Neurotrophins in cell survival/death decisions

Morphogenetic theory of mental and cognitive disorders: the role of neurotrophic and guidance molecules

Mental illness and cognitive disorders represent a serious problem for the modern society. Many studies indicate that mental disorders are polygenic and that impaired brain development may lay the ground for their manifestation. Neural tissue development is a complex and multistage process that involves a large number of distant and contact molecules. In this review, we have considered the key steps of brain morphogenesis, and the major molecule families involved in these process. The review provides many indications of the important contribution of the brain development process and correct functioning of certain genes to human mental health. To our knowledge, this comprehensive review is one of the first in this field. We suppose that this review may be useful to novice researchers and clinicians wishing to navigate the field.

Nerve growth factor promotes differentiation and protects the oligodendrocyte precursor cells from in vitro hypoxia/ischemia

Introduction

Nerve growth factor (NGF) is a pleiotropic molecule acting on different cell types in physiological and pathological conditions. However, the effect of NGF on the survival, differentiation and maturation of oligodendrocyte precursor cells (OPCs) and oligodendrocytes (OLs), the cells responsible for myelin formation, turnover, and repair in the central nervous system (CNS), is still poorly understood and heavily debated.

Methods

Here we used mixed neural stem cell (NSC)-derived OPC/astrocyte cultures to clarify the role of NGF throughout the entire process of OL differentiation and investigate its putative role in OPC protection under pathological conditions.

Results

We first showed that the gene expression of all the neurotrophin receptors (TrkA, TrkB, TrkC, and p75^NTR ) dynamically changes during the differentiation. However, only TrkA and p75^NTR expression depends on T3-differentiation induction, as Ngf gene expression induction and protein secretion in the culture medium. Moreover, in the mixed culture, astrocytes are the main producer of NGF protein, and OPCs express both TrkA and p75^NTR . NGF treatment increases the percentage of mature OLs, while NGF blocking by neutralizing antibody and TRKA antagonist impairs OPC differentiation. Moreover, both NGF exposure and astrocyte-conditioned medium protect OPCs exposed to oxygenglucose deprivation (OGD) from cell death and NGF induces an increase of AKT/pAKT levels in OPCs nuclei by TRKA activation.

Discussion

This study demonstrated that NGF is implicated in OPC differentiation, maturation, and protection in the presence of metabolic challenges, also suggesting implications for the treatment of demyelinating lesions and diseases.

Epigenetic Regulation of NGF-Mediated Osteogenic Differentiation in Human Dental Mesenchymal Stem Cells

Nerve growth factor (NGF) is the best-characterized neurotrophin and is primarily recognized for its key role in the embryonic development of the nervous system and neuronal cell survival/differentiation. Recently, unexpected actions of NGF in bone regeneration have emerged as NGF is able to enhance the osteogenic differentiation of mesenchymal stem cells. However, little is known regarding how NGF signaling regulates osteogenic differentiation through epigenetic mechanisms. In this study, using human dental mesenchymal stem cells (DMSCs), we demonstrated that NGF mediates osteogenic differentiation through p75NTR, a low-affinity NGF receptor. P75NTR-mediated NGF signaling activates the JNK cascade and the expression of KDM4B, an activating histone demethylase, by removing repressive H3K9me3 epigenetic marks. Mechanistically, NGF-activated c-Jun binds to the KDM4B promoter region and directly upregulates KDM4B expression. Subsequently, KDM4B directly and epigenetically activates DLX5, a master osteogenic gene, by demethylating H3K9me3 marks. Furthermore, we revealed that KDM4B and c-Jun from the JNK signaling pathway work in concert to regulate NGF-mediated osteogenic differentiation through simultaneous recruitment to the promoter region of DLX5. We identified KDM4B as a key epigenetic regulator during the NGF-mediated osteogenesis both in vitro and in vivo using the calvarial defect regeneration mouse model. In conclusion, our study thoroughly elucidated the molecular and epigenetic mechanisms during NGF-mediated osteogenesis.

Cell Surface Proteins for Enrichment and In Vitro Characterization of Human Pluripotent Stem Cell-Derived Myogenic Progenitors

Human myogenic progenitors can be derived from pluripotent stem cells (PSCs) for use in modeling natural and pathological myogenesis, as well as treating muscle diseases. Transgene-free methods of deriving myogenic progenitors from different PSC lines often produce mixed populations that are heterogeneous in myogenic differentiation potential, yet detailed and accurate characterization of human PSC-derived myogenic progenitors remains elusive in the field. The isolation and purification of human PSC-derived myogenic progenitors is thus an important methodological consideration when we investigate the properties and behaviors of these cells in culture. We previously reported a transgene-free, serum-free floating sphere culture method for the derivation of myogenic progenitors from human PSCs. In this study, we first performed comprehensive cell surface protein profiling of the sphere culture cells through the screening of 255 antibodies. Next, we used magnetic activated cell sorting and enriched the cells according to the expression of specific surface markers. The ability of muscle differentiation in the resulting cells was characterized by immunofluorescent labeling and quantification of positively stained cells. Our results revealed that myotube-forming cells resided in the differentiated cultures of CD29+, CD56+, CD271+, and CD15– fractions, while thick and multinucleated myotubes were identified in the differentiated cultures from CD9+ and CD146+ fractions. We found that PAX7 localization to the nucleus correlates with myotube-forming ability in these sorted populations. We also demonstrated that cells in unsorted, CD271+, and CD15– fractions responded differently to cryopreservation and prolonged culture expansion. Lastly, we showed that CD271 expression is essential for terminal differentiation of human PSC-derived myogenic progenitors. Taken together, these cell surface proteins are not only useful markers to identify unique cellular populations in human PSC-derived myogenic progenitors but also functionally important molecules that can provide valuable insight into human myogenesis.

Head and neck cancer management and cancer stem cells implication

Head and neck squamous cell carcinomas (HNSCCs) arise in the mucosal linings of the upper aerodigestive tract and are heterogeneous in nature. Risk factors for HNSCCs are smoking, excessive alcohol consumption, and the human papilloma virus. Conventional treatments are surgery, radiotherapy, chemotherapy, or a combined modality; however, no international standard mode of therapy exists. In contrast to the conventional model of clonal evolution in tumor development, there is a newly proposed theory based on the activity of cancer stem cells (CSCs) as the model for carcinogenesis. This “CSC hypothesis” may explain the high mortality rate, low response to treatments, and tendency to develop multiple tumors for HNSCC patients. We review current knowledge on HNSCC etiology and treatment, with a focus on CSCs, including their origins, identifications, and effects on therapeutic options.

