Persistent NRG1 Type III Overexpression in Spinal Motor Neurons Has No Therapeutic Effect on ALS-Related Pathology in SOD1G93A Mice

Amyotrophic lateral sclerosis (ALS) is a devastating neurodegenerative disease affecting upper and lower motor neurons (MNs). Neuregulin-1 (NRG1) is a pleiotropic growth factor that has been shown to be potentially valuable for ALS when supplemented by means of viral-mediated gene therapy. However, these results are inconsistent with other reports. An alternative approach for investigating the therapeutic impact of NRG1 on ALS is the use of transgenic mouse lines with genetically defined NRG1 overexpression. Here, we took advantage of a mouse line with NRG1 type III overexpression in spinal cord α motor neurons (MN) to determine the impact of steadily enhanced NRG1 signalling on mutant superoxide dismutase 1 (SOD1)-induced disease. The phenotype of SOD1G93A-NRG1 double transgenic mice was analysed in detail, including neuropathology and extensive behavioural testing. At least 3 animals per condition and sex were histopathologically assessed, and a minimum of 10 mice per condition and sex were clinically evaluated. The accumulation of misfolded SOD1 (mfSOD1), MN degeneration, and a glia-mediated neuroinflammatory response are pathological hallmarks of ALS progression in SOD1G93A mice. None of these aspects was significantly improved when examined in double transgenic NRG1-SOD1G93A mice. In addition, behavioural testing revealed that NRG1 type III overexpression did not affect the survival of SOD1G93A mice but accelerated disease onset and worsened the motor phenotype.

Neuregulin-1 attenuates hemolysis- and ischemia induced-cerebrovascular inflammation associated with sickle cell disease

OBJECTIVES

Individuals with sickle cell disease (SCD) are at severely heightened risk for cerebrovascular injury and acute cerebrovascular events, including ischemic and hemorrhagic stroke, potentially leading to impaired development and life-long physical and cognitive disabilities. Cerebrovascular injury specific to SCD includes inflammation caused by underlying conditions of chronic hemolysis and reduced cerebrovascular perfusion. The objectives of this study were to investigate whether expression of neuregulin-1β (NRG-1), an endogenous neuroprotective polypeptide, is increased in SCD or experimental conditions mimicking the hemolysis and ischemic conditions of SCD, and to determine if treatment with exogenous NRG-1 reduces markers of cerebrovascular inflammation.

MATERIALS AND METHODS

Plasma and brain-specific NRG-1 levels were measured in transgenic SCD mice. Endogenous NRG-1 levels and response to experimental conditions of excess heme and ischemia were measured in cultured human brain microvascular cells and astrocytes. Pre-treatment with NRG-1 was used to determine NRG-1's ability to ameliorate resultant cerebrovascular inflammation.

RESULTS

Plasma and brain-specific NRG-1 were elevated in transgenic SCD mice compared to healthy controls. Neuregulin-1 expression was significantly increased in cultured human microvascular cells and astrocytes exposed to excess heme and ischemia. Pre-treatment with NRG-1 reduced inflammatory chemokine (CXCL-1 and CXCL-10) and adhesion molecule (ICAM-1 and VCAM-1) expression and increased pro-angiogenic factors (VEGF-A) in microvascular cells and astrocytes exposed to excess heme and ischemia.

CONCLUSIONS

Elevated NRG-1 in SCD is likely a protective endogenous response to ongoing cerebrovascular insults caused by chronic hemolysis and reduced cerebrovascular perfusion. Administration of NRG-1 to reduce cerebrovascular inflammation may be therapeutically beneficial in SCD and warrants continued investigation.

Neuregulin modulates hormone receptor levels in breast cancer through concerted action on multiple signaling pathways

The Neuregulins (NRGs) are growth factors that bind and activate ErbB/HER receptor tyrosine kinases. Some reports have described an interplay between this ligand-receptor system and hormonal receptors in breast cancer. However, the mechanisms by which NRGs regulate hormonal receptor signaling have not been sufficiently described. Here, we show that in breast cancer cells the activation of NRG receptors down-regulated ERα through a double mechanism that included post-transcriptional and transcriptional effects. This regulation required the concerted participation of three signaling routes: the PI3K/AKT/mTOR, ERK1/2, and ERK5 pathways. Moreover, these three routes were also involved in the phosphorylation of ERα at serines 118 and 167, two residues implicated in resistance to endocrine therapies. On the other hand, NRGs conferred resistance to fulvestrant in breast cancer cells and this resistance could be reversed when the three pathways activated by NRGs were simultaneously inhibited. Our results indicate that estrogen receptor-positive (ER+) breast tumors that can have access to NRGs may be resistant to fulvestrant. This resistance could be overcome if strategies to target the three main pathways involved in the interplay between NRG receptors and ERα could be developed.

Nucleolar localization of the ErbB3 receptor as a new target in glioblastoma

Background

The nucleolus is a subnuclear, non-membrane bound domain that is the hub of ribosome biogenesis and a critical regulator of cell homeostasis. Rapid growth and division of cells in tumors are correlated with intensive nucleolar metabolism as a response to oncogenic factors overexpression. Several members of the Epidermal Growth Factor Receptor (EGFR) family, have been identified in the nucleus and nucleolus of many cancer cells, but their function in these compartments remains unexplored.

Results

We focused our research on the nucleolar function that a specific member of EGFR family, the ErbB3 receptor, plays in glioblastoma, a tumor without effective therapies. Here, Neuregulin 1 mediated proliferative stimuli, promotes ErbB3 relocalization from the nucleolus to the cytoplasm and increases pre-rRNA synthesis. Instead ErbB3 silencing or nucleolar stress reduce cell proliferation and affect cell cycle progression.

Conclusions

These data point to the existence of an ErbB3-mediated non canonical pathway that glioblastoma cells use to control ribosomes synthesis and cell proliferation. These results highlight the potential role for the nucleolar ErbB3 receptor, as a new target in glioblastoma.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12860-022-00411-y.

Timing of maternal immune activation and sex influence schizophrenia-relevant cognitive constructs and neuregulin and GABAergic pathways

Maternal immune activation (MIA) during pregnancy is an established environmental risk factor for schizophrenia. Timing of immune activation exposure as well as sex of the exposed offspring are critical factors in defining the effects of MIA. However, the specificity of MIA on the component structure of schizophrenia, especially cognition, has been difficult to assess due to a lack of translational validity of maze-like testing paradigms. We aimed to assess cognitive domains relevant to schizophrenia using highly translational touchscreen-based tasks in male and female mice exposed to the viral mimetic, poly(I:C) (5 mg/k, i.p.), during early (gestational day (GD) 9-11) and late (GD13-15) gestational time points. Gene expression of schizophrenia candidate pathways were assessed in fetal brain immediately following poly(I:C) exposure and in adulthood to identify its influence on neurodevelopmental processes. Sex and window specific alterations in cognitive performance were found with the early window of MIA exposure causing female-specific disruptions to working memory and reduced perseverative behaviour, while late MIA exposure caused male-specific changes to working memory and deficits in reversal learning. GABAergic specification marker, Nkx2.1 gene expression was reduced in fetal brains and reelin expression was reduced in adult hippocampus of both early and late poly(I:C) exposed mice. Neuregulin and EGF signalling were initially upregulated in the fetal brain, but were reduced in the adult hippocampus, with male mice exposed in the late window showing reduced Nrg3 expression. Serine racemase was reduced in both fetal and adult brain, but again, adult reductions were specific to male mice exposed at the late time point. Overall, we show that cognitive constructs relevant to schizophrenia are altered by in utero exposure to maternal immune activation, but are highly dependent on the timing of infection and the sex of the offspring. Glutamatergic and epidermal growth factor pathways were similarly altered by MIA in a timing and sex dependent manner, while MIA-induced GABAergic deficits were independent of timing or sex.

Differential Methylation Pattern of Schizophrenia Candidate Genes in Tetrahydrocannabinol-Consuming Treatment-Resistant Schizophrenic Patients Compared to Non-Consumer Patients and Healthy Controls

BACKGROUND

Patients suffering from schizophrenic psychosis show reduced synaptic connectivity compared to healthy individuals. Furthermore, the use of cannabis often precedes the onset of schizophrenic psychosis. Therefore, we investigated whether consumption of cannabis has an impact on the methylation pattern of schizophrenia candidate genes concerned with the development and preservation of synapses and synaptic function.

