ErbB4 signals Neuregulin1-stimulated cell proliferation and c-fos gene expression through phosphorylation of serum response factor by mitogen-activated protein kinase cascade

The multifaceted role of kinases in amyotrophic lateral sclerosis: genetic, pathological and therapeutic implications

Amyotrophic lateral sclerosis is the most common degenerative disorder of motor neurons in adults. As there is no cure, thousands of individuals who are alive at present will succumb to the disease. In recent years, numerous causative genes and risk factors for amyotrophic lateral sclerosis have been identified. Several of the recently identified genes encode kinases. In addition, the hypothesis that (de)phosphorylation processes drive the disease process resulting in selective motor neuron degeneration in different disease variants has been postulated. We re-evaluate the evidence for this hypothesis based on recent findings and discuss the multiple roles of kinases in amyotrophic lateral sclerosis pathogenesis. We propose that kinases could represent promising therapeutic targets. Mainly due to the comprehensive regulation of kinases, however, a better understanding of the disturbances in the kinome network in amyotrophic lateral sclerosis is needed to properly target specific kinases in the clinic.

Benzydamine inhibits osteoclast differentiation and bone resorption via down-regulation of interleukin-1 β expression

Bone diseases such as osteoporosis and periodontitis are induced by excessive osteoclastic activity, which is closely associated with inflammation. Benzydamine (BA) has been used as a cytokine-suppressive or non-steroidal anti-inflammatory drug that inhibits the production of pro-inflammatory cytokines or prostaglandins. However, its role in osteoclast differentiation and function remains unknown. Here, we explored the role of BA in regulating osteoclast differentiation and elucidated the underlying mechanism. BA inhibited osteoclast differentiation and strongly suppressed interleukin-1β (IL-1β) production. BA inhibited osteoclast formation and bone resorption when added to bone marrow-derived macrophages and differentiated osteoclasts, and the inhibitory effect was reversed by IL-1β treatment. The reporter assay and the inhibitor study of IL-1β transcription suggested that BA inhibited nuclear factor-κB and activator protein-1 by regulating IκB kinase, extracellular signal regulated kinase and P38, resulting in the down-regulation of IL-1β expression. BA also promoted osteoblast differentiation. Furthermore, BA protected lipopolysaccharide- and ovariectomy-induced bone loss in mice, suggesting therapeutic potential against inflammation-induced bone diseases and postmenopausal osteoporosis.

Enhancement of wound healing efficiency mediated by artificial dermis functionalized with EGF or NRG1

The use of artificial dermis as a skin substitute is a field of active study, as acellular dermal matrices from cadavers are susceptible to infection owing to their human origin. One such alternative dermal replacement scaffold, INSUREGRAF^®, is derived primarily from extracellular matrix proteins such as collagen and elastin and has been clinically used to treat severe skin wounds such as burns. This scaffold has proven to be useful to minimize wound contraction and scar formation owing to its biocompatibility, interconnected pore structure, sufficient biodegradability, and suitable mechanical properties. However, INSUREGRAF^® does not provide scar-free wound healing in cases of severe skin damage such as full-thickness (FT) excision. Considering that the efficient recruitment of fibroblasts and keratinocytes into a wound site represents a critical step in the regeneration of damaged skin, we attempted to enhance the efficiency for wound healing by fabricating growth factor-functionalized INSUREGRAF^®. In particular, we utilized epidermal growth factor (EGF) and an EGF family member, neuregulin-1 (NRG1), not previously studied in the context of wound healing, whose cellular role is to promote proliferation and migration in fibroblasts and keratinocytes. Both artificial dermis-growth factor combinations led to efficient recruitment of fibroblasts and keratinocytes into a wound site during the early steps of skin regeneration. Notably, EGF- or NRG1-functionalized INSUREGRAF^® induced rapid proliferation of skin cells in an ERK pathway-dependent manner and exhibited efficient wound healing in a Sprague-Dawley rat FT excision and grafting model. These results provide the foundation for expanding the use of growth factor-functionalized INSUREGRAF^® to clinical application in cases of severe skin injury.

