Neurotrophin Receptor TrkB Research Articles

BNN-20, a synthetic microneurotrophin, strongly protects dopaminergic neurons in the “weaver” mouse, a genetic model of dopamine-denervation, acting through the TrkB neurotrophin receptor

Neurotrophic factors are among the most promising treatments aiming at slowing or stopping and even reversing Parkinson's disease (PD). However, in most cases, they cannot readily cross the human blood-brain-barrier (BBB).Herein, we propose as a therapeutic for PD the small molecule 17-beta-spiro-[5-androsten-17,2'-oxiran]-3beta-ol (BNN-20), a synthetic analogue of DHEA, which crosses the BBB and is deprived of endocrine side-effects. Using the “weaver” mouse, a genetic model of PD, which exhibits progressive dopaminergic neurodegeneration in the Substantia Nigra (SN), we have shown that long-term administration (P1-P21) of BNN-20 almost fully protected the dopaminergic neurons and their terminals, via i) a strong anti-apoptotic effect, probably mediated through the Tropomyosin receptor kinase B (TrkB) neurotrophin receptor's PI3K-Akt-NF-κB signaling pathway, ii) by exerting an efficient antioxidant effect, iii) by inducing significant anti-inflammatory activity and iv) by restoring Brain-Derived Neurotrophic Factor (BDNF) levels. By intercrossing “weaver” with NGL mice (dual GFP/luciferase-NF-κΒ reporter mice, NF-κΒ.GFP.Luc), we obtained Weaver/NGL mice that express the NF-κB reporter in all somatic cells. Acute BNN-20 administration to Weaver/NGL mice induced a strong NF-κB-dependent transcriptional response in the brain as detected by bioluminescence imaging, which was abolished by co-administration of the TrkB inhibitor ANA-12. This indicates that BNN-20 exerts its beneficial action (at least in part) through the TrkB-PI3K-Akt-NF-κB signaling pathway.These results could be of clinical relevance, as they suggest BNN-20 as an important neuroprotective agent acting through the TrkB neurotrophin receptor pathway, mimicking the action of the endogenous neurotrophin BDNF. Thus BNN-20 could be proposed for treatment of PD.

Cooperation of neurotrophin receptor TrkB and Her2 in breast cancer cells facilitates brain metastases

BackgroundPatients with primary breast cancer that is positive for human epidermal growth factor receptor 2 (Her2+) have a high risk of developing metastases in the brain. Despite gains with systemic control of Her2+ disease using molecular therapies, brain metastases remain recalcitrant to therapeutic discovery. The clinical predilection of Her2+ breast cancer cells to colonize the brain likely relies on paracrine mechanisms. The neural niche poses unique selection pressures, and neoplastic cells that utilize the brain microenvironment may have a survival advantage.MethodsTropomyosin-related kinase B (TrkB), Her2, and downstream targets were analyzed in primary breast cancer, breast-to-brain metastasis (BBM) tissues, and tumor-derived cell lines using quantitative real-time PCR, western blot, and immunohistochemical assessment. TrkB function on BBM was confirmed with intracranial, intracardiac, or mammary fat pad xenografts in non-obese diabetic/severe combined immunodeficiency mice. The function of brain-derived neurotrophic factor (BDNF) on cell proliferation and TrkB/Her2 signaling and interactions were confirmed using selective shRNA knockdown and selective inhibitors. The physical interaction of Her2-TrkB was analyzed using electron microscopy, co-immunoprecipitation, and in silico analysis. Dual targeting of Her2 and TrkB was analyzed using clinically utilized treatments.ResultsWe observed that patient tissues and cell lines derived from Her2+ human BBM displayed increased activation of TrkB, a neurotrophin receptor. BDNF, an extracellular neurotrophin, with roles in neuronal maturation and homeostasis, specifically binds to TrkB. TrkB knockdown in breast cancer cells led to decreased frequency and growth of brain metastasis in animal models, suggesting that circulating breast cancer cells entering the brain may take advantage of paracrine BDNF-TrkB signaling for colonization. In addition, we investigated a possible interaction between TrkB and Her2 receptors on brain metastatic breast cancer cells, and found that BDNF phosphorylated both its cognate TrkB receptor and the Her2 receptor in brain metastatic breast cancer cells.ConclusionCollectively, our findings suggest that heterodimerization of Her2 and TrkB receptors gives breast cancer cells a survival advantage in the brain and that dual inhibition of these receptors may hold therapeutic potential.