METHODS

Fifty blood samples of outpatients affected by treatment-resistant schizophrenic psychosis were collected in the outpatient department of Ch Ste Anne/INSERM (Paris, France). Extracted DNA was sent to the LMN/MHH (Hanover, Germany) where DNA samples were bisulfite converted. The methylation patterns of the promoter region of neuregulin 1 (NRG1), neurexin (NRXN1), disrupted in schizophrenia 1 (DISC1), and microtubule-associated-protein tau (MAPT) were then analysed by sequencing according to Sanger.

RESULTS

In NRXN1 the group of non-consumer patients showed a methylation rate slightly lower than controls. In patients with preliminary use of tetrahydrocannabinol (THC) the NRXN1 promoter turned out to be methylated almost two times higher than in non-consumer patients. In MAPT, non-consumer patients showed a significant lower mean methylation rate in comparison to controls. In THC-consuming patients the difference compared with controls became less. NRG1 and DISC1 showed no significant differences between groups, whereas DISC1 appeared to be not methylated at all.

CONCLUSION

In MAPT and NRXN1 mean methylation rates were lower in non-consumer patients compared with controls, which seems to be a compensatory mechanism. With consumption of THC, mean methylation rates were increased: in the case of MAPT compared with controls, and in NRXN1 even significantly beyond that. Methylation of NRG1 and DISC1 seems not to be affected by the psychiatric disorder or by consumption of THC.

Prrx1b restricts fibrosis and promotes Nrg1-dependent cardiomyocyte proliferation during zebrafish heart regeneration

Fibroblasts are activated to repair the heart following injury. Fibroblast activation in the mammalian heart leads to a permanent fibrotic scar that impairs cardiac function. In other organisms, such as zebrafish, cardiac injury is followed by transient fibrosis and scar-free regeneration. The mechanisms that drive scarring versus scar-free regeneration are not well understood. Here, we show that the homeobox-containing transcription factor Prrx1b is required for scar-free regeneration of the zebrafish heart as the loss of Prrx1b results in excessive fibrosis and impaired cardiomyocyte proliferation. Through lineage tracing and single-cell RNA sequencing, we find that Prrx1b is activated in epicardial-derived cells where it restricts TGFβ ligand expression and collagen production. Furthermore, through combined in vitro experiments in human fetal epicardial-derived cells and in vivo rescue experiments in zebrafish, we conclude that Prrx1 stimulates Nrg1 expression and promotes cardiomyocyte proliferation. Collectively, these results indicate that Prrx1 is a key transcription factor that balances fibrosis and regeneration in the injured zebrafish heart. This article has an associated 'The people behind the papers' interview.

Lessons from Injury: How Nerve Injury Studies Reveal Basic Biological Mechanisms and Therapeutic Opportunities for Peripheral Nerve Diseases

Since Waller and Cajal in the nineteenth and early twentieth centuries, laboratory traumatic peripheral nerve injury studies have provided great insight into cellular and molecular mechanisms governing axon degeneration and the responses of Schwann cells, the major glial cell type of peripheral nerves. It is now evident that pathways underlying injury-induced axon degeneration and the Schwann cell injury-specific state, the repair Schwann cell, are relevant to many inherited and acquired disorders of peripheral nerves. This review provides a timely update on the molecular understanding of axon degeneration and formation of the repair Schwann cell. We discuss how nicotinamide mononucleotide adenylyltransferase 2 (NMNAT2) and sterile alpha TIR motif containing protein 1 (SARM1) are required for axon survival and degeneration, respectively, how transcription factor c-JUN is essential for the Schwann cell response to nerve injury and what each tells us about disease mechanisms and potential therapies. Human genetic association with NMNAT2 and SARM1 strongly suggests aberrant activation of programmed axon death in polyneuropathies and motor neuron disorders, respectively, and animal studies suggest wider involvement including in chemotherapy-induced and diabetic neuropathies. In repair Schwann cells, cJUN is aberrantly expressed in a wide variety of human acquired and inherited neuropathies. Animal models suggest it limits axon loss in both genetic and traumatic neuropathies, whereas in contrast, Schwann cell secreted Neuregulin-1 type 1 drives onion bulb pathology in CMT1A. Finally, we discuss opportunities for drug-based and gene therapies to prevent axon loss or manipulate the repair Schwann cell state to treat acquired and inherited neuropathies and neuronopathies.

Neuroprotective effect of neuregulin-1β on spinal cord ischemia reperfusion injury

Objective: This study was designed to see if neuregulin-1β (NRG-1β) plays a protective role in spinal cord ischemia and reperfusion injury (SCII).Design: Animal research.Setting: China.Participants: NA.Interventions: Forty-eight SD rats were randomly divided into control group (n = 16), SCII model group (n = 16) and NRG-1β-treated group (n = 16). In control group, the abdominal aorta was isolated but not clipped. The rats in NRG-1β-treated group were treated with 10μg/kg NRG-1β during developing SCII model.Outcome Measures: Neurological scores were evaluated. At 3, 6, 12 and 24 h after the reperfusion, rats were killed. Pathological changes of spinal cord were assessed with HE staining, and immunohistochemical staining of matrix metalloproteinases-9 (MMP-9) and tissue inhibitor of metalloproteinase-1 (TIMP-1). MMP-9 and TIMP-1 mRNA levels were assessed using real-time PCR.Results: NRG-1β reduced the damage of SCII in the rats. The expression of MMP-9 protein and mRNA in NRG-1β treatment group was significantly lower than the model group (P < 0.05) at 6 h, 12 h and 24 h after the perfusion. The expression of TIMP-1 protein and mRNA in the treatment group was significantly higher than the model group at 12 h and 24 h after the perfusion.Conclusion: NRG-1β reduced the reperfusion damage in rat model of SCII, in which process MMP-9 and TIMP-1 were probably involved.

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

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

NRG1 fusions: Biology to therapy

NRG1 fusions are rare oncogenic drivers that exist at low frequencies across multiple tumor types. They are uncommon in lung cancer with an estimated incidence of 0.2 %. NRG1 fusions have a unique biology and are challenging to detect, due to large intronic regions of the gene, but they do represent possible therapeutic targets. Several agents targeting the ErbB signaling pathway have shown early evidence of efficacy including pan-ErbB kinase inhibitors, monoclonal antibodies, and bispecific antibodies. Supporting data are limited to case reports and small series for now, but prospective trials are underway. While our understanding of these fusions is still evolving, it is clear that NRG1 will be a clinically relevant finding in the years to come.

Human blood serum can donor-specifically antagonize effects of EGFR-targeted drugs on squamous carcinoma cell growth

Many patients fail to respond to EGFR-targeted therapeutics, and personalized diagnostics is needed to identify putative responders. We investigated 1630 colorectal and lung squamous carcinomas and 1357 normal lung and colon samples and observed huge variation in EGFR pathway activation in both cancerous and healthy tissues, irrespectively on EGFR gene mutation status. We investigated whether human blood serum can affect squamous carcinoma cell growth and EGFR drug response. We demonstrate that human serum antagonizes the effects of EGFR-targeted drugs erlotinib and cetuximab on A431 squamous carcinoma cells by increasing IC50 by about 2- and 20-fold, respectively. The effects on clonogenicity varied significantly across the individual serum samples in every experiment, with up to 100% differences. EGF concentration could explain many effects of blood serum samples, and EGFR ligands-depleted serum showed lesser effect on drug sensitivity.

EGFR-targeting antitumor therapy: Neuregulins or antibodies?