Immediate Early Genes Anchor a Biological Pathway of Proteins Required for Memory Formation, Long-Term Depression and Risk for Schizophrenia

While the causes of myriad medical and infectious illnesses have been identified, the etiologies of neuropsychiatric illnesses remain elusive. This is due to two major obstacles. First, the risk for neuropsychiatric disorders, such as schizophrenia, is determined by both genetic and environmental factors. Second, numerous genes influence susceptibility for these illnesses. Genome-wide association studies have identified at least 108 genomic loci for schizophrenia, and more are expected to be published shortly. In addition, numerous biological processes contribute to the neuropathology underlying schizophrenia. These include immune dysfunction, synaptic and myelination deficits, vascular abnormalities, growth factor disruption, and N-methyl-D-aspartate receptor (NMDAR) hypofunction. However, the field of psychiatric genetics lacks a unifying model to explain how environment may interact with numerous genes to influence these various biological processes and cause schizophrenia. Here we describe a biological cascade of proteins that are activated in response to environmental stimuli such as stress, a schizophrenia risk factor. The central proteins in this pathway are critical mediators of memory formation and a particular form of hippocampal synaptic plasticity, long-term depression (LTD). Each of these proteins is also implicated in schizophrenia risk. In fact, the pathway includes four genes that map to the 108 loci associated with schizophrenia: GRIN2A, nuclear factor of activated T-cells (NFATc3), early growth response 1 (EGR1) and NGFI-A Binding Protein 2 (NAB2); each of which contains the "Index single nucleotide polymorphism (SNP)" (most SNP) at its respective locus. Environmental stimuli activate this biological pathway in neurons, resulting in induction of EGR immediate early genes: EGR1, EGR3 and NAB2. We hypothesize that dysfunction in any of the genes in this pathway disrupts the normal activation of Egrs in response to stress. This may result in insufficient electrophysiologic, immunologic, and neuroprotective, processes that these genes normally mediate. Continued adverse environmental experiences, over time, may thereby result in neuropathology that gives rise to the symptoms of schizophrenia. By combining multiple genes associated with schizophrenia susceptibility, in a functional cascade triggered by neuronal activity, the proposed biological pathway provides an explanation for both the polygenic and environmental influences that determine the complex etiology of this mental illness.

Erythropoietin Restores Long-Term Neurocognitive Function Involving Mechanisms of Neuronal Plasticity in a Model of Hyperoxia-Induced Preterm Brain Injury

Cerebral white and grey matter injury is the leading cause of an adverse neurodevelopmental outcome in prematurely born infants. High oxygen concentrations have been shown to contribute to the pathogenesis of neonatal brain damage. Here, we focused on motor-cognitive outcome up to the adolescent and adult age in an experimental model of preterm brain injury. In search of the putative mechanisms of action we evaluated oligodendrocyte degeneration, myelination, and modulation of synaptic plasticity-related molecules. A single dose of erythropoietin (20,000 IU/kg) at the onset of hyperoxia (24 hours, 80% oxygen) in 6-day-old Wistar rats improved long-lasting neurocognitive development up to the adolescent and adult stage. Analysis of white matter structures revealed a reduction of acute oligodendrocyte degeneration. However, erythropoietin did not influence hypomyelination occurring a few days after injury or long-term microstructural white matter abnormalities detected in adult animals. Erythropoietin administration reverted hyperoxia-induced reduction of neuronal plasticity-related mRNA expression up to four months after injury. Thus, our findings highlight the importance of erythropoietin as a neuroregenerative treatment option in neonatal brain injury, leading to improved memory function in adolescent and adult rats which may be linked to increased neuronal network connectivity.

Disruption of hippocampal neuregulin 1-ErbB4 signaling contributes to the hippocampus-dependent cognitive impairment induced by isoflurane in aged mice

BACKGROUND

A prolonged isoflurane exposure may lead to cognitive decline in rodents. Neuregulin 1 (NRG1)-ErbB4 signaling plays a key role in the modulation of hippocampal synaptic plasticity through regulating the neurotransmission. The authors hypothesized that hippocampal NRG1-ErbB4 signaling is involved in isoflurane-induced cognitive impairments in aged mice.

