Nerve Growth Factor Signaling Research Articles

Upregulation of Nerve Growth Factor in Central Amygdala Increases Sensitivity to Opioid Reward

The rewarding properties of opioids are essential driving force for compulsive drug-seeking and drug-taking behaviors in the development of opioid-mediated drug addiction. Prior drug use enhances sensitivity to the rewarding effects of subsequently used drugs, increasing vulnerability to relapse. The molecular mechanisms underlying this reward sensitization are still unclear. We report here that morphine that induced reward sensitization, as demonstrated by reinstatement of the behavior of conditioned place preference (CPP) with sub-threshold priming morphine, epigenetically upregulated the output activity of Ngf encoding the nerve growth factor (NGF) by increasing histone H4 acetylation in the rat central nucleus of the amygdala (CeA). NGF locally infused into the CeA mimicked the morphine effect in inducing new functional delta-opioid receptor (DOR) that was required for the reward sensitization, and morphine-induced reward sensitization was inhibited by blocking NGF receptor signaling in the CeA. Histone deacetylase inhibitors that increased the acetylation level at the Ngf promoter and NGF expression in the CeA also induced reward sensitization in a CeA NGF signaling- and DOR-dependent manner. Furthermore, CeA-applied NGF substituted prior morphine to induce reward sensitization in naive rats and also substituted priming morphine to reinstate the CPP induced by prior morphine. Thus, epigenetic upregulation of NGF activity in the CeA may promote the behavior of opioid reward and increase the sensitivity to the rewarding effect of subsequent opioids, a potentially important mechanism in drug addiction.

Oligodendroglial Process Formation is Differentially Affected by Modulating the Intra- and Extracellular Cholesterol Content

Cholesterol is an essential component of eukaryotic plasma membranes and plays an important role in membrane organization and signaling processes. It is the major lipid component of detergent resistant caveolin-1 containing rafts which previously had been reported as a platform for nerve growth factor (NGF) signaling in oligodendrocytes (OL). Surprisingly, a knockdown of caveolin-1 attenuated the process formation of OL (Schmitz et al. J Neurosci Res 88:572–588, 2010), for which a loss of cholesterol could be responsible. In the present report, we could show that a caveolin-1 knockdown resulted in an elevation of cellular cholesterol level; it may indicate an important role of caveolin-1 in cholesterol trafficking to the plasma membrane. Treatment with exogenous PEG cholesterol, which was incorporated to the plasma membrane, supported oligodendroglial process formation, in particular when OL were stimulated by NGF. In this context we have found that OL express NPC1L1 (Niemann–Pick disease type C1-Like 1) which could modulate cholesterol uptake. In contrast, depletion of membrane-bound cholesterol diminished NGF-induced process formation concomitant with a reduced activity of p42/44 mitogen-activated protein kinases.

Nerve Growth Factor in the Hippocamposeptal System: Evidence for Activity-Dependent Anterograde Delivery and Modulation of Synaptic Activity

Neurotrophins have been implicated in regulating neuronal differentiation, promoting neuronal survival, and modulating synaptic efficacy and plasticity. The prevailing view is that, depending on the target and mode of action, most neurotrophins can be trafficked and released either anterogradely or retrogradely in an activity-dependent manner. However, the prototypic neurotrophin, nerve growth factor (NGF), is not thought to be anterogradely delivered. Here we provide the neuroanatomical substrate for an anterograde hippocamposeptal transport of NGF by demonstrating its presence in mouse hippocampal GABAergic neurons and in their hippocamposeptal axons that ramify densely and abut neurons in the medial septum/diagonal band of Broca (MS/DB). We also demonstrate an activity-dependent increase in septal NGF levels that is dependent on the pattern of intrahippocampal stimulation. In addition, we show that acute exposure to NGF, via activation of TrkA, attenuates GABA(A) receptor-mediated inhibitory synaptic currents and reduces sensitivity to exogenously applied GABA. These acute actions of NGF display cell type and functional selectivity insofar as (1) they were found in cholinergic, but not GABAergic, MS/DB neurons, and (2) glutamate-mediated excitatory synaptic activity as well as AMPA-activated current responses were unaffected. Our results advocate a novel anterograde, TrkA-mediated NGF signaling in the CNS.