Identification of Neural Stem Cells from Postnatal Mouse Auditory Cortex In Vitro

Auditory signals are processed in multiple central nervous system structures, including the auditory cortex (AC). Development of stem cell biology provides the opportunity to identify neural stem cells (NSCs) in the central nervous system. However, it is unclear whether NSCs exist in the AC. The aim of this study is to determine the existence of NSCs in the postnatal mouse AC. To accomplish this aim, postnatal mouse AC tissues were dissected and dissociated into singular cells and small cell clumps, which were suspended in the culture medium to observe neurosphere formation. The spheres were examined by quantitative real-time polymerase chain reaction and immunofluorescence to determine expression of NSC genes and proteins. In addition, AC-spheres were cultured in the presence or absence of astrocyte-conditioned medium (ACM) to study neural differentiation. The results show that AC-derived cells were able to proliferate to form neurospheres, which expressed multiple NSC genes and proteins, including SOX2 and NESTIN. AC-derived NSCs (AC-NSCs) differentiated into cells expressing neuronal and glial cell markers. However, the neuronal generation rate is low in the culture medium containing nerve growth factor, ∼8%. To stimulate neuronal generation, AC-NSCs were cultured in the culture medium containing ACM. In the presence of ACM, ∼29% AC-NSCs differentiated into cells expressing neuronal marker class III β-tubulin (TUJ1). It was observed that the length of neurites of AC-NSC-derived neurons in the ACM group was significantly longer than that of the control group. In addition, synaptic protein immunostaining showed significantly higher expression of synaptic proteins in the ACM group. These results suggest that ACM is able to stimulate neuronal differentiation, extension of neurites, and expression of synaptic proteins. Identifying AC-NSCs and determining effects of ACM on NSC differentiation will be important for the auditory research and other neural systems.

Assessment of Neurotrophins and Inflammatory Mediators in Vitreous of Patients With Diabetic Retinopathy

Purpose

To assess vitreous levels of inflammatory cytokines and neurotrophins (NTs) in diabetic retinopathy (DR) and elucidate their potential roles.

Methods

A prospective study was performed on 50 vitreous samples obtained from patients with DR (n = 22) and the nondiabetic controls (n = 28). All patients were candidates for vitrectomy. Inflammatory cytokine and NT levels were determined with ELISA. Potential source and role of NTs was determined by using human retinal Müller glia and mouse photoreceptor cells and challenging them with TNF-α or IL-1β, followed by detection of NTs and cell death.

Results

Vitreous NT levels of all DR patients were significantly higher than those of nondiabetic controls (nerve growth factor [NGF, P = 0.0001], brain-derived neurotrophic factor [BDNF, P = 0.009], neurotrophin-3 [NT-3, P < 0.0001], neurotrophin-4 [NT-4, P = 0.0001], ciliary neurotrophic factor [CNTF, P = 0.0001], and glial cell–derived neurotrophic factor [GDNF, P = 0.008]). Similarly, the levels of inflammatory mediators IL-1β (P < 0.0001), IL-6 (P = 0.0005), IL-8 (P < 0.0001), and TNF-α (P < 0.0001) were also higher in eyes with DR. Interestingly, inflammatory cytokine and NT levels, particularly TNF-α (P < 0.05), IL-8 (P < 0.004), NT-3 (P = 0.012), NGF (P = 0.04), GDNF (P = 0.005), and CNTF (P = 0.002), were higher in eyes with nonproliferative diabetic retinopathy (NPDR) than in eyes with active proliferative diabetic retinopathy (PDR). Cytokine stimulation of Müller glia resulted in production of NTs, and GDNF treatment reduced photoreceptor cell death in response to inflammation and oxidative stress.

Conclusions

Together, our study demonstrated that patients with DR have higher levels of both inflammatory cytokines and NTs in their vitreous. Müller glia could be the potential source of NTs under inflammatory conditions to exert neuroprotection.

Blocking Nerve Growth Factor Signaling Reduces the Neural Invasion Potential of Pancreatic Cancer Cells

Perineural invasion (PNI) is thought to be one of the factors responsible for the high rate of tumor recurrence after surgery and the pain generation associated with pancreatic cancer. Signaling via the nerve growth factor (NGF) pathway between pancreatic cancer cells and the surrounding nerves has been implicated in PNI, and increased levels of these proteins have been correlated to poor prognosis. In this study, we examine the molecular mechanism of the NGF signaling pathway in PNI in pancreatic cancer. We show that knocking down NGF or its receptors, TRKA and p75NTR, or treatment with GW441756, a TRKA kinase inhibitor, reduces the proliferation and migration of pancreatic cancer cells in vitro. Furthermore, pancreatic cancer cells migrate towards dorsal root ganglia (DRG) in a co-culture assay, indicating a paracrine NGF signaling between the DRGs and pancreatic cancer cells. Knocking down the expression of NGF pathway proteins or inhibiting the activity of TRKA by GW441756 reduced the migratory ability of Mia PaCa2 towards the DRGs. Finally, blocking NGF signaling by NGF neutralizing antibodies or GW441756 inhibited the neurite formation in PC-12 cells in response to conditioned media from pancreatic cancer cells, indicating a reciprocal signaling pathway between the pancreatic cancer cells and nerves. Our results indicate that NGF signaling pathway provides a potential target for developing molecularly targeted therapies to decrease PNI and reduce pain generation. Since there are several TRKA antagonists currently in early clinical trials they could now be tested in the clinical situation of pancreatic cancer induced pain.

Long Non-coding RNA in Neurons: New Players in Early Response to BDNF Stimulation

Brain-derived neurotrophic factor (BDNF) is a neurotrophin family member that is highly expressed and widely distributed in the brain. BDNF is critical for neural survival and plasticity both during development and in adulthood, and dysfunction in its signaling may contribute to a number of neurodegenerative disorders. Deep understanding of the BDNF-activated molecular cascade may thus help to find new biomarkers and therapeutic targets. One interesting direction is related to the early phase of BDNF-dependent gene expression regulation, which is responsible for the activation of selective gene programs that lead to stable functional and structural remodeling of neurons. Immediate-early coding genes activated by BDNF are under investigation, but the involvement of the non-coding RNAs is largely unexplored, especially the long non-coding RNAs (lncRNAs). lncRNAs are emerging as key regulators that can orchestrate different aspects of nervous system development, homeostasis, and plasticity, making them attractive candidate markers and therapeutic targets for brain diseases. We used microarray technology to identify differentially expressed lncRNAs in the immediate response phase of BDNF stimulation in a neuronal cell model. Our observations on the putative functional role of lncRNAs provide clues to their involvement as master regulators of gene expression cascade triggered by BDNF.

Ischemic regulation of brain-derived neurotrophic factor-mediated cell volume and TrkB expression in glial (Müller) and bipolar cells of the rat retina

BACKGROUND

Osmotic swelling of neurons and glial cells contributes to retinal edema and neurodegeneration. BDNF, a major neuroprotectant in the retina, was shown to inhibit osmotic swelling of glial (Müller) and bipolar cells in the rat retina; the effect of BDNF on the bipolar cell swelling is mediated by inducing a release of neuroprotective cytokines from Müller cells (Berk et al., Neuroscience 295:175-186, 2015). We determined whether BDNF-mediated cell volume regulation was altered after transient retinal ischemia.

METHODS

Retinal slices from the eyes of rats that underwent a 1-h pressure-induced retinal ischemia and from control eyes were superfused with a hypoosmotic solution.

RESULTS

Exogenous BDNF prevented osmotic swelling of Müller cells in both control and post-ischemic retinal slices. BDNF also prevented osmotic swelling of bipolar cells in the control retina, but not in the ischemic retina. On the other hand, exogenous bFGF prevented the swelling of both Müller and bipolar cells in the ischemic retina. Freshly isolated Müller cells of control retinas displayed immunoreactivity of truncated but not full-length TrkB. In contrast, Müller cells of post-ischemic retinas displayed immunoreactivity of both TrkB isoforms. Bipolar cells isolated from control and post-ischemic retinas were immunolabeled for both TrkB isoforms.

