Visualization of Neuregulin 1 ectodomain shedding reveals its local processing in vitro and in vivo

The subventricular zone neurogenic niche provides adult born functional neurons to repair cortical brain injuries in response to diterpenoid therapy

INTRODUCTION

Neural stem cells from the subventricular zone (SVZ) neurogenic niche provide neurons that integrate in the olfactory bulb circuitry. However, in response to cortical injuries, the neurogenic activity of the SVZ is significantly altered, leading to increased number of neuroblasts with a modified migration pattern that leads cells towards the site of injury. Despite the increased neurogenesis and migration, many newly generated neurons fail to survive or functionally integrate into the cortical circuitry. Providing the injured area with the adequate signaling molecules may improve both migration and functional integration of newly generated neurons.

METHODS

In here, we have studied the effect of a diterpene with the capacity to induce neuregulin release at promoting neurogenesis in a murine model of cortical brain injury. Using green fluorescent protein expressing vectors we have labeled SVZ cells and have studied the migration of newly generated neuroblasts toward the injury in response the treatment. In addition, using electrophysiological recordings we have studied the differentiation of these neuroblasts into mature neurons and their functional integration into the cortical circuitry. We have studied their electrical properties, their morphology and cortical location.

RESULTS

We have found that EOF2 treatment of adult mice with mechanical cortical injuries facilitates the delivery of neuroblasts into these injuries. The newly generated neurons develop features of fully functional neurons. Our results show that the newly generated neurons receive electrical inputs, fire action potentials, and undergo complete differentiation into neurons recapitulating the stages that distinguish ontogenic differentiation. These neurons develop features representative of neurons belonging the cortical layer in which they are situated. We have also studied that EOF2 facilitates neuregulin release in SVZ cells, a signaling factor that promotes neuronal differentiation. Neuregulin is expressed in microglial cells that reach the injury in response to the damage and its release is increased by EOF2 treatment.

CONCLUSION

Promoting neuregulin release via diterpene treatment facilitates migration of SVZ-derived neuroblasts to cortical injuries stimulating their differentiation into mature functional neurons, which receive electrical inputs and develop features of cortical neurons. These findings highlight the role of diterpenoids as a potential therapy to repair cortical brain injuries.

Effect of lathyrane-type diterpenoids in neural stem cell physiology: Microbial transformations, molecular docking and dynamics studies

Promoting endogenous neurogenesis for brain repair is emerging as a promising strategy to mitigate the functional impairments associated with various neurological disorders characterized by neuronal death. Diterpenes featuring tigliane, ingenane, jatrophane and lathyrane skeletons, frequently found in Euphorbia plant species, are known protein kinase C (PKC) activators and exhibit a wide variety of pharmacological properties, including the stimulation of neurogenesis. Microbial transformation of these diterpenes represents a green and sustainable methodology that offers a hitherto little explored approach to obtaining novel derivatives and exploring structure-activity relationships. In the present study, we report the biotransformation of euphoboetirane A (4) and epoxyboetirane A (5), two lathyrane diterpenoids isolated from Euphorbia boetica, by Mucor circinelloides MC NRRL3631. Our findings revealed the production of nine biotransformation products (6-14), including jatrophane derivatives originated through an unprecedented rearrangement from the parent lathyranes. The chemical structures and absolute configurations of the new compounds were elucidated through comprehensive analysis using NMR and ECD spectroscopy, as well as MS. The study evaluated how principal metabolites and their derivatives affect TGFα and NRG1 release, as well as their potential to promote proliferation or differentiation in cultures of NSC isolated from the SVZ of adult mice. In order to shed some light on the mechanisms underlying the ability of 12 as a neurogenic compound, the interactions of selected compounds with PKC δ-C1B were analyzed through molecular docking and molecular dynamics. Based on these, it clearly appears that the ability of compound 12 to form both acceptor and donor hydrogen bonds with certain amino acid residues in the enzyme pocket leads to a higher affinity compound-PKC complex, which correlates with the observed biological activity.