Neurite outgrowth in cultured mouse pelvic ganglia - Effects of neurotrophins and bladder tissue.

Neurotrophic factors regulate survival and growth of neurons. The urinary bladder is innervated via both sympathetic and parasympathetic neurons located in the major pelvic ganglion. The aim of the present study was to characterize the effects of the neurotrophins nerve growth factor (NGF), brain derived neurotrophic factor (BDNF) and neurotrophin 3 (NT-3) on the sprouting rate of sympathetic and parasympathetic neurites from the female mouse ganglion. The pelvic ganglion was dissected out and attached to a petri dish and cultured in vitro. All three factors (BDNF, NT-3 and NGF) stimulated neurite outgrowth of both sympathetic and parasympathetic neurites although BDNF and NT-3 had a higher stimulatory effect on parasympathetic ganglion cells. The neurotrophin receptors TrkA, TrkB and TrkC were all expressed in neurons of the ganglia. Co-culture of ganglia with urinary bladder tissue, but not diaphragm tissue, increased the sprouting rate of neurites. Active forms of BDNF and NT-3 were detected in urinary bladder tissue using western blotting whereas tissue from the diaphragm expressed NGF. Neurite outgrowth from the pelvic ganglion was inhibited by a TrkB receptor antagonist. We therefore suggest that the urinary bladder releases trophic factors, including BDNF and NT-3, which regulate neurite outgrowth via activation of neuronal Trk-receptors. These findings could influence future strategies for developing pharmaceuticals to improve re-innervation due to bladder pathologies.

A Review on Ubiquitination of Neurotrophin Receptors: Facts and Perspectives.

Ubiquitination is a reversible post-translational modification involved in a plethora of different physiological functions. Among the substrates that are ubiquitinated, neurotrophin receptors (TrkA, TrkB, TrkC, and p75NTR) have been studied recently. TrkA is the most studied receptor in terms of its ubiquitination, and different E3 ubiquitin ligases and deubiquitinases have been implicated in its ubiquitination, whereas not much is known about the other neurotrophin receptors aside from their ubiquitination. Additional studies are needed that focus on the ubiquitination of TrkB, TrkC, and p75NTR in order to further understand the role of ubiquitination in their physiological and pathological functions. Here we review what is currently known regarding the ubiquitination of neurotrophin receptors and its physiological and pathological relevance.

Nanoscale clustering of the neurotrophin receptor TrkB revealed by super-resolution STED microscopy.

The nanoscale organization of the tropomyosin-related kinase receptor type B (TrkB), a promising therapeutic target for severe neurodegenerative and psychiatric disorders, is examined by stimulated emission depletion (STED) microscopy using the deconvoluted gated STED option. The performed immunofluorescence nanoscopic subdiffraction imaging of the membrane receptor localization reveals that clusters of oligomeric TrkB states and randomly organized nanodomains are formed in the membranes of differentiated human neuroblastoma SH-SY5Y cells, which are studied as an in vitro model of neurodegeneration. Despite that the monomeric (isolated) states of the receptor cannot be distinguished from its dimeric forms in such images, TrkB receptor dimers (or couple of individual monomers) are visualized at super-resolution as single pixels in the magnified Huygens-deconvoluted gated STED images. The clusters of higher-order TrkB oligomers are of dynamic nature rather than of a fixed stoichiometry. The propensity for membrane protein clustering as well as the dissociation of the TrkB receptors nanodomains can be modulated by neurotherapeutic formulations containing ω-3 polyunsaturated docosahexaenoic acid (DHA). Nanomolar concentrations of DHA change the receptor topology and lead to disruption of the cluster phases. This result is of therapeutic importance for TrkB receptor availability upon ligand binding as DHA favours the mobility and the dynamic distribution of the protein populations in the cell membranes.

Flux of signalling endosomes undergoing axonal retrograde transport is encoded by presynaptic activity and TrkB.