Hippocampal Nerve Growth Factor Potentiated by 17β-Estradiol and Involved in Allodynia of Inflamed TMJ in Rat

The hippocampus is believed to play an important role in sex-based differences of pain perception. Whether estrogen potentiates allodynia in the inflamed temporomandibular joint (TMJ) through affecting the expressions of pain-related genes in the hippocampus remains largely unknown. Because the nerve growth factor (NGF) is an important gene related to inflammatory pain, we tested whether hippocampal NGF may be involved in TMJ inflammatory pain. Here we showed that the rat hippocampal NGF was upregulated by TMJ inflammation induced by complete Freund adjuvant. NGF upregulation was further potentiated by estradiol in a dose-dependent manner. In contrast, NGF transcription in the amygdala, prefrontal cortex, and thalamus was not affected by TMJ inflammation and estradiol. An intrahippocampal injection of NGF antibody or NGF receptor inhibitor K252a (inhibitor for tropomyosin receptor kinase A, TrkA) reduced the allodynia of inflamed TMJ in proestrous rats. Our data suggest that the hippocampal NGF is involved in estradiol-sensitized allodynia of inflammatory TMJ pain. PerspectiveWe report that complete Freund adjuvant–induced temporomandibular joint (TMJ) inflammation upregulated hippocampal nerve growth factor (NGF) expression, and estradiol replacement potentiated this upregulation. These results propose that estradiol could modulate TMJ pain through the NGF signaling pathway in the hippocampus to exacerbate TMJ pain and offer a possible mechanism of sexual dimorphism of temporomandibular disorder pain.

Cholinergic Abnormalities, Endosomal Alterations and Up-Regulation of Nerve Growth Factor Signaling in Niemann-Pick Type C Disease

BackgroundNeurotrophins and their receptors regulate several aspects of the developing and mature nervous system, including neuronal morphology and survival. Neurotrophin receptors are active in signaling endosomes, which are organelles that propagate neurotrophin signaling along neuronal processes. Defects in the Npc1 gene are associated with the accumulation of cholesterol and lipids in late endosomes and lysosomes, leading to neurodegeneration and Niemann-Pick type C (NPC) disease. The aim of this work was to assess whether the endosomal and lysosomal alterations observed in NPC disease disrupt neurotrophin signaling. As models, we used i) NPC1-deficient mice to evaluate the central cholinergic septo-hippocampal pathway and its response to nerve growth factor (NGF) after axotomy and ii) PC12 cells treated with U18666A, a pharmacological cellular model of NPC, stimulated with NGF.ResultsNPC1-deficient cholinergic cells respond to NGF after axotomy and exhibit increased levels of choline acetyl transferase (ChAT), whose gene is under the control of NGF signaling, compared to wild type cholinergic neurons. This finding was correlated with increased ChAT and phosphorylated Akt in basal forebrain homogenates. In addition, we found that cholinergic neurons from NPC1-deficient mice had disrupted neuronal morphology, suggesting early signs of neurodegeneration. Consistently, PC12 cells treated with U18666A presented a clear NPC cellular phenotype with a prominent endocytic dysfunction that includes an increased size of TrkA-containing endosomes and reduced recycling of the receptor. This result correlates with increased sensitivity to NGF, and, in particular, with up-regulation of the Akt and PLC-γ signaling pathways, increased neurite extension, increased phosphorylation of tau protein and cell death when PC12 cells are differentiated and treated with U18666A.ConclusionsOur results suggest that the NPC cellular phenotype causes neuronal dysfunction through the abnormal up-regulation of survival pathways, which causes the perturbation of signaling cascades and anomalous phosphorylation of the cytoskeleton.

Nerve Growth Factor Stimulates Cellular Proliferation of Human Epithelial Ovarian Cancer

Due to its ability to induce vascular endothelial growth factor expression and proliferation, migration, and vasculogenesis of endothelial cells, nerve growth factor (NGF) has been considered as an angiogenic factor in epithelial ovarian cancer (EOC). In this work, we evaluated the angiogenic and proliferative mRNA expression profiles of EOC and addressed the responsiveness of EOC explants to NGF stimulation. Twenty EOC samples were obtained from Obstetrics and Gynecology Department, University of Chile's Clinical Hospital. Global gene expression profiles of selected poorly differentiated serous EOC samples were obtained with DNA oligonucleotide microarrays. In addition, EOC explants were subjected to NGF stimulation and levels of p-AKT, BAX, BCL2, Ki-67, c-MYC, and FOXL2 proteins were determined by immunohistochemistry. Results showed that mRNAs coding for specific transcriptional regulators and antiapoptotic components of the NGF signaling pathway were upregulated in EOC cells. At the protein level, key members of the NGF pathway including p-AKT, BCL2/BAX, Ki-67, and c-MYC were found increased, while FOXL2 was decreased in response to NGF stimulation. These findings strongly suggest that NGF stimulates cellular proliferation of human EOC.