Low-affinity ligands of the epidermal growth factor receptor are long-range signal transmitters in collective cell migration of epithelial cells

Canonical epidermal growth factor (EGF) receptor (EGFR) activation involves the binding of seven EGFR ligands (EGFRLs); however, their extracellular dynamics remain elusive. Here, employing fluorescent probes and a tool for triggering ectodomain shedding, we show that epiregulin (EREG), a low-affinity EGFRL, rapidly and efficiently activates EGFR in Madin-Darby canine kidney (MDCK) epithelial cells and mouse epidermis. During collective cell migration, EGFR and extracellular signal-regulated kinase (ERK) activation waves propagate in an a disintegrin and metalloprotease 17 (ADAM17) sheddase- and EGFRL-dependent manner. Upon induced EGFRL shedding, low-affinity ligands EREG and amphiregulin (AREG) mediate faster and broader ERK waves than high-affinity ligands. Tight/adherens junction integrity is essential for ERK activation propagation, suggesting that tight intercellular spaces prefer the low-affinity EGFRLs for efficient signal transmission. In EREG-deficient mice, ERK wave propagation and cell migration were impaired during skin wound repair. We additionally show that heparin-binding EGF-like growth factor (HBEGF) primarily promotes surrounding cell motility. Our findings underscore the pivotal role of low-affinity EGFRLs in rapid intercellular signal transmission.

Low-affinity ligands of the epidermal growth factor receptor are long-range signal transmitters during collective cell migration of epithelial cells

Epidermal growth factor receptor ligands (EGFRLs) consist of seven proteins. In stark contrast to the amassed knowledge concerning the epidermal growth factor receptors themselves, the extracellular dynamics of individual EGFRLs remain elusive. Here, employing fluorescent probes and a tool for triggering ectodomain shedding of EGFRLs, we show that EREG, a low-affinity EGFRL, exhibits the most rapid and efficient activation of EGFR in confluent epithelial cells and mouse epidermis. In Madin-Darby canine kidney (MDCK) renal epithelial cells, EGFR- and ERK-activation waves propagate during collective cell migration in an ADAM17 sheddase- and EGFRL-dependent manner. Upon induction of EGFRL shedding, radial ERK activation waves were observed in the surrounding receiver cells. Notably, the low-affinity ligands EREG and AREG mediated faster and broader ERK waves than the high-affinity ligands. The integrity of tight/adherens junctions was essential for the propagation of ERK activation, implying that the tight intercellular spaces prefer the low-affinity EGFRL to the high-affinity ligands for efficient signal transmission. To validate this observation in vivo , we generated EREG-deficient mice expressing the ERK biosensor and found that ERK wave propagation and cell migration were impaired during skin wound repair. In conclusion, we have quantitatively demonstrated the distinctions among EGFRLs in shedding, diffusion, and target cell activation in physiological contexts. Our findings underscore the pivotal role of low-affinity EGFRLs in rapid intercellular signal transmission.

Heparanase Stimulation of Physiologic Cardiac Hypertrophy Is Suppressed After Chronic Diabetes, Resulting in Cardiac Remodeling and Dysfunction

In addition to controlling smooth muscle tone in coronary vessels, endothelial cells also influence subjacent cardiomyocyte growth. Because heparanase, with exclusive expression in endothelial cells, enables extracellular matrix remodeling, angiogenesis, metabolic reprogramming, and cell survival, it is conceivable that it could also encourage development of cardiac hypertrophy. Global heparanase overexpression resulted in physiologic cardiac hypertrophy, likely an outcome of HSPG clustering and activation of hypertrophic signaling. The heparanase autocrine effect of releasing neuregulin-1 could have also contributed to this overexpression. Hyperglycemia induced by streptozotocin-induced diabetes sensitized the heart to flow-induced release of heparanase and neuregulin-1. Despite this excess secretion, progression of diabetes caused significant gene expression changes related to mitochondrial metabolism and cell death that led to development of pathologic hypertrophy and heart dysfunction. Physiologic cardiac hypertrophy was also observed in rats with cardiomyocyte-specific vascular endothelial growth factor B overexpression. When perfused, hearts from these animals released significantly higher amounts of both heparanase and neuregulin-1. However, subjecting these animals to diabetes triggered robust transcriptome changes related to metabolism and a transition to pathologic hypertrophy. Our data suggest that in the absence of mechanisms that support cardiac energy generation and prevention of cell death, as seen after diabetes, there is a transition from physiologic to pathologic cardiac hypertrophy and a decline in cardiac function.