Axonal retrograde transport of signalling endosomes from the nerve terminal to the soma underpins survival. As each signalling endosome carries a quantal amount of activated receptors, we hypothesized that it is the frequency of endosomes reaching the soma that determines the scale of the trophic signal. Here we show that upregulating synaptic activity markedly increased the flux of plasma membrane-derived retrograde endosomes (labelled using cholera toxin subunit-B: CTB) in hippocampal neurons cultured in microfluidic devices, and live Drosophila larval motor neurons. Electron and super-resolution microscopy analyses revealed that the fast-moving sub-diffraction-limited CTB carriers contained the TrkB neurotrophin receptor, transiently activated by synaptic activity in a BDNF-independent manner. Pharmacological and genetic inhibition of TrkB activation selectively prevented the coupling between synaptic activity and the retrograde flux of signalling endosomes. TrkB activity therefore controls the encoding of synaptic activity experienced by nerve terminals, digitalized as the flux of retrogradely transported signalling endosomes.

Localization of TrkB and p75 receptors in peritoneal and deep infiltrating endometriosis: an immunohistochemical study.

BackgroundThe roles of the neurotrophins NGF (Neurotrophic growth factor) and BDNF (brain-derived neurotrophic factor) in neuronal growth and development are already known. Meanwhile, the neurotrophin receptors TrkA (tropomyosin related kinase A), TrkB, and p75 are important for determining the fate of cells. In endometriosis, this complex system has not been fully elucidated yet. The aim of this study was to evaluate the expression and location of these neurotrophins and their receptors in peritoneal (PE) and deep infiltrating endometriotic (DIE) tissues and to measure and compare the density of nerve fibers in the disease subtypes.MethodsPE lesions (n = 20) and DIE lesions (n = 22) were immunostained and analyzed on serial slides with anti-BDNF, −NGF, −TrkA, −TrkB, −p75,-protein gene product 9.5 (PGP9.5, intact nerve fibers) and -tyrosine hydroxylase (TH, sympathetic nerve fibers) antibodies.ResultThere was an equally high percentage (greater than 75 %) of BDNF-positive immunostaining cells in both PE and DIE. TrkB (major BDNF receptor) and p75 showed a higher percentage of immunostaining cells in DIE compared to in PE in stroma only (p < 0.014, p < 0.027, respectively). Both gland and stroma of DIE lesions had a lower percentage of NGF-positive immunostaining cells compared to those in PE lesions (p < 0.01 and p < 0.01, respectively), but there was no significant reduction in immunostaining of TrkA in DIE lesions. There was no difference in the mean density of nerve fibers stained with PGP9.5 between PE (26.27 ± 17.32) and DIE (28.19 ± 33.15, p = 0.8). When we performed sub-group analysis, the density of nerves was significantly higher in the bowel DIE (mean 57.33 ± 43.9) than in PE (mean 26.27 ± 17.32, p < 0.01) and non-bowel DIE (mean 14.6. ± 8.6 p < 0.002).ConclusionsWhile the neurotrophin BDNF is equally present in PE and DIE, its receptors TrkB and p75 are more highly expressed in DIE and may have a potential role in the pathophysiology of DIE, especially in promotion of cell growth. BDNF has a stronger binding affinity than NGF to the p75 receptor, likely inducing sympathetic nerve axonal pruning in DIE, resulting in the lower nerve fiber density seen.Electronic supplementary materialThe online version of this article (doi:10.1186/s12958-016-0178-5) contains supplementary material, which is available to authorized users.

Calpain-dependent truncated form of TrkB-FL increases in neurodegenerative processes.

Recent findings indicate that the mechanisms that drive reshaping of the nervous system are aberrantly activated in epilepsy and several neurodegenerative diseases. The recurrent seizures in epilepsy, particularly in the condition called status epilepticus, can cause permanent neurological damage, resulting in cognitive dysfunction and other serious neurological conditions. In this study, we used an in vitro model of status epilepticus to examine the role of calpain in the degeneration of hippocampal neurons. We grew neurons on a culture system that allowed studying the dendritic and axonal domains separately from the cell bodies. We found that a recently characterized calpain substrate, the neurotrophin receptor TrkB, is cleaved in the dendritic and axonal domain of neurons committed to die, and this constitutes an early step in the neuronal degeneration process. While the full-length TrkB (TrkB-FL) levels decreased, the truncated form of TrkB (Tc TrkB-FL) concurrently increased, leading to a TrkB-FL/Tc TrkB-FL imbalance, which is thought to be causally linked to neurodegeneration. We further show that the treatment with N-acetyl-Leu-Leu-norleucinal, a specific calpain activity blocker, fully protects the neuronal processes from degeneration, prevents the TrkB-FL/Tc TrkB-FL imbalance, and provides full neuroprotection. Moreover, the use of the TrkB antagonist ANA 12 at the time when the levels of TrkB-FL were significantly decreased, totally blocked neuronal death, suggesting that Tc TrkB-FL may have a role in neuronal death. These results indicate that the imbalance of these neurotrophins receptors plays a key role in neurite degeneration induced by seizures.