METHODS

Fourteen-month-old C57BL/6 mice were randomized to receive 100% O2 exposure, vehicle injection after 100% O2 exposure, vehicle injection after exposure to isoflurane carried by 100% O2, NRG1-β1 injection after exposure to isoflurane carried by 100% O2, and NRG1-β1 and an ErbB4 inhibitor AG1478 injection after exposure to isoflurane carried by 100% O2. Fear conditioning test was used to assess the cognitive function of mice 48-h postexposure. The brain tissues were harvested 48-h postexposure to determine the levels of NRG1, ErbB4, p-ErbB4, parvalbumin, and glutamic acid decarboxylase 67 in the hippocampus using Western blotting, enzyme-linked immunosorbent assay, and immunofluorescence.

RESULTS

The percentage of freezing time to context was decreased from 50.28 ± 11.53% to 30.82 ± 10.00%, and the hippocampal levels of NRG1, p-ErbB4/ErbB4, parvalbumin, and glutamic acid decarboxylase 67 were decreased from 172.79 ± 20.85 ng/g, 69.15 ± 12.20%, 101.68 ± 11.21%, and 104.71 ± 6.85% to 112.92 ± 16.65 ng/g, 42.26 ± 9.71%, 75.89 ± 10.26%, and 73.87 ± 16.89%, respectively, after isoflurane exposure. NRG1-β1 attenuated the isoflurane-induced hippocampus-dependent cognitive impairment and the declines in the hippocampal NRG1, p-ErbB4/ErbB4, parvalbumin, and glutamic acid decarboxylase 67. AG1478 inhibited the rescuing effects of NRG1-β1.

CONCLUSION

Disruption of NRG1-ErbB4 signaling in the parvalbumin-positive interneurons might, at least partially, contribute to the isoflurane-induced hippocampus-dependent cognitive impairment after exposure to isoflurane carried by 100% O2 in aged mice.

Downregulation of neuregulin 1-ErbB4 signaling in parvalbumin interneurons in the rat brain may contribute to the antidepressant properties of ketamine

Increasing evidence underscores the strong, rapid, and sustained antidepressant properties of ketamine with a good tolerability profile in patients with depression; however, the underlying mechanisms are not fully elucidated. Neuregulin 1 (NRG1) is a bipolar disorder susceptibility gene and a biomarker of major depressive disorder, which regulates pyramidal neuron activity via ErbB4 in parvalbumin interneurons. Moreover, NRG1-ErbB4 signaling is reported to play a key role in the modulation of synaptic plasticity through regulating the neurotransmission. We therefore hypothesized that hypofunction of NRG1-ErbB4 signaling in parvalbumin interneurons is involved in the process of ketamine exerting rapid antidepressant actions in rats subjected to the forced swimming test (FST). The results showed that ketamine reduced the immobility time and latency to feed of rats receiving the FST, downregulated the levels of NRG1, phosphorylated ErbB4 (p-ErbB4), parvalbumin, 67-kDA isoform of glutamic acid decarboxylase (GAD67), gamma-aminobutyric acid (GABA), and upregulated the levels of glutamate in the rat prefrontal cortex and hippocampus. Pretreatment with NRG1 abolished both ketamine's antidepressant effects and ketamine-induced reduction in p-ErbB4, parvalbumin, GAD67, and GABA levels and increase in glutamate levels. These results suggest that the downregulation of NRG1-ErbB4 signaling in parvalbumin interneurons in the rat brain may be a mechanism underlying ketamine's antidepressant properties.

Regulation of c-Fos gene expression by NF-κB: a p65 homodimer binding site in mouse embryonic fibroblasts but not human HEK293 cells

The immediate early gene c-Fos is reported to be regulated by Elk-1 and cAMP response element-binding protein (CREB), but whether nuclear factor (NF)-κB is also required for controlling c-Fos expression is unclear. In this study, we determined how NF-κB’s coordination with Elk/serum response factor (SRF) regulates c-fos transcription. We report that PMA strongly induced c-Fos expression, but tumor necrosis factor (TNF)-α did not. In mouse embryonic fibroblasts, the PMA induction of c-Fos was suppressed by a deficiency in IKKα, IKKβ, IKKγ, or p65. By contrast, in human embryonic kidney 293 cells, PMA induced c-Fos independently of p65. In accordance with these results, we identified an NF-κB binding site in the mouse but not human c-fos promoter. Under PMA stimulation, IKKα/β mediated p65 phosphorylation and the binding of the p65 homodimer to the NF-κB site in the mouse c-fos promoter. Furthermore, our studies demonstrated independent but coordinated functions of the IKKα/β-p65 and extracellular signal-regulated kinase (ERK)-Elk-1 pathways in the PMA induction of c-Fos. Collectively, these results reveal the distinct requirement of NF-κB for mouse and human c-fos regulation. Binding of the p65 homodimer to the κB site was indispensable for mouse c-fos expression, whereas the κB binding site was not present in the human c-fos promoter. Because of an inability to evoke sufficient ERK activation and Elk-1 phosphorylation, TNF-α induces c-Fos more weakly than PMA does in both mouse and human cells.

