family related proteins in the oligodendrocyte specification in germinal niches of the adult mammalian brain

In the adult brain, multipotent progenitor cells have been identified in three areas: the ventricular-subventricular zone (VZ-SVZ), adjacent to the striatal wall of the lateral ventricles, the subgranular zone (SGZ), located at the dentate gyrus of the hippocampus and the subcallosal zone (SCZ), located between the corpus callosum and the CA1 and CA2 regions of the hippocampus. The neural progenitor cells of these regions express the epidermal growth factor receptor (EGFR, ErbB-1 or HER1). EGF, the most important ligand for the EGFR, is a potent mitogenic agent that stimulates proliferation, survival, migration and differentiation into the oligodendrocyte lineage. Other ErbB receptors also activate several intracellular pathways for oligodendrocyte specification, migration and survival. However, the specific downstream pathways related to oligodendrogenesis and the hierarchic interaction among intracellular signaling cascades is not well-known. We summarize the current data regarding the role of EGFR and ErbB family signaling on neural stem cells and the downstream cascades involved in oligodendrogenesis in the neurogenic niches of the adult brain. Understanding the mechanisms that regulate proliferation, differentiation, migration of oligodendrocytes and myelination is of critical importance for the field of neurobiology and constitutes a crucial step in the design of stem-cell-based therapies for demyelinating diseases.

LGR5 is a proneural factor and is regulated by OLIG2 in glioma stem-like cells

The biological functional roles of LGR5 (leucine-rich repeat containing G protein-coupled receptor 5, also known as GPR49), a novel potential marker for stem-like cells in glioblastoma (GSCs), is poorly acknowledged. Here, we demonstrated that LGR5 was detected in glioblastoma tissues and GSCs. Bioinformatics analysis revealed that LGR5 is closely related to neurogenesis and neuronal functions, and preferentially expressed in Proneural subtype of GBMs. Furthermore, LGR5 is regulated by Proneural factor OLIG2, which is important for both neurogenesis and GSC maintenance. Biological experiments in GSC cells validated the bioinformatics analysis results and revealed that LGR5 regulated the tumor sphere formation capacity, an important stem cell property for GSCs. Therefore, LGR5 expression may be functionally correlated with the neurogenic competence, and be regulated by OLIG2 in GSCs.

Diabetes and cognitive deficits in chronic schizophrenia: a case-control study

Cognitive impairment occurs in both schizophrenia and diabetes. There is currently limited understanding whether schizophrenia with diabetes has more serious cognitive deficits than schizophrenia without diabetes or diabetes only. This study assessed cognitive performance in 190 healthy controls, 106 diabetes only, 127 schizophrenia without diabetes and 55 schizophrenia with diabetes. This study was conducted from January 2008 to December 2010. Compared to healthy controls, all patient groups had significantly decreased total and five index RBANS scores (all p<0.01-p<0.001), except for the visuospatial/constructional index. Schizophrenia with diabetes performed worse than schizophrenia without diabetes in immediate memory (p<0.01) and total RBANS scores (<0.05), and showed a trend for decreased attention (p = 0.052) and visuospatial/constructional capacity (p = 0.063). Schizophrenia with diabetes performed worse than diabetes only in immediate memory (p<0.001) and attention (p<0.05), and showed a trend for decreased total RBANS scores (p = 0.069). Regression analysis showed that the RBANS had modest correlations with schizophrenia' PANSS scores, their duration of current antipsychotic treatment, and diagnosis of diabetes. Schizophrenia with co-morbid diabetes showed more cognitive impairment than schizophrenia without diabetes and diabetes only, especially in immediate memory and attention.

Neurobehavioral deficits of epidermal growth factor-overexpressing transgenic mice: impact on dopamine metabolism

Epidermal growth factor (EGF) and its family member neuregulin-1 are implicated in the etiology of schizophrenia. Our recent pharmacological studies indicate that EGF injections to neonatal and adult rats both induce neurobehavioral deficits relevant to schizophrenia. We, however, did not evaluate the genetic impact of EGF transgene on neurobehavioral traits. Here we analyzed transgenic mice carrying the transgene of mouse EGF cDNA. As compared to control littermates, heterozygous EGF transgenic mice had an increase in EGF mRNA levels and showed significant decreases in prepulse inhibition and context-dependent fear learning, but there were no changes in locomotor behaviors and sound startle responses. In addition, these transgenic mice exhibited higher behavioral sensitivity to the repeated cocaine injections. There were neurochemical alterations in metabolic enzymes of dopamine (i.e., tyrosine hydroxylase, dopa decarboxylase, catechol-O-methyl transferase) and monoamine contents in various brain regions of the EGF transgenic mice, but there were no apparent neuropathological signs in the brain. The present findings rule out the indirect influence of anti-EGF antibody production on the reported behavioral deficits of EGF-injected mice. These results support the argument that aberrant hyper-signals of EGF have significant impact on mouse behavioral traits and dopamine metabolism.