A Phytochrome Sensory Domain Permits Receptor Activation by Red Light.

Optogenetics and photopharmacology enable the spatio-temporal control of cell and animal behavior by light. Although red light offers deep-tissue penetration and minimal phototoxicity, very few red-light-sensitive optogenetic methods are currently available. We have now developed a red-light-induced homodimerization domain. We first showed that an optimized sensory domain of the cyanobacterial phytochrome 1 can be expressed robustly and without cytotoxicity in human cells. We then applied this domain to induce the dimerization of two receptor tyrosine kinases-the fibroblast growth factor receptor 1 and the neurotrophin receptor trkB. This new optogenetic method was then used to activate the MAPK/ERK pathway non-invasively in mammalian tissue and in multicolor cell-signaling experiments. The light-controlled dimerizer and red-light-activated receptor tyrosine kinases will prove useful to regulate a variety of cellular processes with light.

Selective Requirement for Maintenance of Synaptic Contacts onto Motoneurons by Target-Derived trkB Receptors.

Synaptic contacts onto motoneurons were studied in mice in which the gene for the trkB neurotrophin receptor was knocked out selectively in a subset of spinal motoneurons. The extent of contacts by structures immunoreactive for either of two different vesicular glutamate transporters (VGLUT1 and VGLUT2), the vesicular GABA transporter, or glutamic acid decarboxylase 67 (GAD67) with the somata of motoneurons, was studied in wild type and trkB knockout cells in tamoxifen treated male and female SLICK-trkB−/− mice. Selective knockout of the trkB gene resulted in a marked reduction in contacts made by VGLUT2- and GAD67-immunoreactive structures in both sexes and a significant reduction in contacts containing only glycine in male mice. No reduction was found for glycinergic contacts in female mice or for VGLUT1 immunoreactive contacts in either sex. Signaling through postsynaptic trkB receptors is considered to be an essential part of a cellular mechanism for maintaining the contacts of some, but not all, synaptic contacts onto motoneurons.

TrkB Promotes Breast Cancer Metastasis via Suppression of Runx3 and Keap1 Expression.

In metastatic breast cancer, the acquisition of malignant traits has been associated with the increased rate of cell growth and division, mobility, resistance to chemotherapy, and invasiveness. While screening for the key regulators of cancer metastasis, we observed that neurotrophin receptor TrkB is frequently overexpressed in breast cancer patients and breast cancer cell lines. Additionally, we demonstrate that TrkB expression and clinical breast tumor pathological phenotypes show significant correlation. Moreover, TrkB expression was significantly upregulated in basal-like, claudin-low, and metaplastic breast cancers from a published microarray database and in patients with triple-negative breast cancer, which is associated with a higher risk of invasive recurrence. Interestingly, we identified a new TrkB-regulated functional network that is important for the tumorigenicity and metastasis of breast cancer. We demonstrated that TrkB plays a key role in regulation of the tumor suppressors Runx3 and Keap1. A markedly increased expression of Runx3 and Keap1 was observed upon knockdown of TrkB, treatment with a TrkB inhibitor, and in TrkB kinase dead mutants. Additionally, the inhibition of PI3K/AKT activation significantly induced Runx3 and Keap1 expression. Furthermore, we showed that TrkB enhances metastatic potential and induces proliferation. These observations suggest that TrkB plays a key role in tumorigenicity and metastasis of breast cancer cells through suppression of Runx3 or Keap1 and that it is a promising target for future intervention strategies for preventing tumor metastasis and cancer chemoprevention.