Protein Phosphatase Magnesium Dependent 1A (PPM1A) Plays a Role in the Differentiation and Survival Processes of Nerve Cells

The serine/threonine phosphatase type 2C (PPM1A) has a broad range of substrates, and its role in regulating stress response is well established. We have investigated the involvement of PPM1A in the survival and differentiation processes of PC6-3 cells, a subclone of the PC12 cell line. This cell line can differentiate into neuron like cells upon exposure to nerve growth factor (NGF). Overexpression of PPM1A in naive PC6-3 cells caused cell cycle arrest at the G2/M phase followed by apoptosis. Interestingly, PPM1A overexpression did not affect fully differentiated cells. Using PPM1A overexpressing cells and PPM1A knockdown cells, we show that this phosphatase affects NGF signaling in PC6-3 cells and is engaged in neurite outgrowth. In addition, the ablation of PPM1A interferes with NGF-induced growth arrest during differentiation of PC6-3 cells.

Secreted VAPB/ALS8 Major Sperm Protein Domains Modulate Mitochondrial Localization and Morphology via Growth Cone Guidance Receptors

The VAPB/ALS8 major sperm protein domain (vMSP) is implicated in amyotrophic lateral sclerosis and spinal muscular atrophy, yet its function in the nervous system is not well understood. In Caenorhabditis elegans and Drosophila, the vMSP is cleaved from its transmembrane anchor and secreted in a cell type-specific fashion. We show that vMSPs secreted by neurons act on Lar-like protein-tyrosine phosphatase and Roundabout growth cone guidance receptors expressed in striated muscle. This signaling pathway promotes Arp2/3-dependent actin remodeling and mitochondrial localization to actin-rich muscle I-bands. C. elegans VAPB mutants have mitochondrial localization, morphology, mobility, and fission/fusion defects that are suppressed by Lar-like receptor or Arp2/3 inactivation. Hence, growth cone guidance receptor pathways that remodel the actin cytoskeleton have unanticipated effects on mitochondrial dynamics. We propose that neurons secrete vMSPs to promote striated muscle energy production and metabolism, in part through the regulation of mitochondrial localization and function.

Nerve growth factor and mitogen activated protein kinases alterations in rat’s sensory neurons after experimental early type 1 Diabetes: effects of electroacupuncture

Diabetic polyneuropathy (DPN), characterized by early hyperalgesia and increased nerve growth factor (NGF) availability, evolves in late irreversible neuropathic symptoms with reduced NGF support to sensory neurons. Electroacupuncture (EA) modulates NGF presence and activity in the peripheral nervous system, being effective for the treatment of DPN symptoms Our working hypotheses are that NGF plays an important pathogenic role in DPN development while EA could be useful in the therapy of DPN by modulating NGF expression and activity. Diabetes was induced in rats by streptozotocin (STZ) injection. One week after STZ, EA treatments were started and continued for three weeks. NGF system and hyperalgesia-related mediators were analyzed in the dorsal root ganglia (DRG), and in their spinal and skin innervation territories. Four weeks diabetes inceased NGF and NGF receptors and deregulated intracellular signaling mediators of DRG neurons hyper-sensitizations. EA in diabetic rats decreased both NGF and NGF receptors, normalized c-Jun N-terminal and p38 kinases activation, decreased transient receptor potential vanilloid-1 ion channel and possibly activated Nf-κB. Increase of NGF signaling might play an important role in the development of DPN. EA represent a supportive tools aimed at controlling DPN by modulating NGF signaling in diabetestargeted neurons.