Neuregulin-1 suppresses cardiomyocyte apoptosis by activating PI3K/Akt and inhibiting mitochondrial permeability transition pore

Neuregulin-1 (NRG-1) has been shown to attenuate cardiomyocyte apoptosis but the underlying signaling mechanism remains elusive. In this study, we focused on mitochondrial permeability transition pore (mPTP) opening and PI3K/Akt pathway to investigate the effects of NRG-1 on oxidative stress-induced apoptosis of cardiomyocyte. Human cardiac myocytes and neonatal rat cardiac myocytes were exposed to hydrogen peroxide with or without pre-treatment with recombinant human neuregulin-1 (rhNRG-1). Cell apoptosis and mPTP opening were assayed by flow cytometry and confocal microscopy. The activation of Akt was detected by western blot analysis. The results showed that H(2)O(2) induced cardiomyocyte apoptosis and activated mPTP. rhNRG-1 inhibited mPTP and activated Akt in the presence of H(2)O(2) and further protected the cells from H(2)O(2)-induced apoptosis. However, rhNRG-1 failed to inhibit mPTP opening and cell apoptosis in the presence of PI3K inhibitor LY294002. Taken together, these findings suggest that NRG-1 activates PI3K/Akt signaling and inhibits mPTP opening, and downstream apoptotic events in cardiac myocytes subjected to oxidative stress.

Nociceptin is upregulated by FSH signaling in Sertoli cells in murine testes

In postnatal testes, follicle-stimulating hormone (FSH) acts on somatic Sertoli cells to activate gene expression directly via an intracellular signaling pathway composed of cAMP, cAMP-dependent protein kinase (PKA), and cAMP-response element-binding protein (CREB), and promotes germ cell development indirectly. Yet, the paracrine factors mediating the FSH effects to germ cells remained elusive. Here we show that nociceptin, known as a neuropeptide, is upregulated by FSH through cAMP/PKA/CREB pathway in Sertoli cells in murine testes. Chromatin immunoprecipitation from Sertoli cells shows that CREB phosphorylated at Ser133 associates with prepronociceptin gene encoding nociceptin. Analyses with Sertoli cells and testes demonstrates that both prepronociceptin mRNA and the nociceptin peptide are induced after FSH signaling is activated. In addition, the nociceptin peptide is induced in testes after 9days post partum following FSH surge. Thus, our findings may identify nociceptin as a novel paracrine mediator of the FSH effects in the regulation of spermatogenesis.

Effects of A-CREB, a dominant negative inhibitor of CREB, on the expression of c-fos and other immediate early genes in the rat SON during hyperosmotic stimulation in vivo

Intraperitoneal administration of hypertonic saline to the rat supraoptic nucleus (SON) increases the expression of several immediate early genes (IEG) and the vasopressin gene. These increases have usually been attributed to action of the cyclic-AMP Response Element Binding Protein (CREB). In this paper, we study the role of CREB in these events in vivo by delivering a potent dominant-negative form of CREB, known as A-CREB, to the rat SON through the use of an adeno-associated viral (AAV) vector. Preliminary experiments on HEK 293 cells in vitro showed that the A-CREB vector that we used completely eliminated CREB-induced c-fos expression. We stereotaxically injected this AAV-A-CREB into one SON and a control AAV into the contralateral SON of the same rat. Two weeks following these injections we injected hypertonic saline intraperitoneally into the rat. Using this paradigm, we could measure the relative effects of inhibiting CREB on the induced expression of c-fos, ngfi-a, ngfi-b, and vasopressin genes in the A-CREB AAV injected SON versus the control AAV injected SON in the same rat. We found only a small (20%) decrease of c-fos expression and a 30% decrease of ngfi-b expression in the presence of the A-CREB. There were no significant changes in expression found in the other IEGs nor in vasopressin that were produced by the A-CREB. This suggests that CREB may play only a minor role in the expression of IEGs and vasopressin in the osmotically activated SON in vivo.