Abstract C187: Cross-inhibition of Trk receptors by TAS-119, a novel Aurora A selective inhibitor, exhibits therapeutic potential in a Trk-driven cancer model

Abstract Background; Comprehensive analysis by next-generation sequencing has identified oncogenic gene rearrangement of Trk neurotrophin receptors TrkA, TrkB and TrkC (encoded by NTRK1, NTRK2, and NTRK3 gene, respectively) in multiple tumor types including lung adenocarcinoma, colorectal cancer, glioblastoma and acute myeloid leukemia. The creation of gene fusion through genomic rearrangement results in constitutive activation of the kinase domain of Trk. These recent findings encourage study of the therapeutic potential of Trk kinases as drug targets for the specific treatment of patients with oncogenic NTRK gene abnormalities. TAS-119 is a novel small molecular weight inhibitor of Aurora A kinase and currently investigated in phase 1 clinical trial as both an enhancer of microtubule stabilizing drugs and monotherapy (1-3). In addition, TAS-119 shows pan-Trk inhibition with potency similar to Aurora A inhibition. Here, we describe the in vitro and in vivo pharmacologic profile of TAS-119 as a pan-Trk inhibitor. Methods; Kinase assays were performed with purified recombinant enzymes under optimized conditions using ATP concentration at or just below the respective Km. In cell proliferation studies, cell viability was determined at 72 hour by detecting cellular ATP concentration. Analysis of protein expression including phosphorylated proteins was conducted by Western blotting. In tumor xenograft models, cells were implanted subcutaneously in nude mice. TAS-119 was administered orally with twice daily or intermittent dosing (4 days on/ 3 days off schedule) for 14 days. Results; TAS-119 inhibited TrkA activity with an IC50 of 1 nM in cell-free system, and inhibited TrkA autophosphorylation and cell proliferation of KM12C colorectal cancer cell line harbouring TPM3-TrkA fusions at sub-nM range. In the KM12C xenograft model, both continuous and intermittent treatment with TAS-119 at 60 mg/kg or 100 mg/kg b.i.d. for 14 days resulted in dose-dependent inhibition of tumor growth with good tolerability. Delays of tumor growth in xenograft model were well correlated with reduction of TrkA autophosphorylation and inhibition of downstream signal transduction like pPLCγ, pERK and pAKT within tumors. Conclusions; TAS-119 is an orally bioavailable dual-specificity kinase inhibitor developed specifically for both Trk and Aurora A inhibition with favorable profiles in animals. These preclinical data suggest that TAS-119 has therapeutic potential for cancers with Trk rearrangements. Currently, phase 1 dose-escalation clinical trial is ongoing. Although TAS-119 is primarily being developed as an inhibitor for Aurora A kinase, it should also be tested clinically in patients with tumors showing Trk gene rearrangement. 1) 24th EORTC-NCI-AACR Symposium (2012), abstract #251 and #252 2) 25th EORTC-NCI-AACR Symposium (2013), abstract #A268 and #A269 3) 26th EORTC-NCI-AACR Symposium (2014), abstract #P005 and #P178 Citation Format: Hiroshi Sootome, Akihiro Miura, Kimihiro Ito, Takamasa Suzuki, Hiroshi Hirai, Teruhiro Utsugi, Kazuhiko Yonekura. Cross-inhibition of Trk receptors by TAS-119, a novel Aurora A selective inhibitor, exhibits therapeutic potential in a Trk-driven cancer model. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr C187.

A novel natural product inspired scaffold with robust neurotrophic, neurogenic and neuroprotective action.

In search for drugs to treat neuropsychiatric disorders wherein neurotrophic and neurogenic properties are affected, two neurotrophically active small molecules specially crafted following natural product leads based on 2-oxa-spiro[5.5]-undecane scaffold, have been thoroughly evaluated for their neurotrophic, neurogenic and neuroprotective potential in ex vivo primary culture and in vivo zebrafish and mouse models. The outcome of in vivo investigations suggest that one of these molecules is more neurotrophic than neurogenic while the other one is more neurogenic than neurotrophic and the former exhibits remarkable neuroprotection in a mouse acute ischemic stroke model. The molecular mechanisms of action of these compounds appear to be through the TrkB-MEK-ERK-CREB-BDNF pathway as pre-treatment with neurotrophin receptor TrkB inhibitor ANA-12 and MEK inhibitor PD98059 attenuates the neurotrophic action of compounds.