CONCLUSIONS

The data may suggest that the ischemic abrogation of the BDNF effect in bipolar cells is related to altered BDNF receptor expression in Müller cells. Glial upregulation of full-length TrkB may support the survival of Müller cells in the ischemic retina, but may impair the BDNF-induced release of neuroprotective cytokines such as bFGF from Müller cells.

Retinoic acid-induced CHD5 upregulation and neuronal differentiation of neuroblastoma

Background

Chromodomain-helicase DNA binding protein 5 (CHD5) is an important tumor suppressor gene deleted from 1p36.31 in neuroblastomas (NBs). High CHD5 expression is associated with a favorable prognosis, but deletion or low expression is frequent in high-risk tumors. We explored the role of CHD5 expression in the neuronal differentiation of NB cell lines.

Methods

NB cell lines SH-SY5Y (SY5Y), NGP, SK-N-DZ, IMR5, LAN5, SK-N-FI, NB69 and SH-EP were treated with 1–10 μM 13-cis-retinoic acid (13cRA) for 3–12 days. qRT-PCR and Western blot analyses were performed to measure mRNA and protein expression levels, respectively. Morphological differences were examined by both phase contrast and immunofluorescence studies.

Results

Treatment of SY5Y cells with 13cRA caused upregulation of CHD5 expression in a time- and dose-dependent manner (1, 5, or 10 μM for 7 or 12 days) and also induced neuronal differentiation. Furthermore, both NGP and SK-N-DZ cells showed CHD5 upregulation and neuronal differentiation after 13cRA treatment. In contrast, 13cRA treatment of IMR5, LAN5, or SK-N-FI induced neither CHD5 expression nor neuronal differentiation. NB69 cells showed two different morphologies (neuronal and substrate adherent) after 12 days treatment with 10 μM of 13cRA. CHD5 expression was high in the neuronal cells, but low/absent in the flat, substrate adherent cells. Finally, NGF treatment caused upregulation of CHD5 expression and neuronal differentiation in SY5Y cells transfected to express TrkA (SY5Y-TrkA) but not in TrkA-null parental SY5Y cells, and both changes were blocked by a pan-TRK inhibitor.

Conclusions

Treatment with 13cRA induces neuronal differentiation only in NB cells that upregulate CHD5. In addition, NGF induced CHD5 upregulation and neuronal differentiation only in TrkA expressing cells. Together, these results suggest that CHD5 is downstream of TrkA, and CHD5 expression may be crucial for neuronal differentiation induced by either 13cRA or TrkA/NGF signaling.

Electronic supplementary material

The online version of this article (doi:10.1186/s12943-015-0425-y) contains supplementary material, which is available to authorized users.

Potential Effect of CD271 on Human Mesenchymal Stromal Cell Proliferation and Differentiation

The Low-Affinity Nerve Growth Factor Receptor (LNGFR), also known as CD271, is a member of the tumor necrosis factor receptor superfamily. The CD271 cell surface marker defines a subset of multipotential mesenchymal stromal cells and may be used to isolate and enrich cells derived from bone marrow aspirate. In this study, we compare the proliferative and differentiation potentials of CD271+ and CD271- mesenchymal stromal cells. Mesenchymal stromal cells were isolated from bone marrow aspirate and adipose tissue by plastic adherence and positive selection. The proliferation and differentiation potentials of CD271+ and CD271- mesenchymal stromal cells were assessed by inducing osteogenic, adipogenic and chondrogenic in vitro differentiation. Compared to CD271+, CD271- mesenchymal stromal cells showed a lower proliferation rate and a decreased ability to give rise to osteocytes, adipocytes and chondrocytes. Furthermore, we observed that CD271+ mesenchymal stromal cells isolated from adipose tissue displayed a higher efficiency of proliferation and trilineage differentiation compared to CD271+ mesenchymal stromal cells isolated from bone marrow samples, although the CD271 expression levels were comparable. In conclusion, these data show that both the presence of CD271 antigen and the source of mesenchymal stromal cells represent important factors in determining the ability of the cells to proliferate and differentiate.

CD271 is a functional and targetable marker of tumor-initiating cells in head and neck squamous cell carcinoma

Tumor-initiating cells (TICs) in squamous cell carcinoma of the head and neck (SCCHN) are best characterized by their surface expression of CD44. Although there is great interest in identifying strategies to target this population, no marker of these cells has been found to be functionally active. Here, we examined the expression of the purported marker of normal human oral epithelial stem cells, CD271. We show that CD271 expression is restricted to a subset of the CD44⁺ cells. Using xenograft assays, we show that the CD44⁺CD271⁺ subpopulation contains the most tumorigenic cells. Loss of CD271 function results in a block in the G2-M phase of the cell cycle and a profound negative impact on the capacity of these cells to initiate tumor formation in vivo. Incubation with recombinant NGF results in enhanced phosphorylation of Erk, providing additional evidence that CD271 is functionally active. Finally, incubation of SCCHN cells with antibody to CD271 results in decreased Erk phosphorylation and decreased tumor formation in vivo. Thus, our data are the first to demonstrate that CD271 more specifically identifies the TIC subpopulation within the CD44⁺ compartment in SCCHN and that this receptor is a functionally active and targetable molecule.

p75NTR is highly expressed in vestibular schwannomas and promotes cell survival by activating nuclear transcription factor κB

Vestibular schwannomas (VSs) arise from Schwann cells (SCs) and result from the loss of function of merlin, the protein product of the NF2 tumor suppressor gene. In contrast to non-neoplastic SCs, VS cells survive long-term in the absence of axons. We find that p75(NTR) is overexpressed in VSs compared with normal nerves, both at the transcript and protein level, similar to the response of non-neoplastic SCs following axotomy. Despite elevated p75(NTR) expression, VS cells are resistant to apoptosis due to treatment with proNGF, a high affinity ligand for p75(NTR) . Furthermore, treatment with proNGF protects VS cells from apoptosis due to c-Jun N-terminal kinase (JNK) inhibition indicating that p75(NTR) promotes VS cell survival. Treatment of VS cells with proNGF activated NF-κB while inhibition of JNK with SP600125 or siRNA-mediated knockdown reduced NF-κB activity. Significantly, proNGF also activated NF-κB in cultures treated with JNK inhibitors. Thus, JNK activity appears to be required for basal levels of NF-κB activity but not for proNGF-induced NF-κB activity. To confirm that the increase in NF-κB activity contributes to the prosurvival effect of proNGF, we infected VS cultures with Ad.IκB.SerS32/36A virus, which inhibits NF-κB activation. Compared with control virus, Ad.IκB.SerS32/36A significantly increased apoptosis including in VS cells treated with proNGF. Thus, in contrast to non-neoplastic SCs, p75(NTR) signaling provides a prosurvival response in VS cells by activating NF-κB independent of JNK. Such differences may contribute to the ability of VS cells to survive long-term in the absence of axons.