Malignancies such as lung, breast and pancreatic carcinomas are associated with increased expression of the epidermal growth factor receptor, EGFR, and its role in the pathogenesis and progression of tumors has made this receptor a prime target in the development of antitumor therapies. In therapies targeting EGFR, the development of resistance owing to mutations and single nucleotide polymorphisms, and the expression of the receptor ligands themselves are very serious issues. In this work, both the ligand neuregulin and a bispecific antibody fragment to EGFR are conjugated separately or together to the same drug-delivery system to find the most promising candidate. Camptothecin is used as a model chemotherapeutic drug and superparamagnetic iron oxide nanoparticles as a delivery system. Results show that the lowest LD50 is achieved by formulations conjugated to both the antibody and the ligand, demonstrating a synergy. Additionally, the ligand location in the nucleus favors the antitumor activity of Camptothecin. The high loading capacity and efficiency convert these systems into a good alternative for administering Camptothecin, a drug whose use is otherwise severely limited by its chemical instability and poor solubility. Our choice of targeting agents allows treating tumors that express ErbB2 (Her2+ tumors) as well as Her2- tumors expressing EGFR.

PDCD4 limits prooncogenic neuregulin-ErbB signaling

The neuregulins and their ErbB/HER receptors play essential roles in mammalian development and tissue homeostasis. In addition, deregulation of their function has been linked to the pathogenesis of diseases such as cancer or schizophrenia. These circumstances have stimulated research into the biology of this ligand-receptor system. Here we show the identification of programmed cell death protein-4 (PDCD4) as a novel neuregulin-ErbB signaling mediator. Phosphoproteomic analyses identified PDCD4 as protein whose phosphorylation increased in cells treated with neuregulin. Mutagenesis experiments defined serine 67 of PDCD4 as a site whose phosphorylation increased upon activation of neuregulin receptors. Phosphorylation of that site promoted degradation of PDCD4 by the proteasome, which depended on exit of PDCD4 from the nucleus to the cytosol. Mechanistic studies defined mTORC1 and ERK1/2 as routes implicated in neuregulin-induced serine 67 phosphorylation and PDCD4 degradation. Functionally, PDCD4 regulated several important biological functions of neuregulin, such as proliferation, migration, or invasion.

Growth factor therapy for cardiac repair: an overview of recent advances and future directions

Heart disease represents a significant public health burden and is associated with considerable morbidity and mortality at the level of the individual. Current therapies for pathologies such as myocardial infarction, cardiomyopathy and heart failure are unable to repair damaged tissue to an extent that provides restoration of function approaching that of the pre-diseased state. Novel approaches to repair and regenerate the injured heart include cell therapy and the use of exogenous factors. Improved understanding of the role of growth factors in endogenous cardiac repair processes has motivated the investigation of their potential as therapeutic agents for cardiac pathology. Despite the disappointing performance of other growth factors in historical clinical trials, insulin-like growth factor 1 (IGF-1), neuregulin and platelet-derived growth factor (PDGF) have recently emerged as new candidate therapies. These growth factors elicit tissue repair through anti-apoptotic, pro-angiogenic and fibrosis-modulating mechanisms and have produced clinically significant functional improvement in preclinical studies. Early human trials suggest that IGF-1 and neuregulin are well tolerated and yield dose-dependent benefit, warranting progression to later phase studies. However, outstanding challenges such as short growth factor serum half-life and insufficient target-organ specificity currently necessitate the development of novel delivery strategies.

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.

Neuregulin-1 triggers GLUT4 translocation and enhances glucose uptake independently of insulin receptor substrate and ErbB3 in neonatal rat cardiomyocytes

During stress conditions such as pressure overload and acute ischemia, the myocardial endothelium releases neuregulin-1β (NRG-1), which acts as a cardioprotective factor and supports recovery of the heart. Recently, we demonstrated that recombinant human (rh)NRG-1 enhances glucose uptake in neonatal rat ventricular myocytes via the ErbB2/ErbB4 heterodimer and PI3Kα. The present study aimed to further elucidate the mechanism whereby rhNRG-1 activates glucose uptake in comparison to the well-established insulin and to extend the findings to adult models. Combinations of rhNRG-1 with increasing doses of insulin did not yield any additive effect on glucose uptake measured as ³H-deoxy-d-glucose incorporation, indicating that the mechanisms of the two stimuli are similar. In c-Myc-GLUT4-mCherry-transfected neonatal rat cardiomyocytes, rhNRG-1 increased sarcolemmal GLUT4 by 16-fold, similar to insulin. In contrast to insulin, rhNRG-1 did not phosphorylate IRS-1 at Tyr⁶¹², indicating that IRS-1 is not implicated in the signal transmission. Treatment of neonatal rats with rhNRG-1 induced a signaling response comparable with that observed in vitro, including increased ErbB4-pTyr¹²⁸⁴, Akt-pThr³⁰⁸ and Erk1/2-pThr²⁰²/Tyr²⁰⁴. In contrast, in adult cardiomyocytes rhNRG-1 only increased the phosphorylation of Erk1/2 without having any significant effect on Akt and AS160 phosphorylation and glucose uptake, suggesting that rhNRG-1 function in neonatal cardiomyocytes differs from that in adult cardiomyocytes. In conclusion, our results show that similar to insulin, rhNRG-1 can induce glucose uptake by activating the PI3Kα-Akt-AS160 pathway and GLUT4 translocation. Unlike insulin, the rhNRG-1-induced effect is not mediated by IRS proteins and is observed in neonatal, but not in adult rat cardiomyocytes.

The influence of immune activation at early vs late gestation on fetal NRG1-ErbB4 expression and behavior in juvenile and adult mice offspring

Maternal inflammation during pregnancy is associated with a higher incidence of mental disorders (e.g. schizophrenia and autism) in the offspring. In our study, we investigate the involvement of the NRG-ErbB signaling pathway in rodent fetal brains four hours following maternal immune activation (MIA) insult at two different gestational days (i.e. early vs late). Furthermore, we test the long-term behavioral alteration of the exposed MIA mice at juvenile and adulthood. We demonstrate that MIA at late, but not at early gestation day, altered the expression of NRG1, its receptor ErbB4, and the dopamine D2 receptor four hours post injection of viral or bacterial mimic material in fetal brain. At the behavioral levels, adult late-MIA-exposed female offspring, but not juvenile, display lack preference to a novel object. While working memory alteration observed only in adult male MIA-exposed offspring at late gestation day. In addition, we found that adult females MIA-exposed mice spent more time in the center of the open field than female-saline groups. On the other hand, juvenile male offspring exposed to MIA at early, but not late, gestation day displayed a significant alteration in social interaction. Our results suggest that MIA during late gestation immediately influences the expression levels of the NRG1 and ErbB4 genes, and affects long-term behavioral changes at adulthood. These behavioral changes are time related and sex-specific. Thus, immune activation at late stages of the embryonic brain development initiates the activation of the NRG1-ErbB4 pathway and this disturbance might result in cognitive dysfunction in adulthood.

Impact of the Neuregulin rs35753505 C/T Polymorphisms on Neuregulin 1 Levels in Preterm Infants

BACKGROUND:

Neuregulin (NRG) 1 plays an important role in the development of various organ systems in human. Single nucleotide polymorphisms rs35753505 C/Tof the gene encoding NRG1 evident as allele C and T with genotypes of CT, CC, and TT are believed to have an impact on NRG1 levels.

AIM:

To determine the impact of the NRGrs35753505 C/T polymorphisms on NRG1 levels in preterm infants.

METHODS:

A cross-sectional study was conducted from February to December 2018, whereas 48 eligible preterm infants with a gestational age of 32- < 37 weeks were enrolled. An umbilical cord blood specimen was collected for determination of NRG1 levels with enzyme-linked immunosorbent assay (ELISA) and NRG1 polymorphisms with polymerase chain reaction (PCR). Statistical analysis was performed with 95%CI and P value of < 0.05 was considered statistically significant.

RESULTS:

Median value of NRG1 levels (174.4 pg/ml) served as a cut off value. NRG 1 polymorphisms composed distribution of CC (31%), CT (42%), TT (27%) genotypes and distribution of C and T alleles were 52% and 48%. The median NRG1 levels in CC and CT genotypes were significantly lower compared to TT genotype (151.1 pg/ml vs 407.2 pg/ml, P = 0.005 and 159.1 pg/ml vs 407.2 pg/ml, P = 0.009). Subjects with C allele had significantly lower median NRG1 levels than T allele (151.1 pg/ml vs 407.2 pg/ml, P = 0.002). Subjects with CC and CT genotypes had higher risk to develop lower NRG1 levels compared to TT genotype (OR = 8.25, P = 0.016 and OR = 10.74, P = 0.005, respectively).