ARTICLE HIGHLIGHTS

Therapeutic Potential of Targeting Regulated Intramembrane Proteolysis Mechanisms of Voltage-Gated Ion Channel Subunits and Cell Adhesion Molecules

Several integral membrane proteins undergo regulated intramembrane proteolysis (RIP), a tightly controlled process through which cells transmit information across and between intracellular compartments. RIP generates biologically active peptides by a series of proteolytic cleavage events carried out by two primary groups of enzymes: sheddases and intramembrane-cleaving proteases (iCLiPs). Following RIP, fragments of both pore-forming and non-pore-forming ion channel subunits, as well as immunoglobulin super family (IgSF) members, have been shown to translocate to the nucleus to function in transcriptional regulation. As an example, the voltage-gated sodium channel β1 subunit, which is also an IgSF-cell adhesion molecule (CAM), is a substrate for RIP. β1 RIP results in generation of a soluble intracellular domain, which can regulate gene expression in the nucleus. In this review, we discuss the proposed RIP mechanisms of voltage-gated sodium, potassium, and calcium channel subunits as well as the roles of their generated proteolytic products in the nucleus. We also discuss other RIP substrates that are cleaved by similar sheddases and iCLiPs, such as IgSF macromolecules, including CAMs, whose proteolytically generated fragments function in the nucleus. Importantly, dysfunctional RIP mechanisms are linked to human disease. Thus, we will also review how understanding RIP events and subsequent signaling processes involving ion channel subunits and IgSF proteins may lead to the discovery of novel therapeutic targets. SIGNIFICANCE STATEMENT: Several ion channel subunits and immunoglobulin superfamily molecules have been identified as substrates of regulated intramembrane proteolysis (RIP). This signal transduction mechanism, which generates polypeptide fragments that translocate to the nucleus, is an important regulator of gene transcription. RIP may impact diseases of excitability, including epilepsy, cardiac arrhythmia, and sudden death syndromes. A thorough understanding of the role of RIP in gene regulation is critical as it may reveal novel therapeutic strategies for the treatment of previously intractable diseases.

Plasma neuregulin 1 as a synaptic biomarker in Alzheimer's disease: a discovery cohort study

BACKGROUND

Synaptic dysfunction is an early core feature of Alzheimer's disease (AD), closely associated with cognitive symptoms. Neuregulin 1 (NRG1) is a growth and differentiation factor with a key role in the development and maintenance of synaptic transmission. Previous reports have shown that changes in cerebrospinal fluid (CSF) NRG1 concentration are associated with cognitive status and biomarker evidence of AD pathology. Plasma biomarkers reflecting synaptic impairment would be of great clinical interest.

OBJECTIVE

To measure plasma NRG1 concentration in AD patients in comparison with other neurodegenerative disorders and neurological controls (NC) and to study its association with cerebrospinal fluid (CSF) core AD and synaptic biomarkers.

METHODS

This retrospective study enrolled 127 participants including patients with AD at mild cognitive impairment stage (AD-MCI, n = 27) and at dementia stage (n = 35), non-AD dementia (n = 26, Aβ-negative), non-AD MCI (n = 19), and neurological controls (n=20). Plasma and CSF NRG1, as well as CSF core AD biomarkers (Aβ 42/Aβ 40 ratio, phospho-tau, and total tau), were measured using ELISA. CSF synaptic markers were measured using ELISA for GAP-43 and neurogranin and through immunoprecipitation mass spectrometry for SNAP-25.