Quantitative temporal viromics: an approach to investigate host-pathogen interaction

A systematic quantitative analysis of temporal changes in host and viral proteins throughout the course of a productive infection could provide dynamic insights into virus-host interaction. We developed a proteomic technique called “quantitative temporal viromics” (QTV), which employs multiplexed tandem-mass-tag-based mass spectrometry. Human cytomegalovirus (HCMV) is not only an important pathogen but a paradigm of viral immune evasion. QTV detailed how HCMV orchestrates the expression of >8,000 cellular proteins, including 1,200 cell-surface proteins to manipulate signaling pathways and counterintrinsic, innate, and adaptive immune defenses. QTV predicted natural killer and T cell ligands, as well as 29 viral proteins present at the cell surface, potential therapeutic targets. Temporal profiles of >80% of HCMV canonical genes and 14 noncanonical HCMV open reading frames were defined. QTV is a powerful method that can yield important insights into viral infection and is applicable to any virus with a robust in vitro model.

PaperClip

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>8,000 proteins quantified over eight time points, including 1,200 cell-surface proteins

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Temporal profiles of 139/171 canonical HCMV proteins and 14 noncanonical HCMV ORFs

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Multiple families of cell-surface receptors selectively modulated by HCMV

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Multiple signaling pathways modulated during HCMV infection

Retinoic acid induced-1 (Rai1) regulates craniofacial and brain development in Xenopus

Retinoic acid induced-1 (RAI1) is an important yet understudied histone code reader that when mutated in humans results in Smith-Magenis syndrome (SMS), a neurobehavioral disorder accompanied by signature craniofacial abnormalities. Despite previous studies in mouse and human cell models, very little is known about the function of RAI1 during embryonic development. In the present study, we have turned to the model vertebrates Xenopus laevis and Xenopus tropicalis to better understand the developmental roles of Rai1. First we demonstrate that the Rai1 protein sequence is conserved in frogs, especially in known functional domains. By in situ hybridization we revealed expression of rai1 in the developing craniofacial tissues and the nervous system. Knockdown of Rai1 using antisense morpholinos resulted in defects in the developing brain and face. In particular, Rai1 morphants display midface hypoplasia and malformed mouth shape analogous to defects in humans with SMS. These craniofacial defects were accompanied with aberrant neural crest migration and reduction in the size of facial cartilage elements. Rai1 morphants also had defects in axon patterns and decreased forebrain ventricle size. Such brain defects correlated with a decrease in the neurotrophic factor, bdnf, and increased forebrain apoptosis. Our results emphasize a critical role of Rai1 for normal neural and craniofacial development, and further the current understanding of potential mechanisms that cause SMS.

Complexity of trophic factor signaling in experimental autoimmune encephalomyelitis: differential expression of neurotrophic and gliotrophic factors

Soluble factors that promote survival and differentiation of glia and neurons during development are likely to play key roles in neurodegeneration and demyelinating diseases such as multiple sclerosis (MS) and have the potential to be important therapeutic targets. We examined the effect of TrkB signaling and the expression patterns of neurotrophic and gliotrophic factors in the mouse brain in MOG-induced experimental allergic encephalomyelitis (EAE). With induction of mild disease, TrkB heterozygous mice were more severely affected compared to their wild type littermates. However, with more potent disease induction, TrkB heterozygotes fared similar to their wild type littermates, suggesting complex modulatory roles for TrkB signaling. One possible explanation for this difference is that the expression patterns of neurotrophic factors correlate with disease severity in individual mice with mild disease, but not in more severe disease. With the less potent induction in C57BL/6 mice, we found that BDNF was consistently increased at EAE onset, while the soluble gliotrophic factor neuregulin (NRG1) was increased only in the chronic phase of the disease. Treatment of these animals with glatiramer acetate (GA) to decrease disease severity resulted in lower levels of both BDNF and NRG1 expression in some mice at 35days after immunization compared to those in untreated EAE mice, but had no direct effect on these factors in the absence of EAE. Our results suggest a complex interplay between neurotrophic and gliotrophic factors in EAE that is dependent on disease stage and severity. While signaling by BDNF through TrkB is protective in mild disease, this effect was not seen in more severe disease. The late induction of NRG1 in the chronic stage of disease could also worsen disease severity through its known ability to activate microglial, inflammatory pathways. While complex, these studies begin to define underlying axoglial trophic activities that are likely involved in both disease pathogenesis and repair.

Brain-derived neurotrophic factor-estrogen interactions in the hippocampal mossy fiber pathway: implications for normal brain function and disease

The neurotrophin brain-derived neurotrophic factor (BDNF) and the steroid hormone estrogen exhibit potent effects on hippocampal neurons during development and in adulthood. BDNF and estrogen have also been implicated in the etiology of diverse types of neurological disorders or psychiatric illnesses, or have been discussed as potentially important in treatment. Although both are typically studied independently, it has been suggested that BDNF mediates several of the effects of estrogen in the hippocampus, and that these interactions play a role in the normal brain as well as disease. Here we focus on the mossy fiber (MF) pathway of the hippocampus, a critical pathway in normal hippocampal function, and a prime example of a location where numerous studies support an interaction between BDNF and estrogen in the rodent brain. We first review the temporal and spatially regulated expression of BDNF and estrogen in the MFs, as well as their receptors. Then we consider the results of studies that suggest that 17β-estradiol alters hippocampal function by its influence on BDNF expression in the MF pathway. We also address the hypothesis that estrogen influences the hippocampus by mechanisms related not only to the mature form of BDNF, acting at trkB receptors, but also by regulating the precursor, proBDNF, acting at p75NTR. We suggest that the interactions between BDNF and 17β-estradiol in the MFs are potentially important in the normal function of the hippocampus, and have implications for sex differences in functions that depend on the MFs and in diseases where MF plasticity has been suggested to play an important role, Alzheimer's disease, epilepsy and addiction.

Spatial segregation of BDNF transcripts enables BDNF to differentially shape distinct dendritic compartments

BDNF is produced from many transcripts that display distinct subcellular localization, suggesting that spatially restricted effects occur as a function of genetic and physiological regulation. Different BDNF 5' splice variants give a restricted localization in the cell body or the proximal and distal compartments of dendrites; however, the functional consequences are not known. Silencing individual endogenous transcripts or overexpressing BDNF-GFP transcripts in cultured neurons demonstrated that whereas some transcripts (1 and 4) selectively affected proximal dendrites, others (2C and 6) affected distal dendrites. Moreover, segregation of BDNF transcripts resulted in a highly selective activation of the BDNF TrkB receptor. These studies indicate that spatial segregation of BDNF transcripts enables BDNF to differentially shape distinct dendritic compartments.