CONCLUSION:

Allele C is associated with lower NRG1 levels. Preterm infants with CC and CT genotypes pose a higher risk to have lower NRG1 levels.

NMDA Receptors Regulate Neuregulin 2 Binding to ER-PM Junctions and Ectodomain Release by ADAM10 [corrected]

Unprocessed pro-neuregulin 2 (pro-NRG2) accumulates on neuronal cell bodies at junctions between the endoplasmic reticulum and plasma membrane (ER-PM junctions). NMDA receptors (NMDARs) trigger NRG2 ectodomain shedding from these sites followed by activation of ErbB4 receptor tyrosine kinases, and ErbB4 signaling cell-autonomously downregulates intrinsic excitability of GABAergic interneurons by reducing voltage-gated sodium channel currents. NMDARs also promote dispersal of Kv2.1 clusters from ER-PM junctions and cause a hyperpolarizing shift in its voltage-dependent channel activation, suggesting that NRG2/ErbB4 and Kv2.1 work together to regulate intrinsic interneuron excitability in an activity-dependent manner. Here we explored the cellular processes underlying NMDAR-dependent NRG2 shedding in cultured rat hippocampal neurons. We report that NMDARs control shedding by two separate but converging mechanisms. First, NMDA treatment disrupts binding of pro-NRG2 to ER-PM junctions by post-translationally modifying conserved Ser/Thr residues in its intracellular domain. Second, using a mutant NRG2 protein that cannot be modified at these residues and that fails to accumulate at ER-PM junctions, we demonstrate that NMDARs also directly promote NRG2 shedding by ADAM-type metalloproteinases. Using pharmacological and shRNA-mediated knockdown, and metalloproteinase overexpression, we unexpectedly find that ADAM10, but not ADAM17/TACE, is the major NRG2 sheddase acting downstream of NMDAR activation. Together, these findings reveal how NMDARs exert tight control over the NRG2/ErbB4 signaling pathway, and suggest that NRG2 and Kv2.1 are co-regulated components of a shared pathway that responds to elevated extracellular glutamate levels.

BMP4 and Neuregulin regulate the direction of mouse neural crest cell differentiation

The neural crest is a transient embryonic tissue that initially generates neural crest stem cells, which then migrate throughout the body to give rise to a variety of mature tissues. It was proposed that the fate of neural crest cells is gradually determined via environmental cues from the surrounding tissues. In the present study, neural crest cells were isolated and identified from mouse embryos. Bone morphogenetic protein 4 (BMP4) and Neuregulin (NRG) were employed to induce the differentiation of neural crest cells. Treatment with BMP4 revealed neuron-associated differentiation; cells treated with NRG exhibited differentiation into the Schwann cell lineage, a type of glia. Soft agar clonogenic and neurosphere formation assays were conducted to investigate the effects of N-Myc (MYCN) overexpression in neural crest cells; the number of colonies and neurospheres notably increased after 14 days. These findings demonstrated that the direction of cell differentiation may be affected by altering the factors present in the surrounding environment. In addition, MYCN may serve a key role in regulating neural crest cell differentiation.

Alzheimer's associated amyloid and tau deposition co-localizes with a homeostatic myelin repair pathway in two mouse models of post-stroke mixed dementia

The goal of this study was to determine the chronic impact of stroke on the manifestation of Alzheimer’s disease (AD) related pathology and behavioral impairments in mice. To accomplish this goal, we used two distinct models. First, we experimentally induced ischemic stroke in aged wildtype (wt) C57BL/6 mice to determine if stroke leads to the manifestation of AD-associated pathological β-amyloid (Aβ) and tau in aged versus young adult wt mice. Second, we utilized a transgenic (Tg) mouse model of AD (hAPP-SL) to determine if stroke leads to the worsening of pre-existing AD pathology, as well as the development of pathology in brain regions not typically expressed in AD Tg mice. In the wt mice, there was delayed motor recovery and an accelerated development of cognitive deficits in aged mice compared to young adult mice following stroke. This corresponded with increased brain atrophy, increased cholinergic degeneration, and a focal increase of Aβ in areas of axonal degeneration in the ipsilateral hemisphere of the aged animals. By contrast, in the hAPP-SL mice, we found that ischemia induced aggravated behavioral deficits in conjunction with a global increase in Aβ_, tau, and cholinergic pathology compared to hAPP-SL mice that underwent a sham stroke procedure. With regard to a potential mechanism, in both models, we found that the stroke-induced Aβ and tau deposits co-localized with increased levels of β-secretase 1 (BACE1), along with its substrate, neuregulin 1 (NGR1) type III, both of which are proteins integral for myelin repair. Based on these findings, we propose that the chronic sequelae of stroke may be ratcheting-up a myelin repair pathway, and that the consequent increase in BACE1 could be causing an inadvertent cleavage of its alternative substrate, AβPP, resulting in greater Aβ seeding and pathogenesis.

A Novel Ultrasensitive In Situ Hybridization Approach to Detect Short Sequences and Splice Variants with Cellular Resolution

Investigating the expression of RNAs that differ by short or single nucleotide sequences at a single-cell level in tissue has been limited by the sensitivity and specificity of in situ hybridization (ISH) techniques. Detection of short isoform-specific sequences requires RNA isolation for PCR analysis-an approach that loses the regional and cell-type-specific distribution of isoforms. Having the capability to distinguish the differential expression of RNA variants in tissue is critical because alterations in mRNA splicing and editing, as well as coding single nucleotide polymorphisms, have been associated with numerous cancers, neurological and psychiatric disorders. Here we introduce a novel highly sensitive single-probe colorimetric/fluorescent ISH approach that targets short exon/exon RNA splice junctions using single-pair oligonucleotide probes (~ 50 bp). We use this approach to investigate, with single-cell resolution, the expression of four transcripts encoding the neuregulin (NRG) receptor ErbB4 that differ by alternative splicing of exons encoding two juxtamembrane (JMa/JMb) and two cytoplasmic (CYT-1/CYT-2) domains that alter receptor stability and signaling modes, respectively. By comparing ErbB4 hybridization on sections from wild-type and ErbB4 knockout mice (missing exon 2), we initially demonstrate that single-pair probes provide the sensitivity and specificity to visualize and quantify the differential expression of ErbB4 isoforms. Using cell-type-specific GFP reporter mice, we go on to demonstrate that expression of ErbB4 isoforms differs between neurons and oligodendrocytes, and that this differential expression of ErbB4 isoforms is evolutionarily conserved to humans. This single-pair probe ISH approach, known as BaseScope, could serve as an invaluable diagnostic tool to detect alternative spliced isoforms, and potentially single base polymorphisms, associated with disease.

Re-Defining Stem Cell-Cardiomyocyte Interactions: Focusing on the Paracrine Effector Approach

Stem cell research for treating or curing ischemic heart disease has, till date, culminated in three basic approaches: the use of induced pluripotent stem cell (iPSC) technology; reprogramming cardiac fibroblasts; and cardiovascular progenitor cell regeneration. As each approach has been shown to have its advantages and disadvantages, exploiting the advantages while minimizing the disadvantages has been a challenge. Using human germline pluripotent stem cells (hgPSCs) along with a modified version of a relatively novel cell-expansion culture methodology to induce quick, indefinite expansion of normally slow growing hgPSCs, it was possible to emphasize the advantages of all three approaches. We consistently found that unipotent germline stem cells, when removed from their niche and cultured in the correct medium, expressed endogenously, pluripotency genes, which induced them to become hgPSCs. These cells are then capable of producing cell types from all three germ layers. Upon differentiation into cardiac lineages, our data consistently showed that they not only expressed cardiac genes, but also expressed cardiac-promoting paracrine factors. Taking these data a step further, we found that hgPSC-derived cardiac cells could integrate into cardiac tissue in vivo. Note, while the work presented here was based on testes-derived hgPSCs, data from other laboratories have shown that ovaries contain very similar types of stem cells that can give rise to hgPSCs. As a result, hgPSCs should be considered a viable option for eventual use in patients, male or female, with ischemic heart disease

A novel neuregulin - jagged1 paracrine loop in breast cancer transendothelial migration

Background

The interaction of breast cancer cells with other cells in the tumor microenvironment plays an important role in metastasis. Invasion and intravasation, two critical steps in the metastatic process, are influenced by these interactions. Macrophages are of particular interest when it comes to studying tumor cell invasiveness. Previous studies have shown that there is paracrine loop signaling between breast cancer cells and macrophages involving colony stimulating factor 1 (CSF-1) produced by tumor cells and epidermal growth factor (EGF) production by macrophages. In this paper, we identify a novel paracrine loop between tumor cells and macrophages involving neuregulin (NRG1) and notch signaling.