RESULTS

Plasma NRG1 concentration was higher in AD-MCI and AD dementia patients compared with neurological controls (respectively P = 0.005 and P < 0.001). Plasma NRG1 differentiated AD MCI patients from neurological controls with an area under the curve of 88.3%, and AD dementia patients from NC with an area under the curve of 87.3%. Plasma NRG1 correlated with CSF NRG1 (β = 0.372, P = 0.0056, adjusted on age and sex). Plasma NRG1 was associated with AD CSF core biomarkers in the whole cohort and in Aβ-positive patients (β = -0.197-0.423). Plasma NRG1 correlated with CSF GAP-43, neurogranin, and SNAP-25 (β = 0.278-0.355). Plasma NRG1 concentration correlated inversely with MMSE in the whole cohort and in Aβ-positive patients (all, β = -0.188, P = 0.038; Aβ+: β = -0.255, P = 0.038).

CONCLUSION

Plasma NRG1 concentration is increased in AD patients and correlates with CSF core AD and synaptic biomarkers and cognitive status. Thus, plasma NRG1 is a promising non-invasive biomarker to monitor synaptic impairment in AD.

Molecular probes for cellular imaging of post-translational proteoforms

Specific post-translational modification (PTM) states of a protein affect its property and function; understanding their dynamics in cells would provide deep insight into diverse signaling pathways and biological processes. However, it is not trivial to visualize post-translational modifications in a protein- and site-specific manner, especially in a living-cell context. Herein, we review recent advances in the development of molecular imaging tools to detect diverse classes of post-translational proteoforms in individual cells, and their applications in studying precise roles of PTMs in regulating the function of cellular proteins.

Completion of neuronal remodeling prompts myelination along developing motor axon branches

Neuronal remodeling and myelination are two fundamental processes during neurodevelopment. How they influence each other remains largely unknown, even though their coordinated execution is critical for circuit function and often disrupted in neuropsychiatric disorders. It is unclear whether myelination stabilizes axon branches during remodeling or whether ongoing remodeling delays myelination. By modulating synaptic transmission, cytoskeletal dynamics, and axonal transport in mouse motor axons, we show that local axon remodeling delays myelination onset and node formation. Conversely, glial differentiation does not determine the outcome of axon remodeling. Delayed myelination is not due to a limited supply of structural components of the axon-glial unit but rather is triggered by increased transport of signaling factors that initiate myelination, such as neuregulin. Further, transport of promyelinating signals is regulated via local cytoskeletal maturation related to activity-dependent competition. Our study reveals an axon branch-specific fine-tuning mechanism that locally coordinates axon remodeling and myelination.

Targeting Protein Kinase C in Glioblastoma Treatment

Glioblastoma (GBM) is the most frequent and aggressive primary brain tumor and is associated with a poor prognosis. Despite the use of combined treatment approaches, recurrence is almost inevitable and survival longer than 14 or 15 months after diagnosis is low. It is therefore necessary to identify new therapeutic targets to fight GBM progression and recurrence. Some publications have pointed out the role of glioma stem cells (GSCs) as the origin of GBM. These cells, with characteristics of neural stem cells (NSC) present in physiological neurogenic niches, have been proposed as being responsible for the high resistance of GBM to current treatments such as temozolomide (TMZ). The protein Kinase C (PKC) family members play an essential role in transducing signals related with cell cycle entrance, differentiation and apoptosis in NSC and participate in distinct signaling cascades that determine NSC and GSC dynamics. Thus, PKC could be a suitable druggable target to treat recurrent GBM. Clinical trials have tested the efficacy of PKCβ inhibitors, and preclinical studies have focused on other PKC isozymes. Here, we discuss the idea that other PKC isozymes may also be involved in GBM progression and that the development of a new generation of effective drugs should consider the balance between the activation of different PKC subtypes.