ErbB inhibitors ameliorate behavioral impairments of an animal model for schizophrenia: implication of their dopamine-modulatory actions

Ligands for ErbB receptors, including epidermal growth factor (EGF) and neuregulin-1, have a neurotrophic activity on midbrain dopaminergic neurons and are implicated in the pathophysiology of schizophrenia. Although ErbB kinase inhibitors ameliorate behavioral deficits of the schizophrenia model that was established by hippocampal lesioning of rat pups, the antipsychotic action of ErbB kinase inhibitors and its general applicability to other models are not fully characterized. Using a different animal model, here, we examined whether and how ErbB kinase inhibitors ameliorate the behavioral endophenotypes relevant to schizophrenia. The animal model for schizophrenia was prepared by exposing neonatal rats to the cytokine EGF. Intraventricular infusion of the ErbB1 inhibitors ZD1839 and PD153035 in these animals ameliorated the deficits in startle response and prepulse inhibition in a dose-dependent manner. The deficits of latent inhibition of fear learning were also alleviated by ZD1839 with its limited effects on body weight gain or locomotor activity. ZD1839 infusion also decreased the busting activity of nigral dopamine (DA) neurons and reduced pallidal DA metabolism, a result that mimics the anti-dopaminergic profile of risperidone and haloperidol in this brain region. ErbB inhibitors appear to have anti-dopaminergic actions to alleviate some of the behavioral deficits common to animal models for schizophrenia.

Essential roles of heparin-binding epidermal growth factor-like growth factor in the brain

Heparin-binding epidermal growth factor-like growth factor (HB-EGF) is a member of the EGF family of growth factors, which interacts with the EGF receptor to exert mitogenic activity for various types of cells. Through its interactions with various molecules, it is involved in diverse biological processes, including wound healing, blast implantation, and tumor formation. At the same time, HB-EGF is widely expressed in the central nervous system, including the hippocampus and cerebral cortex, and is considered to play pivotal roles in the developing and adult nervous system. Because HB-EGF protein levels in the brain are much higher than those of TGF-α and EGF, it is possible that HB-EGF serves as a major physiologic ligand for the EGF receptor (ErbB1) within the central nervous system. Recent studies indicate that HB-EGF contributes to the neuronal survival and proliferation of glial/stem cells. HB-EGF also promotes the survival of dopaminergic neurons, an action mediated by mitogen-activated protein kinase (MAPK) as well as by the Akt signaling pathway. In this review, we discuss recent findings on the implications of HB-EGF in higher brain functions of the central nervous system.

Neuregulin-1 signalling and antipsychotic treatment: potential therapeutic targets in a schizophrenia candidate signalling pathway

Identifying the signalling pathways underlying the pathophysiology of schizophrenia is an essential step in the rational development of new antipsychotic drugs for this devastating disease. Evidence from genetic, transgenic and post-mortem studies have strongly supported neuregulin-1 (NRG1)-ErbB4 signalling as a schizophrenia susceptibility pathway. NRG1-ErbB4 signalling plays crucial roles in regulating neurodevelopment and neurotransmission, with implications for the pathophysiology of schizophrenia. Post-mortem studies have demonstrated altered NRG1-ErbB4 signalling in the brain of schizophrenia patients. Antipsychotic drugs have different effects on NRG1-ErbB4 signalling depending on treatment duration. Abnormal behaviours relevant to certain features of schizophrenia are displayed in NRG1/ErbB4 knockout mice or those with NRG1/ErbB4 over-expression, some of these abnormalities can be improved by antipsychotic treatment. NRG1-ErbB4 signalling has extensive interactions with the GABAergic, glutamatergic and dopaminergic neurotransmission systems that are involved in the pathophysiology of schizophrenia. These interactions provide a number of targets for the development of new antipsychotic drugs. Furthermore, the key interaction points between NRG1-ErbB4 signalling and other schizophrenia susceptibility genes may also potentially provide specific targets for new antipsychotic drugs. In general, identification of these targets in NRG1-ErbB4 signalling and interacting pathways will provide unique opportunities for the development of new generation antipsychotics with specific efficacy and fewer side effects.

What does a mouse tell us about neuregulin 1-cannabis interactions?

The link between cannabis and psychosis has been debated although there is substantial epidemiological evidence showing that cannabis increases the risk of psychosis. It has been hypothesized that schizophrenia patients carrying particular risk genes might be more sensitive to the psychosis-inducing effects of cannabis than other patients and healthy test subjects. Here we review the effects of cannabinoids on a mutant mouse model for the schizophrenia candidate gene neuregulin 1 (Nrg1). The studies suggest a complex interaction between cannabis and Nrg1: the neuro-behavioral effects of cannabinoids were different in Nrg1 mutant and control mice and depended on exposure time, sex, and age of test animals. This research provides the first evidence of complex cannabis-Nrg1 interactions suggesting Nrg1 as a prime target for future clinical investigations. Furthermore, it highlights that animal model research can broaden our understanding of the complex multi-factorial etiology of schizophrenia. Finally, the findings are important to preventive psychiatry: if the genes that confer genetic vulnerability to cannabis-induced psychosis were identified patients at-high risk could be forewarned of the potential dangers of cannabis abuse.

ErbB1-4-dependent EGF/neuregulin signals and their cross talk in the central nervous system: pathological implications in schizophrenia and Parkinson's disease

Ligands for ErbB1-4 receptor tyrosine kinases, such as epidermal growth factor (EGF) and neuregulins, regulate brain development and function. Thus, abnormalities in their signaling are implicated in the etiology or pathology of schizophrenia and Parkinson's disease. Among the ErbB receptors, ErbB1, and ErbB4 are expressed in dopamine and GABA neurons, while ErbB1, 2, and/or 3 are mainly present in oligodendrocytes, astrocytes, and their precursors. Thus, deficits in ErbB signaling might contribute to the neurological and psychiatric diseases stemming from these cell types. By incorporating the latest cancer molecular biology as well as our recent progress, we discuss signal cross talk between the ErbB1-4 subunits and their neurobiological functions in each cell type. The potential contribution of virus-derived cytokines (virokines) that mimic EGF and neuregulin-1 in brain diseases are also discussed.