Subchronic peripheral neuregulin-1 increases ventral hippocampal neurogenesis and induces antidepressant-like effects

Background

Adult hippocampal neurogenesis has been implicated in the mechanism of antidepressant action, and neurotrophic factors can mediate the neurogenic changes underlying these effects. The neurotrophic factor neuregulin-1 (NRG1) is involved in many aspects of brain development, from cell fate determination to neuronal maturation. However, nothing is known about the influence of NRG1 on neurodevelopmental processes occurring in the mature hippocampus.

Methods

Adult male mice were given subcutaneous NRG1 or saline to assess dentate gyrus proliferation and neurogenesis, as well as cell fate determination. Mice also underwent behavioral testing. Expression of ErbB3 and ErbB4 NRG1 receptors in newborn dentate gyrus cells was assessed at various time points between birth and maturity. The phenotype of ErbB-expressing progenitor cells was also characterized with cell type-specific markers.

Results

The current study shows that subchronic peripheral NRG1β administration selectively increased cell proliferation (by 71%) and neurogenesis (by 50%) in the caudal dentate gyrus within the ventral hippocampus. This pro-proliferative effect did not alter neuronal fate, and may have been mediated by ErbB3 receptors, which were expressed by newborn dentate gyrus cells from cell division to maturity and colocalized with SOX2 in the subgranular zone. Furthermore, four weeks after cessation of subchronic treatment, animals displayed robust antidepressant-like behavior in the absence of changes in locomotor activity, whereas acute treatment did not produce antidepressant effects.

Conclusions

These results show that neuregulin-1β has pro-proliferative, neurogenic and antidepressant properties, further highlight the importance of peripheral neurotrophic factors in neurogenesis and mood, and support the role of hippocampal neurogenesis in mediating antidepressant effects.

Neuregulins are essential for spermatogonial proliferation and meiotic initiation in neonatal mouse testis

The transition from mitosis to meiosis is unique to germ cells. In murine embryonic ovaries and juvenile testes, retinoic acid (RA) induces meiosis via the stimulated by retinoic acid gene 8 (Stra8), but its molecular pathway requires elucidation. We present genetic evidence in vivo and in vitro that neuregulins (NRGs) are essential for the proliferation of spermatogonia and the initiation of meiosis. Tamoxifen (TAM) was injected into 14-day post-partum (dpp) Sertoli cell-specific conditional Nrg1Ser–/– mutant mice. TAM induced testis degeneration, suppressed BrdU incorporation into spermatogonia and pre-leptotene primary spermatocytes, and decreased and increased the number of STRA8-positive and TUNEL-positive cells, respectively. In testicular organ cultures from 5-6 dpp wild-type mice and cultures of their re-aggregated spermatogonia and Sertoli cells, FSH, RA [all-trans-retinoic acid (ATRA), AM580, 9-cis-RA] and NRG1 promoted spermatogonial proliferation and meiotic initiation. However, TAM treatment of testicular organ cultures from the Nrg1Ser–/– mutants suppressed spermatogonial proliferation and meiotic initiation that was promoted by FSH or AM580. In re-aggregated cultures of purified spermatogonia, NRG1, NRG3, ATRA and 9-cis-RA promoted their proliferation and meiotic initiation, but neither AM580 nor FSH did. In addition, FSH, RAs and NRG1 promoted Nrg1 and Nrg3 mRNA expression in Sertoli cells. These results indicate that in juvenile testes RA and FSH induced meiosis indirectly through Sertoli cells when NRG1 and NRG3 were upregulated, as NRG1 amplified itself and NRG3. The amplified NRG1 and NRG3 directly induced meiosis in spermatogonia. In addition, ATRA and 9-cis-RA activated spermatogonia directly and promoted their proliferation and eventually meiotic initiation.