Postlesion estradiol treatment increases cortical cholinergic innervations via estrogen receptor-α dependent nonclassical estrogen signaling in vivo

17β-Estradiol (E2) treatment exerts rapid, nonclassical actions via intracellular signal transduction system in basal forebrain cholinergic (BFC) neurons in vivo. Here we examined the effect of E2 treatment on lesioned BFC neurons in ovariectomized mice and the role of E2-induced nonclassical action in this treatment. Mice given an N-methyl-d-aspartic acid (NMDA) injection into the substantia innominata-nucleus basalis magnocellularis complex (SI-NBM) exhibited cholinergic cell loss in the SI-NBM and ipsilateral cholinergic fiber loss in the cortex. A single injection of E2 after NMDA lesion did not have an effect on cholinergic cell loss in the SI-NBM, but it restored the ipsilateral cholinergic fiber density in the cortex in a time- and dose-dependent manner. The most effective cholinergic fiber restoration was observed with 33 ng/g E2 treatment at 1 h after NMDA lesion. The E2-induced cholinergic fiber restoration was absent in neuron-specific estrogen receptor-α knockout mice in vivo. Selective activation of nonclassical estrogen signaling in vivo by estren induced E2-like restorative actions. Selective blockade of the MAPK or protein kinase A pathway in vivo prevented E2's ability to restore cholinergic fiber loss. Finally, studies in intact female mice revealed an E2-induced restorative effect that was similar to that of E2-treated ovariectomized mice. These observations demonstrate that a single E2 treatment restores the BFC fiber loss in the cortex, regardless of endogenous E2 levels. They also reveal the critical role of nonclassical estrogen signaling via estrogen receptor-α and protein kinase A-MAPK pathways in E2-induced restorative action in the cholinergic system in vivo.

Activation of ADF/cofilin mediates attractive growth cone turning toward nerve growth factor and netrin-1

Proper neural circuitry requires that growth cones, motile tips of extending axons, respond to molecular guidance cues expressed in the developing organism. However, it is unclear how guidance cues modify the cytoskeleton to guide growth cone pathfinding. Here, we show acute treatment with two attractive guidance cues, nerve growth factor (NGF) and netrin-1, for embryonic dorsal root ganglion and temporal retinal neurons, respectively, results in increased growth cone membrane protrusion, actin polymerization, and filamentous actin (F-actin). ADF/cofilin (AC) family proteins facilitate F-actin dynamics, and we found the inactive phosphorylated form of AC is decreased in NGF- or netrin-1-treated growth cones. Directly increasing AC activity mimics addition of NGF or netrin-1 to increase growth cone protrusion and F-actin levels. Extracellular gradients of NGF, netrin-1, and a cell-permeable AC elicit attractive growth cone turning and increased F-actin barbed ends, F-actin accumulation, and active AC in growth cone regions proximal to the gradient source. Reducing AC activity blunts turning responses to NGF and netrin. Our results suggest that gradients of NGF and netrin-1 locally activate AC to promote actin polymerization and subsequent growth cone turning toward the side containing higher AC activity.

Acute stress alters transcript expression pattern and reduces processing of proBDNF to mature BDNF in Dicentrarchus labrax

BACKGROUND

Stress involves alterations of brain functioning that may precipitate to mood disorders. The neurotrophin Brain Derived Neurotrophic Factor (BDNF) has recently been involved in stress-induced adaptation. BDNF is a key regulator of neuronal plasticity and adaptive processes. Regulation of BDNF is complex and may reflect not only stress-specific mechanisms but also hormonal and emotional responses. For this reason we used, as an animal model of stress, a fish whose brain organization is very similar to that of higher vertebrates, but is generally considered free of emotional reactions.

RESULTS

We provide a comprehensive characterization of BDNF gene in the Dicentrarchus labrax and its transcriptional, translational and post-translational regulation following acute stress. While total BDNF mRNA levels are unchanged, BDNF transcripts 1c and 1d resulted down regulated after acute stress. Acute stress induces also a significant increase in proBDNF levels and reduction in mature BDNF suggesting altered regulation of proBDNF proteolytic processing. Notably, we provide here the first evidence that fishes possess a simplified proteolytic regulation of BDNF since the pro28Kda form, generated by the SKI-1 protease in mammals, is absent in fishes because the cleavage site has first emerged in reptilians. Finally, we show that the proBDNF/totBDNF ratio is a highly predictive novel quantitative biomarker to detect stress in fishes with sensitivity = 100%, specificity = 87%, and Negative Predictive Value = 100%.

CONCLUSION

The high predictivity of proBDNF/totBDNF ratio for stress in lower vertebrates indicates that processing of BDNF is a central mechanism in adaptation to stress and predicts that a similar regulation of pro/mature BDNF has likely been conserved throughout evolution of vertebrates from fish to man.

Genetics and genomics of neuroblastoma

Neuroblastoma is a pediatric cancer of the developing sympathetic nervous system that most often affects young children. It remains an important pediatric problem because it accounts for approximately 15% of childhood cancer mortality. The disease is clinically heterogeneous, with the likelihood of cure varying greatly according to age at diagnosis, extent of disease, and tumor biology. This extreme clinical heterogeneity reflects the complexity of genetic and genomic events associated with development and progression of disease. Inherited genetic variants and mutations that initiate tumorigenesis have been identified in neuroblastoma and multiple somatically acquired genomic alterations have been described that are relevant to disease progression. This chapter focuses on recent genome-wide studies that have utilized high-density single nucleotide polymorphism (SNP) genotyping arrays to discover genetic factors predisposing to tumor initiation such as rare mutations at locus 2p23 (in ALK gene) for familial neuroblastoma, common SNPs at 6p22 (FLJ22536 and FLJ44180) and 2q35 (BARD1), and a copy number polymorphism at 1q21.1 (NBPF23) for sporadic neuroblastoma. It also deals with well known and recently reported somatic changes in the tumor genome such as mutations, gain of alleles and activation of oncogenes, loss of alleles, or changes in tumor-cell ploidy leading to the diverse clinical behavior of neuroblastomas. Finally, this chapter reviews gene expression profiles of neuroblastoma associated with pathways of the signaling of neurotrophins and apoptotic factors that could have a role in neuroblastoma development and progression. Looking forward, a major challenge will be to understand how inherited genetic variation and acquired somatic alterations in the tumor genome interact to exact phenotypic differences in neuroblastoma, and cancer in general.

Necdin and TrkA contribute to modulation by p75NTR of resistance to oxidant stress

The neurotrophin receptor p75NTR provides protection from oxidant stress induced by 6-hydroxydopamine (6-OHDA) and resultant cell death. In the absence of p75NTR, TrkA is upregulated and its signaling pathway effectors are increasingly activated. Necdin, a MAGE protein and known interactor of p75NTR and TrkA, is a potential mediator of this phenomenon. Decreased expression of necdin protein in p75NTR-deficient PC12 cells decreased TrkA expression and increased PC12 cell resistance to 6-OHDA. Inhibition of JNK phosphorylation by SP600125 also resulted in increased resistance to 6-OHDA, suggesting that TrkA signaling underlies the susceptibility of these cells to oxidant stress.

Cellular signaling and factors involved in Müller cell gliosis: neuroprotective and detrimental effects

Müller cells are active players in normal retinal function and in virtually all forms of retinal injury and disease. Reactive Müller cells protect the tissue from further damage and preserve tissue function by the release of antioxidants and neurotrophic factors, and may contribute to retinal regeneration by the generation of neural progenitor/stem cells. However, Müller cell gliosis can also contribute to neurodegeneration and impedes regenerative processes in the retinal tissue by the formation of glial scars. This article provides an overview of the neuroprotective and detrimental effects of Müller cell gliosis, with accounts on the cellular signal transduction mechanisms and factors which are implicated in Müller cell-mediated neuroprotection, immunomodulation, regulation of Müller cell proliferation, upregulation of intermediate filaments, glial scar formation, and the generation of neural progenitor/stem cells. A proper understanding of the signaling mechanisms implicated in gliotic alterations of Müller cells is essential for the development of efficient therapeutic strategies that increase the supportive/protective and decrease the destructive roles of gliosis.