Increased expression of the homologue of enhancer-of-split 1 protects neurons from beta amyloid neurotoxicity and hints at an alternative role for transforming growth factor beta1 as a neuroprotector

IntroductionAlzheimer's disease (AD) is a neurodegenerative disorder characterized by the deposition of β-amyloid (Aβ) in the brain, which produces progressive neuronal loss and dementia. We recently demonstrated that the noxious effects of Aβ on cultured hippocampal neurons are in part provoked by the antagonism of nerve growth factor (NGF) signalling, which impairs the activation of nuclear factor κB (NF-κB) by impeding the tyrosine phosphorylation of I-κBα. As a result, the expression of the homologue of Enhancer-of split 1 (Hes1) gene is downregulated and ultimately, gamma-aminobutyric acid (GABA)-ergic connectivity is lost.MethodsHes1 activity was promoted in cultured hippocampal neurons by overexpressing a Hes1-encoding plasmid or by upregulating this gene by activating NF-κB through different approaches (overexpressing either the I-κB kinaseβ, or p65/RelA/NF-κB). Alternatively neurons were exposed to TGFβ1. Dendrite patterning, GABAergic connectivity and cell survival were analyzed by immunofluorescence microscopy. Hes1 expression was determined by real-time PCR. NF-κB activation was measured using the dual-luciferase reporter assay.ResultsThe expression of Hes1 abolished the effects of Aβ on dendritic patterning and GABAergic input, and it prevented the death of the cultured neurons. TGFβ1, a known neuroprotector, could counteract the deleterious effects of Aβ by inducing NF-κB activation following the serine phosphorylation of I-κBα. Indeed, the number of GABAergic terminals generated by inducing Hes1 expression was doubled.ConclusionOur data define some of the mechanisms involved in Aβ-mediated cell death and they point to potential means to counteract this noxious activity.

Activation of Extracellular Signal-Regulated Protein Kinase 5 is Essential for Cystitis- and Nerve Growth Factor-Induced Calcitonin Gene-Related Peptide Expression in Sensory Neurons

BackgroundCystitis causes considerable neuronal plasticity in the primary afferent pathways. The molecular mechanism and signal transduction underlying cross talk between the inflamed urinary bladder and sensory sensitization has not been investigated.ResultsIn a rat cystitis model induced by cyclophosphamide (CYP) for 48 h, the mRNA and protein levels of the excitatory neurotransmitter calcitonin gene-related peptide (CGRP) are increased in the L6 dorsal root ganglia (DRG) in response to bladder inflammation. Cystitis-induced CGRP expression in L6 DRG is triggered by endogenous nerve growth factor (NGF) because neutralization of NGF with a specific NGF antibody reverses CGRP up-regulation during cystitis. CGRP expression in the L6 DRG neurons is also enhanced by retrograde NGF signaling when NGF is applied to the nerve terminals of the ganglion-nerve two-compartmented preparation. Characterization of the signaling pathways in cystitis- or NGF-induced CGRP expression reveals that the activation (phosphorylation) of extracellular signal-regulated protein kinase (ERK)5 but not Akt is involved. In L6 DRG during cystitis, CGRP is co-localized with phospho-ERK5 but not phospho-Akt. NGF-evoked CGRP up-regulation is also blocked by inhibition of the MEK/ERK pathway with specific MEK inhibitors U0126 and PD98059, but not by inhibition of the PI3K/Akt pathway with inhibitor LY294002. Further examination shows that cystitis-induced cAMP-responsive element binding protein (CREB) activity is expressed in CGRP bladder afferent neurons and is co-localized with phospho-ERK5 but not phospho-Akt. Blockade of NGF action in vivo reduces the number of DRG neurons co-expressing CGRP and phospho-CREB, and reverses cystitis-induced increases in micturition frequency.ConclusionsA specific pathway involving NGF-ERK5-CREB axis plays an essential role in cystitis-induced sensory activation.

Effects of RedLiriope platyphyllaon NGF secretion ability, NGF receptor signaling pathway and γ-secretase components in NSE/hAPPsw transgenic mice expressing Alzheimer's Disease