Expression of NGF, BDNF and their receptors in subcutaneous adipose tissue of lactating cows

Currently, there are no reports of neurotrophins in adipose tissue of cows. The distribution of nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF) and their high-affinity tyrosine kinase receptors TrkA and TrkB, was investigated by immunohistochemical method in the subcutaneous adipose tissue of cow at mid-lactation. Results revealed the localization of NGF and BDNF along the plasma membrane and cytoplasm of adipocytes. Neurotrophin receptors TrkA and TrkB showed moderate and strong positive staining in adipocytes, respectively. The expression of NGF, BDNF, TRKB — but not of TRKA — was also confirmed at transcriptional level by RT-PCR analyses.Considering the involvement of BDNF on fat metabolism and of NGF on activation of the sympathetic response in human and rodents, these neurotrophins could be related to lipogenesis and lipolysis occurring during lactation in cows. The local production of these neurotrophins supports their potential paracrine function for the regulation of adipocyte activity and deserve further investigations.

Dopamine-sensitive signaling mediators modulate psychostimulant-induced ultrasonic vocalization behavior in rats

The mesolimbic dopamine system plays a major role in psychostimulant-induced ultrasonic vocalization (USV) behavior in rodents. Within this system, psychostimulants elevate synaptic concentrations of dopamine thereby leading to exaggerated activation of postsynaptic dopamine receptors within the D1-like and D2-like subfamilies. Dopamine receptor stimulation activate several transmembrane signaling systems and cognate intracellular mediators; downstream activation of transcription factors then conveys the information from receptor activation to appropriate modulation of cellular and physiologic functions. We previously showed that cocaine-induced USV behavior was associated with enhanced expression of the neurotrophin BDNF. Like cocaine, amphetamine also increases synaptic dopamine levels, albeit primarily through facilitating dopamine release. Therefore, in the present study we investigated whether amphetamine and cocaine similarly activate dopamine-linked signaling cascades to regulate intracellular mediators leading to induction of USV behavior. The results show that amphetamine increased the emission of 50kHz USVs and this effect was blocked by SCH23390, a D1 receptor antagonist. Similar to cocaine, amphetamine increased BDNF protein expression in discrete brain regions, while pretreatment with K252a, a trkB neurotrophin receptor inhibitor, significantly reduced amphetamine-induced USV behavior. Inhibition of cyclic-AMP/PKA signaling with H89 or inhibition of PLC signaling with U73122 significantly blocked both the acute and subchronic amphetamine-induced USV behavior. In contrast, pharmacologic inhibition of either pathway enhanced cocaine-induced USV behavior. Although cocaine and amphetamine similarly modulate neurotrophin expression and USV, the molecular mechanisms by which these psychostimulants differentially activate dopamine receptor subtypes or other monoaminergic systems may be responsible for the distinct aspects of behavioral responses.

Neurotrophin receptors TrkB and TrkC promote Brain Tumor Initiating Cells growth and are novel targets for glioma therapy. (P4.242)

Neurotrophin receptors TrkB and TrkC promote Brain Tumor Initiating Cells growth and are novel targets for glioma therapy. (P4.242)

Coincidence detection in a neural correlate of classical conditioning is initiated by bidirectional 3-phosphoinositide-dependent kinase-1 signalling and modulated by adenosine receptors.

How the neural substrates for detection of paired stimuli are distinct from unpaired stimuli is poorly understood and a fundamental question for understanding the signalling mechanisms for coincidence detection during associative learning. To address this question, we used a neural correlate of eyeblink classical conditioning in an isolated brainstem from the turtle, in which the cranial nerves are directly stimulated in place of using a tone or airpuff. A bidirectional response is activated in <5 min of training, in which phosphorylated 3-phosphoinositide-dependent kinase-1 (p-PDK1) is increased in response to paired and decreased in response to unpaired nerve stimulation and is mediated by the opposing actions of neurotrophin receptors TrkB and p75(NTR) . Surprisingly, blockade of adenosine 2A (A2A ) receptors inhibits both of these responses. Pairing also induces substantially increased surface expression of TrkB that is inhibited by Src family tyrosine kinase and A2A receptor antagonists. Finally, the acquisition of conditioning is blocked by a PDK1 inhibitor. The unique action of A2A receptors to function directly as G proteins and in receptor transactivation to control distinct TrkB and p75(NTR) signalling pathways allows for convergent activation of PDK1 and protein kinase A during paired stimulation to initiate classical conditioning.