Thyroid hormone and cerebellar development

Thyroid hormone (TH) plays a key role in mammalian brain development. The developing brain is sensitive to both TH deficiency and excess. Brain development in the absence of TH results in motor skill deficiencies and reduced intellectual development. These functional abnormalities can be attributed to maldevelopment of specific cell types and regions of the brain including the cerebellum. TH functions at the molecular level by regulating gene transcription. Therefore, understanding how TH regulates cerebellar development requires identification of TH-regulated gene targets and the cells expressing these genes. Additionally, the process of TH-dependent regulation of gene expression is tightly controlled by mechanisms including regulation of TH transport, TH metabolism, toxicologic inhibition of TH signaling, and control of the nuclear TH response apparatus. This review will describe the functional, cellular, and molecular effects of TH deficit in the developing cerebellum and emphasize the most recent findings regarding TH action in this important brain region.

BDNF splice variants from the second promoter cluster support cell survival of differentiated neuroblastoma upon cytotoxic stress

The neurotrophin brain-derived neurotrophic factor (BDNF) is a key survival factor for neural cells. In particular, in neuroblastoma tumour cells, expression of the BDNF/TrkB autocrine signalling system promotes a more malignant phenotype and resistance to chemotherapy. The human BDNF gene contains two clusters of upstream exons encoding the 5′UTR (exon 1 to exon 3 and exon 4 to exon 9a), these are alternatively spliced to a common exon 9, which contains the coding region and the 3′UTR. At least 34 different BDNF mRNA transcripts can be generated, although their physiological role is still unknown. The purpose of this study is to determine which BDNF transcript is involved in cell survival of the human neuroblastoma cell lines SH-SY-5Y (single-copy MYCN) and SK-N-BE (amplified MYCN). Expression of human BDNF mRNAs encoding all possible isoforms was characterised in the two neuroblastoma cell lines. We then investigated whether selective silencing of the different BDNF mRNAs using specific siRNAs could reduce cell survival in response to serum deprivation or the anticancer drugs cisplatin, doxorubicin and etoposide. We found that three isoforms located in the second exon cluster are essential for neuroblastoma cell survival under cytotoxic stress. Notably, promoters of the second exon cluster, but not the first, are controlled by Ca2+-sensitive elements.

Cdk1-FOXO1: a mitotic signal takes center stage in post-mitotic neurons

An emerging theme in molecular neurobiology is the discovery of post-mitotic functions for proteins classically associated with mitotic transition in cycling cells. Although neurons have departed the cell cycle, they surprisingly express molecules in the cell cycle apparatus throughout development. The major mitotic cyclin-dependent kinase Cdk1 plays a critical role during the period of naturally occurring neuronal death in the nervous system and has been suggested to contribute to the pathogenesis of neurodegenerative diseases. However, the mechanisms by which Cdk1 promotes neuronal apoptosis are incompletely understood. A recent report by Yuan et al., (2008) has identified a direct relationship between this mitotic kinase and forkhead transcription factor FOXO1, a protein previously implicated in cell death, DNA damage repair and tumor suppression. Here we will discuss the key findings of this report and consider the implications of this mechanism to the regulation of other signal transduction pathways in brain development and diseases.

Glaucoma alters the expression of NGF and NGF receptors in visual cortex and geniculate nucleus of rats: effect of eye NGF application

We investigated the effect of glaucoma (GL) on nerve growth factor (NGF) presence in two brain visual areas. Rats with elevated intraocular pressure (EIOP), induced by hypertonic saline injection in the episcleral vein, were treated with eye topical application of saline or NGF. Rats were subsequently sacrificed, and brain tissues were used for immunohistochemical, biochemical, and molecular analyses. We found that GL alters the basal level of NGF and NGF receptors in brain visual centers and that NGF eye application normalized these deficits. These findings demonstrate that the reduced presence of NGF can arise due to degenerative events in retinal and brain visual areas.

Reduced NGF level and TrkA protein and TrkA gene expression in the optic nerve of rats with experimentally induced glaucoma

Glaucoma (GL) is an optic neuropathy characterized by progressive loss of visual field due to retinal cell death and optic nerve (ON) degeneration, usually in response to abnormal elevated intraocular pressure (EIOP). It has previously demonstrated that cells of the ON express nerve growth factor (NGF) and NGF-receptors. Relatively little is known, however, about their role on the ON of the glaucomatous eye. The aim of the study was to elucidate this aspect. Using a rat model of GL we investigated the response of NGF and NGF-receptors in the ON of subjects with experimentally induced EIOP. Our results show that EIOP significantly impairs the presence of NGF and NGF-receptor proteins and TrkA gene expression in the ON of glaucomatous eye. These findings suggest that NGF and NGF-receptor might be important signals for the ON response in the EIOP.

Retinal p75 and bax overexpression is associated with retinal ganglion cells apoptosis in a rat model of glaucoma

PURPOSE

The administration of neurotrophins has been clearly demonstrated to support survival of retina cells during a variety of insults. Increased levels of neurotrophins, such as the nerve growth factor (NGF), have been found in experimental models of glaucoma. Nevertheless, loss of retinal cells does occur in the course of ocular hypertension. Therefore, this study sought to address whether timely changes in NGF and its receptors, trkA(NGFR) and p75(NTR), might explain the progression of retinal damage during experimental glaucoma.

METHODS

A well-characterized technique to induce glaucoma in rats was utilized. The animals were sacrificed after 10, 20 and 35 days from induction of glaucoma. Retinal ganglion cell (RGC) apoptosis, retinal expression of NGF protein as well as Bcl-2, Bax, trkA(NGFR) and p75(NTR) transcript expression were detected. The balance between trkA(NGFR) and p75(NTR) was examined, considering their anti- and pro-apoptotic role in cell death, respectively.

RESULTS

We demonstrated that in our model of experimental glaucoma, the loss of retinal ganglion cells (RGCs) is accompanied by a timely increase of retinal NGF. Moreover, we found that the trkA(NGFR)/p75(NTR) mRNA ratio and the Bcl-2/Bax mRNA were both decreased, indicating a p75(NGFR) and Bax over-expression.

CONCLUSIONS

Retinal NGF is over-expressed in experimental glaucoma, but this NGF increase is not sufficient to support survival of RGCs. The failure of NGF trophic support might be associated with the progressive up-regulation of p75(NTR) in relation to trkA(NGFR).