Methods

The aim of this study was to determine the role of NRG1, a ligand of the ErbB3 receptor, in macrophage stimulation of tumor cell transendothelial migration and intravasation. We used fluorescence-activated cell sorting (FACS) and western blot to determine ErbB3 and NRG1 expression, respectively. An in vitro transendothelial migration (iTEM) assay was used to examine the effects of short hairpin (sh)RNA targeting NRG1 in tumor cells and clustered regularly interspaced short palindromic repeats (CRISPR) knockout of jagged 1 (JAG1) in macrophages. Orthotopic xenograft injections in mice were used to confirm results in vivo.

Results

In our system, macrophages were the primary cells showing expression of ErbB3, and a blocking antibody against ErbB3 resulted in a significant decrease in macrophage-induced transendothelial migration of breast cancer cells. Stimulation of macrophages with NRG1 upregulated mRNA and protein expression of JAG1, a ligand of the Notch receptor, and JAG1 production by macrophages was important for transendothelial migration of tumor cells.

Conclusions

This study demonstrates that stimulation of macrophages by tumor cell NRG1 can enhance transendothelial migration and intravasation. We also demonstrate that this effect is due to induction of macrophage JAG1, an important ligand of the Notch signaling pathway.

Neuregulin-1 is a chemoattractant and chemokinetic molecule for trunk neural crest cells

BACKGROUND

Trunk neural crest cells migrate rapidly along characteristic pathways within the developing vertebrate embryo. Proper trunk neural crest cell migration is necessary for the morphogenesis of much of the peripheral nervous system, melanocytes, and the adrenal medulla. Numerous molecules help guide trunk neural crest cell migration throughout the early embryo.

RESULTS

The trophic factor NRG1 is a chemoattractant through in vitro chemotaxis assays and in vivo silencing via a DN-erbB receptor. Interestingly, we also observed changes in migratory responses consistent with a chemokinetic effect of NRG1 in trunk neural crest velocity.

CONCLUSIONS

NRG1 is a trunk neural crest cell chemoattractant and chemokinetic molecule. Developmental Dynamics 247:888-902, 2018.. © 2018 Wiley Periodicals, Inc.

ErbB2 promotes endothelial phenotype of human left ventricular epicardial highly proliferative cells (eHiPC)

The adult human heart contains a subpopulation of highly proliferative cells. The role of ErbB receptors in these cells has not been studied. From human left ventricular (LV) epicardial biopsies, we isolated highly proliferative cells (eHiPC) to characterize the cell surface expression and function of ErbB receptors in the regulation of cell proliferation and phenotype. We found that human LV eHiPC express all four ErbB receptor subtypes. However, the expression of ErbB receptors varied widely among eHiPC isolated from different subjects. eHiPC with higher cell surface expression of ErbB2 reproduced the phenotype of endothelial cells and were characterized by endothelial cell-like functional properties. We also found that EGF/ErbB1 induces VEGFR2 expression, while ligands for both ErbB1 and ErbB3/4 induce expression of Tie2. The number of CD31posCD45neg endothelial cells is higher in LV biopsies from subjects with high ErbB2 (ErbB2high) eHiPC compared to low ErbB2 (ErbB2low) eHiPC. These findings have important implications for potential strategies to increase the efficacy of cell-based revascularization of the injured heart, through promotion of an endothelial phenotype in cardiac highly proliferative cells.

An essential role for neuregulin-4 in the growth and elaboration of developing neocortical pyramidal dendrites

Neuregulins, with the exception of neuregulin-4 (NRG4), have been shown to be extensively involved in many aspects of neural development and function and are implicated in several neurological disorders, including schizophrenia, depression and bipolar disorder. Here we provide the first evidence that NRG4 has a crucial function in the developing brain. We show that both the apical and basal dendrites of neocortical pyramidal neurons are markedly stunted in Nrg4^-/- neonates in vivo compared with Nrg4^+/+ littermates. Neocortical pyramidal neurons cultured from Nrg4^-/- embryos had significantly shorter and less branched neurites than those cultured from Nrg4^+/+ littermates. Recombinant NRG4 rescued the stunted phenotype of embryonic neocortical pyramidal neurons cultured from Nrg4^-/- mice. The majority of cultured wild type embryonic cortical pyramidal neurons co-expressed NRG4 and its receptor ErbB4. The difference between neocortical pyramidal dendrites of Nrg4^-/- and Nrg4^+/+ mice was less pronounced, though still significant, in juvenile mice. However, by adult stages, the pyramidal dendrite arbors of Nrg4^-/- and Nrg4^+/+ mice were similar, suggesting that compensatory changes in Nrg4^-/- mice occur with age. Our findings show that NRG4 is a major novel regulator of dendritic arborisation in the developing cerebral cortex and suggest that it exerts its effects by an autocrine/paracrine mechanism.

Isolation of Schwann Cell Precursors from Rodents

Schwann cell precursors are the first defined stage in the generation of Schwann cells from the neural crest and represent the glial cell of embryonic nerves. Highly pure cultures of these cells can be obtained by enzymatic dissociation of nerves dissected from the limbs of 14- or 12-day-old rat and mouse embryos, respectively. Since Schwann cell precursors, unlike Schwann cells, are acutely dependent on axonal signals for survival, they require addition of trophic factors, typically β-neuregulin-1, for maintenance in cell culture. Under these conditions they convert to Schwann cells on schedule, within about 4 days.

Resistance to receptor-blocking therapies primes tumors as targets for HER3-homing nanobiologics

Resistance to anti-tumor therapeutics is an important clinical problem. Tumor-targeted therapies currently used in the clinic are derived from antibodies or small molecules that mitigate growth factor activity. These have improved therapeutic efficacy and safety compared to traditional treatment modalities but resistance arises in the majority of clinical cases. Targeting such resistance could improve tumor abatement and patient survival. A growing number of such tumors are characterized by prominent expression of the human epidermal growth factor receptor 3 (HER3) on the cell surface. This study presents a “Trojan-Horse” approach to combating these tumors by using a receptor-targeted biocarrier that exploits the HER3 cell surface protein as a portal to sneak therapeutics into tumor cells by mimicking an essential ligand. The biocarrier used here combines several functions within a single fusion protein for mediating targeted cell penetration and non-covalent self-assembly with therapeutic cargo, forming HER3-homing nanobiologics. Importantly, we demonstrate here that these nanobiologics are therapeutically effective in several scenarios of resistance to clinically approved targeted inhibitors of the human EGF receptor family. We also show that such inhibitors heighten efficacy of our nanobiologics on naïve tumors by augmenting HER3 expression. This approach takes advantage of a current clinical problem (i.e. resistance to growth factor inhibition) and uses it to make tumors more susceptible to HER3 nanobiologic treatment. Moreover, we demonstrate a novel approach in addressing drug resistance by taking inhibitors against which resistance arises and re-introducing these as adjuvants, sensitizing tumors to the HER3 nanobiologics described here.