Neurotrophin Signaling via TrkB and TrkC Receptors Promotes the Growth of Brain Tumor-initiating Cells

Neurotrophins and their receptors are frequently expressed in malignant gliomas, yet their functions are largely unknown. Previously, we have shown that p75 neurotrophin receptor is required for glioma invasion and proliferation. However, the role of Trk receptors has not been examined. In this study, we investigated the importance of TrkB and TrkC in survival of brain tumor-initiating cells (BTICs). Here, we show that human malignant glioma tissues and also tumor-initiating cells isolated from fresh human malignant gliomas express the neurotrophin receptors TrkB and TrkC, not TrkA, and they also express neurotrophins NGF, BDNF, and neurotrophin 3 (NT3). Specific activation of TrkB and TrkC receptors by ligands BDNF and NT3 enhances tumor-initiating cell viability through activation of ERK and Akt pathways. Conversely, TrkB and TrkC knockdown or pharmacologic inhibition of Trk signaling decreases neurotrophin-dependent ERK activation and BTIC growth. Further, pharmacological inhibition of both ERK and Akt pathways blocked BDNF, and NT3 stimulated BTIC survival. Importantly, attenuation of BTIC growth by EGFR inhibitors could be overcome by activation of neurotrophin signaling, and neurotrophin signaling is sufficient for long term BTIC growth as spheres in the absence of EGF and FGF. Our results highlight a novel role for neurotrophin signaling in brain tumor and suggest that Trks could be a target for combinatorial treatment of malignant glioma.

Tetrahydrohyperforin: a neuroprotective modified natural compound against Alzheimer's disease.

According to the World Health Organization (WHO), a total of 35.6 million cases of dementia were estimated in 2010, with close to 7.7 million new cases each year. In 2008, WHO declared dementia a priority condition. 90% of all dementia cases are considered to be Alzheimer's disease (AD). Therefore, great effort was made to understand the etiology of the disease and stop or slow down AD progression.

CS-14 * NEUROTROPHIN RECEPTORS TrkB AND TrkC ARE REQUIRED FOR SURVIVAL OF BRAIN TUMOR INITIATING CELLS

Neurotrophins (NGF, BDNF and NT3) and their receptors (TrkA, TrkB, TrkC and p75NTR) are frequently expressed in malignant gliomas, yet their functions are largely unknown. Previously, we have shown that p75NTR is required for glioma invasion and proliferation. However, the role of other Trk receptors has not been examined. In this study, we investigated the importance of neurotrophin receptors TrkB and TrkC in survival of brain tumor initiating cells (BTICs). We used human malignant glioma tissues and also tumor-initiating cells isolated from fresh human malignant gliomas and examined the expression of neurotrophin receptors and studied their role in survival/growth these cells in vitro, we have also examined the mechanism underlie. Here, we show that human malignant glioma tissues and tumor-initiating cells express the neurotrophin receptors TrkB and TrkC, not TrkA and they also express neurotrophins NGF, BDNF and NT3. Specific activation of TrkB and TrkC receptors by ligands BDNF and NT3 stimulates Trk phosphorylation, activates Erk and Akt and enhances tumor-initiating cell viability and growth. Conversely, TrkB and TrkC knockdown or pharmacologic inhibition using inhibitors of Trk, Erk and Akt, decreases neurotrophin-dependent Trk phosphorylation, Erk and Akt activation and BTIC survival. Importantly, attenuation of BTIC growth by EGFR inhibitors could be overcome by activation of neurotrophin signaling and further neurotrophin signaling is required for maintains long-term BTIC growth in the absence of EGF and FGF, and this effect is attenuated with Trk, Erk and Akt inhibitors. In vivo experiments are under progress. Our results highlight a novel role for neurotrophin signaling in malignant glioma and suggest that Trks could be a target for combinatorial treatment.