Transglutaminase 2 and NF-kappaB interplay during NGF-induced differentiation of neuroblastoma cells

NGF treatment of neuroblastoma cells stimulates outgrowth of neurite processes associated with the expression of TrkA receptor and several differentiation markers. In this study, a 6 DIV exposure to NGF (50 ng/ml) increased immunostaining for alpha-tubulin, and expression of both alpha-tubulin and protein kinase C in the neuroblastoma cell line Neuro2a. Further, up-regulation of transglutaminase 1 and transglutaminase 2 expression, and reduction of transglutaminase 3 levels, were also observed in NGF-treated cells in comparison to untreated cells. Moreover, when Neuro2a cells were treated with the specific NF-kappaB inhibitor SN-50, the strong reduction of NF-kappaB activation was concomitant with a significant decrease of transglutaminase 2 expression, suggesting that NGF-evoked transglutaminase 2 induction could be related to NF-kappaB activation. To characterize the possible transglutaminase 2/NF-kappaB interplay, NGF treatment was carried out in Neuro2a cells which already over-expressed transglutaminase 2 after retinoic acid treatment. An additive effect of NGF was observed on the retinoic acid-induced transglutaminase 2 expression and enzyme activity, and NF-kappaB activation. However, a cystamine-mediated significant inhibition of transglutaminase activity (70%) was accompanied by a drastically reduced NF-kappaB activation only in cells exposed to NGF following retinoic acid treatment. We hypothesize that NF-kappaB activation was dependent on the transamidating activity related to high levels of TG2, and NGF enhanced NF-kappaB activation by a different, synergistically acting, pathway. These data suggest that the combined use of NGF and retinoic acid, or mimicking drugs, may provide the basics for the development of novel strategies in the therapeutic management of neuroblastomas.

Neurotrophin receptor expression in human primary retinoblastomas and retinoblastoma cell lines

BACKGROUND

Neurotrophin receptor signaling regulates proliferation, differentiation and death of neuronal cells. Expression of Trk receptors has been implicated in the pathogenesis and prognosis of embryonal tumors, including neuroblastoma, nephroblastoma, and medulloblastoma.

PROCEDURE

We analyzed TrkA, TrkB, TrkC, and p75 expression using semi-quantitative RT-PCR in 23 retinoblastomas and 8 retinoblastoma cell lines. Comparison of mRNA expression with clinical variables as well as the proliferation (PI) and apoptotic index (AI) of the tumor, was performed by Pearson correlation analysis and two-sample t-test.

RESULTS

Almost all tumor samples and cell lines demonstrated high expression of all Trk receptors. Expression of TrkB and its ligand, BDNF, was most pronounced, suggesting TrkB to be the major Trk receptor involved in retinoblastoma biology. In contrast, p75 expression was substantially reduced in a subset of tumors and cell lines, in particular compared to its expression in normal retina. Tumors with infiltrative growth demonstrated significantly lower relative levels of TrkC expression than localized tumors (P = 0.004). High expression of TrkA was associated with a higher AI (P = 0.04), and high expression of TrkC was associated with a younger age of the patients (P = 0.03). Inhibition of Trk signaling by K252a resulted in marked growth inhibition of retinoblastoma cells in vitro.

CONCLUSIONS

Our findings suggest a role for neurotrophin signaling in the biology of retinoblastoma. General Trk inhibitors are effective in decreasing growth rates of retinoblastoma cells in vitro, and should be evaluated in in vivo studies.

Differential effects of Th1, monocyte/macrophage and Th2 cytokine mixtures on early gene expression for glial and neural-related molecules in central nervous system mixed glial cell cultures: neurotrophins, growth factors and structural proteins

Background

In multiple sclerosis, inflammatory cells are found in both active and chronic lesions, and it is increasingly clear that cytokines are involved directly and indirectly in both formation and inhibition of lesions. We propose that cytokine mixtures typical of Th1 or Th2 lymphocytes, or monocyte/macrophages each induce unique molecular changes in glial cells.

Methods

To examine changes in gene expression that might occur in glial cells exposed to the secreted products of immune cells, we have used gene array analysis to assess the early effects of different cytokine mixtures on mixed CNS glia in culture. We compared the effects of cytokines typical of Th1 and Th2 lymphocytes and monocyte/macrophages (M/M) on CNS glia after 6 hours of treatment.

Results

In this paper we focus on changes with potential relevance for neuroprotection and axon/glial interactions. Each mixture of cytokines induced a unique pattern of changes in genes for neurotrophins, growth and maturation factors and related receptors; most notably an alternatively spliced form of trkC was markedly downregulated by Th1 and M/M cytokines, while Th2 cytokines upregulated BDNF. Genes for molecules of potential importance in axon/glial interactions, including cell adhesion molecules, connexins, and some molecules traditionally associated with neurons showed significant changes, while no genes for myelin-associated genes were regulated at this early time point. Unexpectedly, changes occurred in several genes for proteins initially associated with retina, cancer or bone development, and not previously reported in glial cells.

Conclusion

Each of the three cytokine mixtures induced specific changes in gene expression that could be altered by pharmacologic strategies to promote protection of the central nervous system.

Myelin basic protein-primed T cells induce neurotrophins in glial cells via alphavbeta3 [corrected] integrin

Increasing the level of neurotrophins within the central nervous system may have therapeutic efficacy in patients with various neurological diseases. Earlier we have demonstrated that myelin basic protein (MBP)-primed T cells induce the expression of various proinflammatory molecules in glial cells via cell-to-cell contact. Here we describe that after Th2 polarization by gemfibrozil or other drugs, MBP-primed T cells induced the expression of neurotrophic molecules such as brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3), but not proinflammatory molecules in microglia and astroglia via cell-to-cell contact. MBP-primed Th2 cells expressed alpha5 and beta3 integrins and functional blocking antibodies against both alpha5 and beta3 integrins inhibited the ability of MBP-primed Th2 cells to induce glial neurotrophins. On the other hand, glial cells expressed PDGF-Rbeta and neutralization of this glial receptor abrogated the ability of Th2 cells to induce neurotrophins in glia. Activation of glial cAMP response element-binding protein (CREB) by MBP-primed Th2 cell contact and inhibition of contact-mediated expression of neurotrophins by antisense knockdown of glial CREB suggest that MBP-primed Th2 cell-glia contact induces the expression of neurotrophins through glial activation of CREB. Accordingly, blocking of either alpha5beta3 integrins on T cells or PDGF-Rbeta on glial cells impaired the ability of MBP-primed Th2 cells to induce glial activation of CREB. Furthermore, we demonstrate that these MBP-primed Th2 cells entered into the central nervous system and increased the expression of neurotrophins in vivo in the brain. This study illuminates the importance of alpha5beta3 and PDGF-Rbeta in guiding the novel neurotrophic property of neuroantigen-primed T cells via activation of CREB that may be of therapeutic importance in various neurological disorders.

Clathrin-mediated endocytic signals are required for the regeneration of,as well as homeostasis in, the planarian CNS

Planarians have a well-organized central nervous system (CNS), including a brain, and can regenerate the CNS from almost any portion of the body using pluripotent stem cells. In this study, to identify genes required for CNS regeneration, genes expressed in the regenerating CNS were systematically cloned and subjected to functional analysis. RNA interference (RNAi) of the planarian clathrin heavy chain (DjCHC) gene prevented CNS regeneration in the intermediate stage of regeneration prior to neural circuit formation. To analyze DjCHC gene function at the cellular level, we developed a functional analysis method using primary cultures of planarian neurons purified by fluorescence-activated cell sorting (FACS) after RNAi treatment. Using this method, we showed that the DjCHC gene was not essential for neural differentiation, but was required for neurite extension and maintenance, and that DjCHC-RNAi-treated neurons entered a TUNEL-positive apoptotic state. DjCHC-RNAi-treated uncut planarians showed brain atrophy, and the DjCHC-RNAi planarian phenotype was mimicked by RNAi-treated planarians of the mu-2 (μ2)gene, which is involved in endocytosis, but not the mu-1(μ1) gene, which is involved in exocytosis. Thus,clathrin-mediated endocytic signals may be required for not only maintenance of neurons after synaptic formation, but also axonal extension at the early stage of neural differentiation.