Slowing disease progression in the SOD1 mouse model of ALS by blocking neuregulin-induced microglial activation

There are no effective treatments to slow disease progression in ALS. We previously reported that neuregulin (NRG) receptors are constitutively activated on microglia in the ventral horns in both ALS patients and SOD1 mice and in the corticospinal tracts of ALS patients, and that NRG receptor activation occurs prior to significant clinical disease onset in SOD1 mice. Here, we hypothesize that blocking NRG signaling on microglia would slow disease progression in SOD1 mice using a targeted NRG antagonist (HBD-S-H4). Recombinant HBD-S-H4 directly delivered into the central nervous system (CNS) through implanted intracerebroventricular cannulas showed no signs of toxicity and significantly inhibited NRG receptor activation on microglia resulting in reduced microglial activation and motor neuron loss. The treatment also resulted in a delay in disease onset and an increase in survival. The therapeutic effect was dose-dependent that varied as a function of genetic background in two different strains of SOD1 mice. As a complementary drug delivery approach, transgenic mice expressing HBD-S-H4 driven by an astrocytic promoter (GFAP) had slower disease progression in a dose dependent manner, based on the level of HBD-S-H4 expression. These studies provide mechanistic insights into how NRG signaling on microglia may lead to disease progression and demonstrate the utility of a humanized fusion protein that blocks NRG as a novel therapeutic for human ALS.

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.

Neuregulin-1β induces proliferation, survival and paracrine signaling in normal human cardiac ventricular fibroblasts

Neuregulin-1β (NRG-1β) is critical for cardiac development and repair, and recombinant forms are currently being assessed as possible therapeutics for systolic heart failure. We previously demonstrated that recombinant NRG-1β reduces cardiac fibrosis in an animal model of cardiac remodeling and heart failure, suggesting that there may be direct effects on cardiac fibroblasts. Here we show that NRG-1β receptors (ErbB2, ErbB3, and ErbB4) are expressed in normal human cardiac ventricular (NHCV) fibroblast cell lines. Treatment of NHCV fibroblasts with recombinant NRG-1β induced activation of the AKT pathway, which was phosphoinositide 3-kinase (PI3K)-dependent. Moreover, the NRG-1β-induced PI3K/AKT signaling in these cells required phosphorylation of both ErbB2 and ErbB3 receptors at tyrosine (Tyr)1248 and Tyr1289 respectively. RNASeq analysis of NRG-1β-treated cardiac fibroblasts obtained from three different individuals revealed a global gene expression signature consistent with cell growth and survival. We confirmed enhanced cellular proliferation and viability in NHCV fibroblasts in response to NRG-1β, which was abrogated by PI3K, ErbB2, and ErbB3 inhibitors. NRG-1β also induced production and secretion of cytokines (interleukin-1α and interferon-γ) and pro-reparative factors (angiopoietin-2, brain-derived neurotrophic factor, and crypto-1), suggesting a role in cardiac repair through the activation of paracrine signaling.

Temporal, Diagnostic, and Tissue-Specific Regulation of NRG3 Isoform Expression in Human Brain Development and Affective Disorders

OBJECTIVE

Genes implicated in schizophrenia are enriched in networks differentially regulated during human CNS development. Neuregulin 3 (NRG3), a brain-enriched neurotrophin, undergoes alternative splicing and is implicated in several neurological disorders with developmental origins. Isoform-specific increases in NRG3 are observed in schizophrenia and associated with rs10748842, a NRG3 risk polymorphism, suggesting NRG3 transcriptional dysregulation as a molecular mechanism of risk. The authors quantitatively mapped the temporal trajectories of NRG3 isoforms (classes I-IV) in the neocortex throughout the human lifespan, examined whether tissue-specific regulation of NRG3 occurs in humans, and determined if abnormalities in NRG3 transcriptomics occur in mood disorders and are genetically determined.

METHOD

NRG3 isoform classes I-IV were quantified using quantitative real-time polymerase chain reaction in human postmortem dorsolateral prefrontal cortex from 286 nonpsychiatric control individuals, from gestational week 14 to 85 years old, and individuals diagnosed with either bipolar disorder (N=34) or major depressive disorder (N=69). Tissue-specific mapping was investigated in several human tissues. rs10748842 was genotyped in individuals with mood disorders, and association with NRG3 isoform expression examined.

RESULTS

NRG3 classes displayed individually specific expression trajectories across human neocortical development and aging; classes I, II, and IV were significantly associated with developmental stage. NRG3 class I was increased in bipolar and major depressive disorder, consistent with observations in schizophrenia. NRG3 class II was increased in bipolar disorder, and class III was increased in major depression. The rs10748842 risk genotype predicted elevated class II and III expression, consistent with previous reports in the brain, with tissue-specific analyses suggesting that classes II and III are brain-specific isoforms of NRG3.

CONCLUSIONS

Mapping the temporal expression of genes during human brain development provides vital insight into gene function and identifies critical sensitive periods whereby genetic factors may influence risk for psychiatric disease. Here the authors provide comprehensive insight into the transcriptional landscape of the psychiatric risk gene, NRG3, in human neocortical development and expand on previous findings in schizophrenia to identify increased expression of developmentally and genetically regulated isoforms in the brain of patients with mood disorders. Principally, the finding that NRG3 classes II and III are brain-specific isoforms predicted by rs10748842 risk genotype and are increased in mood disorders further implicates a molecular mechanism of psychiatric risk at the NRG3 locus and identifies a potential developmental role for NRG3 in bipolar disorder and major depression. These observations encourage investigation of the neurobiology of NRG3 isoforms and highlight inhibition of NRG3 signaling as a potential target for psychiatric treatment development.

Microglia-derived neuregulin expression in psychiatric disorders

Several studies have revealed that neuregulins (NRGs) are involved in brain function and psychiatric disorders. While NRGs have been regarded as neuron- or astrocyte-derived molecules, our research has revealed that microglia also express NRGs, levels of which are markedly increased in activated microglia. Previous studies have indicated that microglia are activated in the brains of individuals with autism spectrum disorder (ASD). Therefore, we investigated microglial NRG mRNA expression in multiple lines of mice considered models of ASD. Intriguingly, microglial NRG expression significantly increased in BTBR and socially-isolated mice, while maternal immune activation (MIA) mice exhibited identical NRG expression to controls. Furthermore, we observed a positive correlation between NRG expression in microglia and peripheral blood mononuclear cells (PBMCs) in mice, suggesting that NRG expression in human PBMCs may mirror microglia-derived NRG expression in the human brain. To translate these findings for application in clinical psychiatry, we measured levels of NRG1 splice-variant expression in clinically available PBMCs of patients with ASD. Levels of NRG1 type III expression in PBMCs were positively correlated with impairments in social interaction in children with ASD (as assessed using the Autistic Diagnostic Interview-Revised test: ADI-R). These findings suggest that immune cell-derived NRGs may be implicated in the pathobiology of psychiatric disorders such as ASD.

Tanapoxvirus lacking a neuregulin-like gene regresses human melanoma tumors in nude mice

Neuregulin (NRG), an epidermal growth factor is known to promote the growth of various cell types, including human melanoma cells through ErbB family of tyrosine kinases receptors. Tanapoxvirus (TPV)-encoded protein TPV-15L, a functional mimic of NRG, also acts through ErbB receptors. Here, we show that the TPV-15L protein promotes melanoma proliferation. TPV recombinant generated by deleting the 15L gene (TPVΔ15L) showed replication ability similar to that of wild-type TPV (wtTPV) in owl monkey kidney cells, human lung fibroblast (WI-38) cells, and human melanoma (SK-MEL-3) cells. However, a TPV recombinant with both 15L and the thymidine kinase (TK) gene 66R ablated (TPVΔ15LΔ66R) replicated less efficiently compared to TPVΔ15L and the parental virus. TPVΔ15L exhibited more robust tumor regression in the melanoma-bearing nude mice compared to other TPV recombinants. Our results indicate that deletion of TPV-15L gene product which facilitates the growth of human melanoma cells can be an effective strategy to enhance the oncolytic potential of TPV for the treatment of melanoma.