Liriope platyphylla (LP) has long been regarded as a curative herb for the treatment of diabetes, asthma, and neurodegenerative disorders. To examine the therapeutic effects of Red LP (RLP) manufactured by steaming process on neurodegenerative disorders, significant alteration of the key factors influencing Alzheimer's Disease (AD) was detected in NSE/hAPPsw transgenic (Tg) mice after RLP treatment. The concentration of nerve growth factor (NGF) in serum increased in RLP-treated NSE/hAPPsw Tg mice compared with vehicle-treated Tg mice. However, downstream effectors of the NGF receptor signaling pathway, including TrkA and p75NTR proteins, were suppressed in RLP-treated NSE/hAPPsw Tg mice. Especially, Tg mice showed decreased levels of TrkA, p75NTR, and RhoA expression. Production of Aβ-42 peptides was lower in RLP-treated NSE/hAPPsw Tg mice than in vehicle-treated Tg mice. Further, analysis of γ-secretase components showed that Aβ-42 peptide expression was downregulated. Of the four components, the expression of APH-1 and Nicastrin (NCT) decreased in RLP-treated NSE/hAPPsw Tg mice, whereas expression of PS-2 and Pen-2 was maintained or increased within the same group. Overall, these results suggest that RLP can help relieve neurodegenerative diseases, especially AD, through upregulation of NGF secretion ability, activation of NGF signaling pathway, downregulation of Aβ-42 peptide deposition, and alteration of γ-secretase components.

A Two-Dimensional ERK-AKT Signaling Code for an NGF-Triggered Cell-Fate Decision

Growth factors activate Ras, PI3K, and other signaling pathways. It is not well understood how these signals are translated by individual cells into a decision to proliferate or differentiate. Here, using single-cell image analysis of nerve growth factor (NGF)-stimulated PC12 cells, we identified a two-dimensional phospho-ERK (pERK)-phospho-AKT (pAKT) response map with a curved boundary that separates differentiating from proliferating cells. The boundary position remained invariant when different stimuli were used or upstream signaling components perturbed. We further identified Rasa2 as a negative feedback regulator that links PI3K to Ras, placing the stochastically distributed pERK-pAKT signals close to the decision boundary. This allows for uniform NGF stimuli to create a subpopulation of cells that differentiates with each cycle of proliferation. Thus, by linking a complex signaling system to a simpler intermediate response map, cells gain unique integration and control capabilities to balance cell number expansion with differentiation.

Abstract B152: Modulating the activity of nerve growth factor (NGF) and its receptors tropomyosin-related kinase A (TRKA) and p75 neurotrophin receptor (p75NTR) in perineural invasion (PNI) in pancreatic cancer.

Abstract Pancreatic cancer is the fourth leading cause of cancer-related death in the US with a 5-year survival rate of less than 5%. Even after surgery and chemotherapy, prognosis is dismal due to tumor re-occurrence. Perineural Invasion (PNI) is a process where surrounding pancreatic nerves are invaded by pancreatic cancer cells. This invasive and proliferative ability of pancreatic cancer cells is indicative of their aggressiveness and is shown to be associated with poor prognosis and pain in pancreatic cancer patients. The nerve growth factor (NGF) signaling pathway is implicated in PNI and NGF binds to a high-affinity receptor, tropomyosin kinase A (TRKA), which is differentially expressed in pancreatic tumor tissues and a low-affinity receptor, p75 neurotrophin receptor (p75NTR), whose role in PNI in pancreatic cancer is unclear. In this study, we seek to understand the molecular mechanisms of NGF regulation of PNI in pancreatic cancer. Whether NGF regulates PNI via an autocrine or paracrine manner is not well understood. Signaling via NGF-TRKA pathway induces neurites in the PC-12 neurite extension assay and conditioned media (CM) from several pancreatic cancer cell lines including BxPC3 induced neurites in this assay. Addition of an antibody to neutralize NGF in the CM or an azaoxindole inhibitor (GW441756) of TRKA resulted approximately in a 50% and 40% decrease in neurites respectively in the PC-12 assay. These results could indicate a paracrine action of NGF in promoting neurite extension in the PC-12 assay and perhaps nerve growth as related to PNI. Furthermore, knocking down the expression of NGF, p75NTR, TRKA using siRNA or inhibitor GW441756 of TRKA decreased migration of BxPC3 pancreatic cancer cells in the Boyden chamber assay by 45 − 60%. A similar inhibitory effect was observed in the movement of pancreatic cancer cells towards dorsal root ganglia (DRG) in a DRG-pancreatic cancer cell co-culture assay. Thus, NGF may function in an autocrine manner to increase proliferation and invasiveness of pancreatic cancer cells in PNI. Currently, we are working to further optimize our assays to delineate the interplay between NGF and TrkA (autocrine or paracrine) in PNI and understand the involvement of p75NTR (low-affinity NGF receptor) in NGF signaling and consequently in PNI. Understanding the molecular mechanisms involved in PNI will aid in designing novel therapeutics that prevent PNI and alleviate pain associated with PNI in patients with pancreatic cancer. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr B152.