Selective role for RGS12 as a Ras/Raf/MEK scaffold in nerve growth factor-mediated differentiation

Regulator of G-protein signaling (RGS) proteins accelerate GTP hydrolysis by heterotrimeric G-protein alpha subunits and thus inhibit signaling by many G protein-coupled receptors. Several RGS proteins have a multidomain architecture that adds further complexity to their roles in cell signaling in addition to their GTPase-accelerating activity. RGS12 contains a tandem repeat of Ras-binding domains but, to date, the role of this protein in Ras-mediated signal transduction has not been reported. Here, we show that RGS12 associates with the nerve growth factor (NGF) receptor tyrosine kinase TrkA, activated H-Ras, B-Raf, and MEK2 and facilitates their coordinated signaling to prolonged ERK activation. RGS12 is required for NGF-mediated neurite outgrowth of PC12 cells, but not outgrowth stimulated by basic fibroblast growth factor. siRNA-mediated knockdown of RGS12 expression also inhibits NGF-induced axonal growth in dissociated cultures of primary dorsal root ganglia neurons. These data suggest that RGS12 may play a critical, and receptor-selective, role in coordinating Ras-dependent signals that are required for promoting and/or maintaining neuronal differentiation.

What is the biological significance of BDNF mRNA targeting in the dendrites? Clues from epilepsy and cortical development

The neurotrophin brain-derived neurotrophic factor (BDNF) is a regulatory factor of several, partially contrasting, aspects of the biology of neural cells, including survival, growth, differentiation, and cell death. Regulation of the local availability of BDNF at distinct subcellular domains such as the cell soma, dendrites, axons, and spines appears to be the key to conferring spatial and temporal specificity of the different effects elicited by this neurotrophin. This article reviews recent findings in the context of epileptogenesis and visual cortex maturation that showed that different BDNF messenger RNA (mRNA) transcripts are localized at different subcellular locations in hippocampal and cortical neurons. It also reviews findings demonstrating that strong depolarizing stimuli, both in vitro and in vivo, elicit accumulation of BDNF mRNA and protein in the distal dendrites through a signaling pathway involving the activation of the N-methyl-D-aspartate and tyrosine kinase B receptors and an intracellular increase in Ca2+ concentration. Finally, this article proposes that the regulation of the delivery of BDNF mRNA and protein to the different subcellular domains--particularly the dendritic compartment--may represent a fundamental aspect of the processes of cellular and synaptic morphological rearrangements underlying epileptogenesis and postnatal development of the visual cortex.

Clear cell sarcoma of the kidney: up-regulation of neural markers with activation of the sonic hedgehog and Akt pathways

PURPOSE AND EXPERIMENTAL DESIGN

Clear cell sarcoma of the kidney (CCSK), the second most common renal tumor in children, poses significant diagnostic challenges. No positive diagnostic markers are available, and the pathogenesis of CCSK remains an enigma. To address these challenges, the gene expression patterns of 14 CCSKs were compared with 15 Wilms tumors and 3 fetal kidney samples using oligonucleotide arrays.

RESULTS

Using unsupervised methods, the gene expression profile of CCSK was distinctive: differentially expressed genes could largely be grouped into four categories: (a) a wide variety of neural markers, (b) members of the Sonic hedgehog pathway, (c) members of the phosphoinositide-3-kinase/Akt cell proliferation pathway, and (d) known therapeutic targets. Corresponding changes in critical proteins using Western blot and/or immunohistochemistry confirmed the up-regulation of these pathways and proteins. In particular, CD117 and epidermal growth factor receptor are up-regulated at the protein level in many CCSKs, providing potential therapeutic targets. One of the neural markers, nerve growth factor receptor, represents a promising diagnostic tool for CCSK.

CONCLUSIONS

This study suggests that CCSKs arise within a renal mesenchymal cell that shows a wide variety of neural markers. As such, it seems to be susceptible to genetic changes also seen in a variety of other neuroectodermal and neuronal tumors, including activation of Sonic hedgehog and phosphoinositide-3-kinase/Akt pathways. Involvement of these pathways in CCSKs implicates their widening role in tumorigenesis.

Novel role of sphingosine kinase 1 as a mediator of neurotrophin-3 action in oligodendrocyte progenitors

We had found previously that neurotrophin-3 (NT-3) is a potent stimulator of cAMP-response element binding protein (CREB) phosphorylation in cultured oligodendrocyte progenitors. Here, we show that CREB phosphorylation in these cells is also highly stimulated by sphingosine-1-phosphate (S1P), a sphingolipid metabolite that is known to be a potent mediator of numerous biological processes. Moreover, CREB phosphorylation in response to NT-3 involves sphingosine kinase 1 (SphK1), the enzyme that synthesizes S1P. Immunocytochemistry and confocal microscopy indicated that NT-3 induces translocation of SphK1 from the cytoplasm to the plasma membrane of oligodendrocytes, a process accompanied by increased SphK1 activity in the membrane fraction where its substrate sphingosine resides. To examine the involvement of SphK1 in NT-3 function, SphK1 expression was down-regulated by treatment with SphK1 sequence-specific small interfering RNA. Remarkably, the capacity of NT-3 to protect oligodendrocyte progenitors from apoptotic cell death induced by growth factor deprivation was abolished by down-regulating the expression of SphK1, as assessed by terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL) assay. Altogether, these results suggest that SphK1 plays a crucial role in the stimulation of oligodendrocyte progenitor survival by NT-3, and demonstrate a functional link between NT-3 and S1P signaling, adding to the complexity of mechanisms that modulate neurotrophin function and oligodendrocyte development.

Retinal ganglion cell death is delayed by activation of retinal intrinsic cell survival program

Neuronal cells undergo apoptosis when deprived of neurotrophic factors due to injury, trauma, or neurodegenerative disease. This study examined cell death in the retina after chronic elevation of intraocular pressure (IOP) in an experimental rat model of human glaucomatous disease. Three episcleral veins on the ocular surface of rats were cauterized. Activation of several cell death programs represented by Fas ligand, FADD (Fas Associated Death Domain/Mort1) and the caspase cascade (caspase-8 and -3) and survival programs represented by phosphorylated protein kinase B (PKB/Akt), Bcl-2 associated death domain (BAD), and cAMP responsive element binding protein (CREB) were examined using immunohistochemistry and Western blotting. Following injury, two major events occurred simultaneously in the retina: activation of programmed cell death pathways and activation of survival mechanisms to maintain the cellular homeostasis of the retina. At the later stage of injury, markers of an activated cell death program appeared to be concentrated in the retinal ganglion cells. In conclusion, we suggest that endogenous cell survival factors triggered at the early stage of injury play a critical role in control of the death or survival of retinal ganglion cells and that the manipulation of this decision phase is one of the therapeutic targets for glaucoma.