Neuregulin-1 mutant mice indicate motor and sensory deficits, indeed few references for schizophrenia endophenotype model

Neuregulins (Nrg) are a gene family that binds to tyrosine kinase receptors of the ErbB family. The protein of Nrg1 is to be involved in heart formation, migration of neurons, axonal pathfinding and synaptic function. A relation between Nrg1 and schizophrenia is assumed. Chronic impairment in schizophrenia is characterized by different positive and negative symptoms. Detectable markers of this disease in human and in animal models are activity, social behavior and sensory processing. In this study we compared heterozygous Nrg1 mutant mice in behavior and quantification of dopaminergic and serotoninergic neurons with wild type-like littermates. In the Nrg1 mutant mice the epidermal growth factor-like domain is replaced by the neomycin resistance gene. We found significant differences in locomotor and pain perception behavior. No differences were found in specific schizophrenia social interaction and prepulse inhibition behavior. The number of dopaminergic and serotoninergic neurons did not differ in the investigated regions ventral tegmental area, substantia nigra, periaqueductal grey and raphe nuclei. In conclusion, this analyzed Nrg1 mutant mice model did not serve as a complete schizophrenia model. Particular aspects of schizophrenia disease in locomotor and sensory behavior deficits could represent in this Nrg1 mutant mice. Beside several different models could Nrg1 deficiency represent an endophenotype of schizophrenia disease.

Effects of neuregulin GGF2 (cimaglermin alfa) dose and treatment frequency on left ventricular function in rats following myocardial infarction

Neuregulins are important growth factors involved in cardiac development and response to stress. Certain isoforms and fragments of neuregulin have been found to be cardioprotective. The effects of a full-length neuregulin-1β isoform, glial growth factor 2 (GGF2; USAN/INN; also called cimaglermin) were investigated in vitro. Various dosing regimens were then evaluated for their effects on left ventricular (LV) function in rats with surgically-induced myocardial infarction. In vitro, GGF2 bound with high affinity to erythroblastic leukemia viral oncogene (ErbB) 4 receptors, potently promoted Akt phosphorylation, as well as reduced cell death following doxorubicin exposure in HL1 cells. Daily GGF2 treatment beginning 7-14 days after left anterior descending coronary artery ligation produced improvements in LV ejection fraction and other measures of LV function and morphology. The improvements in LV function (e.g. 10% point increase in absolute LV ejection fraction) with GGF2 were dose-dependent. LV performance was substantially improved when GGF2 treatment was delivered infrequently, despite a serum half-life of less than 2h and could be maintained for more than 10 months with treatment once weekly or once every 2 weeks. These studies confirm previous findings that GGF2 may improve contractile performance in the failing rat heart and that infrequent exposure to GGF2 may improve LV function and impact remodeling in the failing myocardium. GGF2 is now being developed for the treatment of heart failure in humans.

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

Background

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

Methods

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

Results

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

Conclusions

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

Expression level of miRNAs on chromosome 14q32.31 region correlates with tumor aggressiveness and survival of glioblastoma patients

The 54 microRNAs (miRNAs) within the DLK-DIO3 genomic region on chromosome 14q32.31 (cluster-14-miRNAs) are organized into sub-clusters 14A and 14B. These miRNAs are downregulated in glioblastomas and might have a tumor suppressive role. Any association between the expression levels of cluster-14-miRNAs with overall survival (OS) is undetermined. We randomly selected miR-433, belonging to sub-cluster 14A and miR-323a-3p and miR-369-3p, belonging to sub-cluster 14B, and assessed their role in glioblastomas in vitro and in vivo. We also determined the expression level of cluster-14-miRNAs in 27 patients with newly diagnosed glioblastoma, and analyzed the association between their level of expression and OS. Overexpression of miR-323a-3p and miR-369-3p, but not miR-433, in glioblastoma cells inhibited their proliferation and migration in vitro. Mice implanted with glioblastoma cells overexpressing miR323a-3p and miR369-3p, but not miR433, exhibited prolonged survival compared to controls (P = .003). Bioinformatics analysis identified 13 putative target genes of cluster-14-miRNAs, and real-time RT-PCR validated these findings. Pathway analysis of the putative target genes identified neuregulin as the most enriched pathway. The expression level of cluster-14-miRNAs correlated with patients' OS. The median OS was 8.5 months for patients with low expression levels and 52.7 months for patients with high expression levels (HR 0.34; 95 % CI 0.12-0.59, P = .003). The expression level of cluster-14-miRNAs correlates directly with OS, suggesting a role for this cluster in promoting aggressive behavior of glioblastoma, possibly through ErBb/neuregulin signaling.

Proteolytic processing of Neuregulin-1

Neuregulin-1 (NRG1), known also as heregulin, acetylcholine receptor inducing activity (ARIA), glial growth factor (GGF), or sensory and motor neuron derived factor (SMDF), is a key factor for many developmental processes and in adult brain. All known splice variants contain an epidermal growth factor (EGF)-like domain, which is mediating signaling via receptors of the ErbB family. In particular, NRG1 acts as an essential signaling molecule expressed on the axonal surface, where it signals to Schwann cells throughout development and regulates the thickness of the myelin sheath. NRG1 is required also by other cell types in the nervous system, for instance as an axonal signal released by proprioceptive afferents to induce development of the muscle spindle, and it controls aspects of cortical interneuron development as well as the formation of thalamo-cortical projections. The precursor protein of NRG1 can be activated and released from the membrane through limited proteolysis by the β-Secretase (β-site amyloid precursor protein cleaving enzyme 1, BACE1) which was first identified through its function as the rate limiting enzyme of amyloid-β-peptide (Aβ) production. Aβ is the major component of amyloid plaques in Alzheimer's disease (AD). Due to the hairpin nature of NRG1 type III two membrane-bound stubs with a type 1 and a type 2 orientation are generated by an initial proteolytic cleavage and successive release of the EGF-like domain either by dual cleavage by BACE1 or by ADAM17 (a disintegrin and metalloprotease) which is also called TACE (Tumor Necrosis Factor-α-converting enzyme). The cleavages activate NRG1 to allow juxtacrine or paracrine signaling. The type 1 oriented stub is further cleaved by γ-secretase in the transmembrane domain with a putative role in intracellular domain (ICD) signaling, while the type II oriented stub is cleaved by signal peptidase like proteases (SPPLs). Neuregulin-1 was identified as a major physiological substrate of BACE1 during early postnatal development when similarities in BACE1 KO mice and NRG1 heterozygous mice were discovered. Both display severe hypomyelination of peripheral nerves. Later it was shown with genetic and pharmacological evidence that the developmental effect of type I NRG1 on the formation and the maintenance of muscle spindles is BACE1 dependent. Thus, NRG1 functions in PNS and CNS are likely to set limits to an Alzheimer disease therapy with relatively strong BACE1 inhibition.

Functional impact of sarcopenia in respiratory muscles

The risk for respiratory complications and infections is substantially increased in old age, which may be due, in part, to sarcopenia (aging-related weakness and atrophy) of the diaphragm muscle (DIAm), reducing its force generating capacity and impairing the ability to perform expulsive non-ventilatory motor behaviors critical for airway clearance. The aging-related reduction in DIAm force generating capacity is due to selective atrophy of higher force generating type IIx and/or IIb muscle fibers, whereas lower force generating type I and IIa muscle fiber sizes are preserved. Fiber type specific DIAm atrophy is also seen following unilateral phrenic nerve denervation and in other neurodegenerative disorders. Accordingly, the effect of aging on DIAm function resembles that of neurodegeneration and suggests possible common mechanisms, such as the involvement of several neurotrophic factors in mediating DIAm sarcopenia. This review will focus on changes in two neurotrophic signaling pathways that represent potential mechanisms underlying the aging-related fiber type specific DIAm atrophy.

Specific Inhibition of β-Secretase Processing of the Alzheimer Disease Amyloid Precursor Protein

Development of disease-modifying therapeutics is urgently needed for treating Alzheimer disease (AD). AD is characterized by toxic β-amyloid (Aβ) peptides produced by β- and γ-secretase-mediated cleavage of the amyloid precursor protein (APP). β-secretase inhibitors reduce Aβ levels, but mechanism-based side effects arise because they also inhibit β-cleavage of non-amyloid substrates like Neuregulin. We report that β-secretase has a higher affinity for Neuregulin than it does for APP. Kinetic studies demonstrate that the affinities and catalytic efficiencies of β-secretase are higher toward non-amyloid substrates than toward APP. We show that non-amyloid substrates are processed by β-secretase in an endocytosis-independent manner. Exploiting this compartmentalization of substrates, we specifically target the endosomal β-secretase by an endosomally targeted β-secretase inhibitor, which blocked cleavage of APP but not non-amyloid substrates in many cell systems, including induced pluripotent stem cell (iPSC)-derived neurons. β-secretase inhibitors can be designed to specifically inhibit the Alzheimer process, enhancing their potential as AD therapeutics without undesired side effects.