Sex differences in circulating neuregulin1-β1 and β-secretase 1 expression in childhood-onset schizophrenia

OBJECTIVE

Early-onset schizophrenia is a severe and rare form of schizophrenia that is clinically and neurobiologically continuous with the adult form of schizophrenia. Neuregulin1 (NRG1)-mediated signaling is crucial for early neurodevelopment, which exerts its function by limited β-secretase 1 (BACE1) proteolysis processing. However, circulating neuregulin1-β1 (NRG1-β1), an isoform of NRG1, and its cleavage enzyme BACE1 have not been studied in early-onset patients with schizophrenia.

METHODS

In this study, we collected plasma and clinical information from 71 young patients (7 ≤ age years ≤20) with schizophrenia and 53 age- and sex-matched healthy controls. Immunoassay was used to test levels of circulating NRG1-β1 and BACE1 expression. We further analyzed the relationship of disease-onset age and gender with NRG1-β1 and BACE1 levels.

RESULTS

We found that circulating plasma levels of NRG1-β1 were significantly decreased in young patients with early-onset schizophrenia. In males with childhood onset schizophrenia (COS), NRG1-β1 was reduced and was inversely correlated with positive symptom of PANSS; moreover, these male patients with higher plasma BACE1 levels showed more severe general symptoms of PANSS and defective social functioning; whereas, no aforementioned results were found in adolescent-onset schizophrenia (AOS). Notably, young female patients with COS and AOS had no significant change in NRG1-β1 and BACE1, which demonstrated a sex-dependent effect in early-onset schizophrenia.

CONCLUSION

Our results suggest that decreased levels of NRG1-β1 and its cleavage enzyme BACE1 contribute to increased risk of etiology of schizophrenia. Synthetic biomarkers may have clinical applications for the early diagnosis of male COS.

A novel PKC activating molecule promotes neuroblast differentiation and delivery of newborn neurons in brain injuries

Neural stem cells are activated within neurogenic niches in response to brain injuries. This results in the production of neuroblasts, which unsuccessfully attempt to migrate toward the damaged tissue. Injuries constitute a gliogenic/non-neurogenic niche generated by the presence of anti-neurogenic signals, which impair neuronal differentiation and migration. Kinases of the protein kinase C (PKC) family mediate the release of growth factors that participate in different steps of the neurogenic process, particularly, novel PKC isozymes facilitate the release of the neurogenic growth factor neuregulin. We have demonstrated herein that a plant derived diterpene, (EOF2; CAS number 2230806-06-9), with the capacity to activate PKC facilitates the release of neuregulin 1, and promotes neuroblasts differentiation and survival in cultures of subventricular zone (SVZ) isolated cells in a novel PKC dependent manner. Local infusion of this compound in mechanical cortical injuries induces neuroblast enrichment within the perilesional area, and noninvasive intranasal administration of EOF2 promotes migration of neuroblasts from the SVZ towards the injury, allowing their survival and differentiation into mature neurons, being some of them cholinergic and GABAergic. Our results elucidate the mechanism of EOF2 promoting neurogenesis in injuries and highlight the role of novel PKC isozymes as targets in brain injury regeneration.

Neuregulin directed molecular mechanisms of visual cortical plasticity

Experience-dependent critical period (CP) plasticity has been extensively studied in the visual cortex. Monocular deprivation during the CP affects ocular dominance, limits visual performance, and contributes to the pathological etiology of amblyopia. Neuregulin-1 (NRG1) signaling through its tyrosine kinase receptor ErbB4 is essential for the normal development of the nervous system and has been linked to neuropsychiatric disorders such as schizophrenia. We discovered recently that NRG1/ErbB4 signaling in PV neurons is critical for the initiation of CP visual cortical plasticity by controlling excitatory synaptic inputs onto PV neurons and thus PV-cell mediated cortical inhibition that occurs following visual deprivation. Building on this discovery, we review the existing literature of neuregulin signaling in developing and adult cortex and address the implication of NRG/ErbB4 signaling in visual cortical plasticity at the cellular and circuit levels. NRG-directed research may lead to therapeutic approaches to reactivate plasticity in the adult cortex.

Epidermal growth factor receptor: Structure-function informing the design of anticancer therapeutics

Research on the epidermal growth factor (EGF) family and the family of receptors (EGFR) has progressed rapidly in recent times. New crystal structures of the ectodomains with different ligands, the activation of the kinase domain through oligomerisation and the use of fluorescence techniques have revealed profound conformational changes on ligand binding. The control of cell signaling from the EGFR-family is complex, with heterodimerisation, ligand affinity and signaling cross-talk influencing cellular outcomes. Analysis of tissue homeostasis indicates that the control of pro-ligand processing is likely to be as important as receptor activation events. Several members of the EGFR-family are overexpressed and/or mutated in cancer cells. The perturbation of EGFR-family signaling drives the malignant phenotype of many cancers and both inhibitors and antagonists of signaling from these receptors have already produced therapeutic benefits for patients. The design of affibodies, antibodies, small molecule inhibitors and even immunotherapeutic drugs targeting the EGFR-family has yielded promising new approaches to improving outcomes for cancer patients. In this review, we describe recent discoveries which have increased our understanding of the structure and dynamics of signaling from the EGFR-family, the roles of ligand processing and receptor cross-talk. We discuss the relevance of these studies to the development of strategies for designing more effective targeted treatments for cancer patients.

Dysregulation of Neuregulin-1/ErbB signaling in the hippocampus of rats after administration of doxorubicin

Objective

Long-term use of doxorubicin (Dox) can cause neurobiological side effects associated with depression, but the underlying mechanisms remain equivocal. While recent evidence has indicated that Neuregulin-1 (NRG1) and its ErbB receptors play an essential role in neural function, much is still unknown concerning the biological link between the NRG1/ErbB pathway and the Dox-induced neurotoxicity. Therefore, we examined the protein expression of NRG1 and ErbB receptors in the hippocampus of rats following Dox treatment.

Materials and methods

The drug was administered every 2 days at a dose of 2.5 mg/kg, and the animals in different groups were treated with intraperitoneal injection for three or seven times, respectively.

Results

Our data showed that the rats treated with Dox for seven times (DoxL group) exhibited depression-like behaviors, whereas the short-term treatment (DoxS group) had no effect on the behavioral changes. Dox treatment also induced the neural apoptosis with more severe neurotoxicity. Intriguingly, the expression of NRG1 and the ratio of pErbB4/ErbB4 and pErbB2/ErbB2 were significantly decreased in the DoxL group, but enhanced activation of ErbB receptors was observed in the DoxS group. In parallel, administration of Dox for seven times suppressed the downstream Akt and ERK phosphorylation, while the Akt phosphorylation was enhanced with the administration of Dox for three times.

Conclusion

Our data first showed the Dox-induced alterations of the NRG1/ErbB system in the hippocampus, indicating the potential involvement of the NRG1/ErbB pathway in the Dox-induced nervous system dysfunction.

Transposons As Tools for Functional Genomics in Vertebrate Models

Genetic tools and mutagenesis strategies based on transposable elements are currently under development with a vision to link primary DNA sequence information to gene functions in vertebrate models. By virtue of their inherent capacity to insert into DNA, transposons can be developed into powerful tools for chromosomal manipulations. Transposon-based forward mutagenesis screens have numerous advantages including high throughput, easy identification of mutated alleles, and providing insight into genetic networks and pathways based on phenotypes. For example, the Sleeping Beauty transposon has become highly instrumental to induce tumors in experimental animals in a tissue-specific manner with the aim of uncovering the genetic basis of diverse cancers. Here, we describe a battery of mutagenic cassettes that can be applied in conjunction with transposon vectors to mutagenize genes, and highlight versatile experimental strategies for the generation of engineered chromosomes for loss-of-function as well as gain-of-function mutagenesis for functional gene annotation in vertebrate models, including zebrafish, mice, and rats.