Development of an ErbB4 monoclonal antibody that blocks neuregulin-1-induced ErbB4 activation in cancer cells

The use of monoclonal antibodies (mAbs) for cancer therapy is one of the most important strategies for current cancer treatment. The epidermal growth factor receptor (EGFR) family of receptor tyrosine kinases, which regulates cancer cell proliferation, survival, and migration, is a major molecular target for antibody-based therapy. ErbB4/HER4, which contains a ligand-binding extracellular region, is activated by several ligands, including neuregulins (NRGs), heparin-binding EGF-like growth factor, betacellulin and epiregulin. Although there are clinically approved antibodies for ErbB1 and ErbB2, there are no available therapeutic mAbs for ErbB4, and it is not known whether ErbB4 is a useful target for antibody-based cancer therapy. In this study, we developed an anti-ErbB4 mAb (clone P6-1) that suppresses NRG-dependent activation of ErbB4 and examined its effect on breast cancer cell proliferation in the extracellular matrix.

Identification of the neural crest-specific enhancer of Seraf gene in avian peripheral nervous system development

In vertebrate embryos, trunk neural crest cells give rise to Schwann cells, along with other derivatives. In this study, to elucidate the molecular mechanisms for the Schwann cell specification, we aimed to identify enhancer elements responsible for the expression of the Seraf gene, the earliest marker for the Schwann cell precursors in the avian embryos. We first compared the genomic structure around the Seraf locus in various vertebrates, and found that, while mammals do not have a Seraf homolog, teleost fish species have it. However, the intergenic sequences around the Seraf locus are not conserved between zebrafish and chicken, consistent with the fact that fish Seraf expression is not Schwann cell precursor-specific. We thus compared the intergenic sequences around the Seraf locus among avian species, and identified a potential enhancer containing a cluster of Sox10-binding sites. Accordingly, the identified enhancer is activated in a neural crest-specific manner in transfected quail embryos. We also found that Sox10 activated the enhancer in cultured cells. Thus, our results revealed a new role of Sox10 in the earliest phase of the Schwann cell fate specification.

Neuregulin-1 improves right ventricular function and attenuates experimental pulmonary arterial hypertension

AIMS

Pulmonary arterial hypertension (PAH) is a serious disease that affects both the pulmonary vasculature and the right ventricle (RV). Current treatment options are insufficient. The cardiac neuregulin (NRG)-1/ErbB system is deregulated during heart failure, and treatment with recombinant human NRG-1 (rhNRG-1) has been shown to be beneficial in animal models and in patients with left ventricular (LV) dysfunction. This study aimed to evaluate the effects of rhNRG-1 in RV function and pulmonary vasculature in monocrotaline (MCT)-induced PAH and RV hypertrophy (RVH).

METHODS AND RESULTS

Male wistar rats (7- to 8-weeks old, n = 78) were injected with MCT (60 mg/kg, s.c.) or saline and treated with rhNRG-1 (40 µg/kg/day) or vehicle for 1 week, starting 2 weeks after MCT administration. Another set of animals was submitted to pulmonary artery banding (PAB) or sham surgery, and followed the same protocol. MCT administration resulted in the development of PAH, pulmonary arterial and RV remodelling, and dysfunction, and increased RV markers of cardiac damage. Treatment with rhNRG-1 attenuated RVH, improved RV function, and decreased RV expression of disease markers. Moreover, rhNRG-1 decreased pulmonary vascular remodelling and attenuated MCT-induced endothelial dysfunction. The anti-remodelling effects of rhNRG-1 were confirmed in the PAB model, where rhNRG-1 treatment was able to attenuate PAB-induced RVH.

CONCLUSION

rhNRG-1 treatment attenuates pulmonary arterial and RV remodelling, and dysfunction in a rat model of MCT-induced PAH and has direct anti-remodelling effects on the pressure-overloaded RV.

Decreased plasma levels of neureglin-1 in drug naïve patients and chronic patients with schizophrenia

Although the neuregulin-1 (NRG1) gene is one of the susceptibility genes for schizophrenia and various other psychiatric diseases, it remains unclear how individual psychiatric diseases affect the expression of the NRG1 protein in patients. A previous study reported a schizophrenia-linked decrease in serum NRG1 levels. The present study aimed to replicate this initial finding and to assess its disease specificity for schizophrenia. We collected plasma samples from drug-naïve patients with first-episode schizophrenia (n=80), patients with chronic schizophrenia (n=86), patients with bipolar I disorder (n=60), patients with bipolar II disorder (n=60) and patients with major depressive disorder (n=60), we measured the plasma levels of NRG1β1 and compared the levels with those of age- and sex-matched healthy volunteers (n=82). One-way ANOVA and post hoc analyses detected specific NRG1β1 decreases in the participants with first-episode and chronic schizophrenia but not in those with bipolar I disorder, bipolar II disorder or major depressive disorder. The mean plasma levels of NRG1β1 immunoreactivity were 4.27±0.71 ng/mL in the participants with first-episode schizophrenia, 4.08±0.64 ng/mL in the participants with chronic schizophrenia and 7.21±0.91 ng/mL in the healthy controls. Although we analyzed the pathological correlations of NRG1β1 immunoreactivity in terms of the clinical parameters of the sample, we observed only weak positive correlations with the age of the participants with chronic schizophrenia and the disease onset times of the participants with bipolar II disorder. We failed to identify correlations between other clinical parameters and plasma NRG1β1 immunoreactivity among all patient subjects. These findings suggest that NRG1 may serve as a relatively specific disease marker for schizophrenia. However, the pathological role of this decrease must be explored further.

Promotion of periostin expression contributes to the migration of Schwann cells

Neuregulin ligands and their ErbB receptors are important for the development of Schwann cells, the glial cells of the peripheral nervous system (PNS). ErbB3 deficiency is characterized by a complete loss of Schwann cells along axons of the peripheral nerves, impaired fasciculation and neuronal cell death. We performed comparative gene expression analysis of dorsal root ganglia (DRG) explant cultures from ErbB3-deficient and wild-type mice in order to identify genes that are involved in Schwann cell development and migration. The extracellular matrix (ECM) gene periostin was found to exhibit the most prominent down regulation in ErbB3-deficient DRG. Expression analysis revealed that the periostin-expressing cell population in the PNS corresponds to Schwann cell precursors and Schwann cells, and is particularly high in migratory Schwann cells. Furthermore, stimulation of Schwann cells with neuregulin-1 (NRG1) or transforming growth factor β (TGFβ-1) resulted in an upregulation of periostin expression. Interestingly, DRG explant cultures of periostin-deficient mice revealed a significant reduction of the number of migrating Schwann cells. These data demonstrate that the expression of periostin is stimulated by ErbB ligand NRG1 and influences the migration of Schwann cell precursors.

Axonal wrapping in the Drosophila PNS is controlled by glia-derived neuregulin homolog Vein

Efficient neuronal conductance requires that axons are insulated by glial cells. For this, glial membranes need to wrap around axons. Invertebrates show a relatively simple extension of glial membranes around the axons, resembling Remak fibers formed by Schwann cells in the mammalian peripheral nervous system. To unravel the molecular pathways underlying differentiation of glial cells that provide axonal wrapping, we are using the genetically amenable Drosophila model. At the end of larval life, the wrapping glia differentiates into very large cells, spanning more than 1 mm of axonal length. The extension around axonal membranes is not influenced by the caliber of the axon or its modality. Using cell type-specific gene knockdown we show that the extension of glial membranes around the axons is regulated by an autocrine activation of the EGF receptor through the neuregulin homolog Vein. This resembles the molecular mechanism employed during cell-autonomous reactivation of glial differentiation after injury in mammals. We further demonstrate that Vein, produced by the wrapping glia, also regulates the formation of septate junctions in the abutting subperineurial glia. Moreover, the wrapping glia indirectly controls the proliferation of the perineurial glia. Thus, the wrapping glia appears center stage to orchestrate the development of the different glial cell layers in a peripheral nerve.