Egr3 Dependent Sympathetic Target Tissue Innervation in the Absence of Neuron Death

Nerve Growth Factor (NGF) is a target tissue derived neurotrophin required for normal sympathetic neuron survival and target tissue innervation. NGF signaling regulates gene expression in sympathetic neurons, which in turn mediates critical aspects of neuron survival, axon extension and terminal axon branching during sympathetic nervous system (SNS) development. Egr3 is a transcription factor regulated by NGF signaling in sympathetic neurons that is essential for normal SNS development. Germline Egr3-deficient mice have physiologic dysautonomia characterized by apoptotic sympathetic neuron death and abnormal innervation to many target tissues. The extent to which sympathetic innervation abnormalities in the absence of Egr3 is caused by altered innervation or by neuron death during development is unknown. Using Bax-deficient mice to abrogate apoptotic sympathetic neuron death in vivo, we show that Egr3 has an essential role in target tissue innervation in the absence of neuron death. Sympathetic target tissue innervation is abnormal in many target tissues in the absence of neuron death, and like NGF, Egr3 also appears to effect target tissue innervation heterogeneously. In some tissues, such as heart, spleen, bowel, kidney, pineal gland and the eye, Egr3 is essential for normal innervation, whereas in other tissues such as lung, stomach, pancreas and liver, Egr3 appears to have little role in innervation. Moreover, in salivary glands and heart, two tissues where Egr3 has an essential role in sympathetic innervation, NGF and NT-3 are expressed normally in the absence of Egr3 indicating that abnormal target tissue innervation is not due to deregulation of these neurotrophins in target tissues. Taken together, these results clearly demonstrate a role for Egr3 in mediating sympathetic target tissue innervation that is independent of neuron survival or neurotrophin deregulation.

Rab22 controls NGF signaling and neurite outgrowth in PC12 cells

Rab22 is a small GTPase that is localized on early endosomes and regulates early endosomal sorting. This study reports that Rab22 promotes nerve growth factor (NGF) signaling-dependent neurite outgrowth and gene expression in PC12 cells by sorting NGF and the activated/phosphorylated receptor (pTrkA) into signaling endosomes to sustain signal transduction in the cell. NGF binding induces the endocytosis of pTrkA into Rab22-containing endosomes. Knockdown of Rab22 via small hairpin RNA (shRNA) blocks NGF-induced pTrkA endocytosis into the endosomes and gene expression (VGF) and neurite outgrowth. Overexpression of human Rab22 can rescue the inhibitory effects of the Rab22 shRNA, suggesting a specific Rab22 function in NGF signal transduction, rather than off-target effects. Furthermore, the Rab22 effector, Rabex-5, is necessary for NGF-induced neurite outgrowth and gene expression, as evidenced by the inhibitory effect of shRNA-mediated knockdown of Rabex-5. Disruption of the Rab22-Rabex-5 interaction via overexpression of the Rab22-binding domain of Rabex-5 in the cell also blocks NGF-induced neurite outgrowth, suggesting a critical role of Rab22-Rabex-5 interaction in the biogenesis of NGF-signaling endosomes to sustain the signal for neurite outgrowth. These data provide the first evidence for an early endosomal Rab GTPase as a positive regulator of NGF signal transduction and cell differentiation.

Altered norepinephrine content and ventricular function in p75NTR−/− mice after myocardial infarction

Cardiac sympathetic neurons stimulate heart rate and the force of contraction through release of norepinephrine. Nerve growth factor modulates sympathetic transmission through activation of TrkA and p75NTR. Nerve growth factor plays an important role in post-infarct sympathetic remodeling. We used mice lacking p75NTR to examine the effect of altered nerve growth factor signaling on sympathetic neuropeptide expression, cardiac norepinephrine, and ventricular function after myocardial infarction. Infarct size was similar in wildtype and p75NTR−/− mice after ischemia–reperfusion surgery. Likewise, mRNAs encoding vasoactive intestinal peptide, galanin, and pituitary adenylate cyclase activating peptides were identical in wildtype and p75NTR−/− cardiac sympathetic neurons, as was expression of the TrkA neurotrophin receptor. Norepinephrine content was elevated in the base of the p75NTR−/− ventricle compared to wildtype, but levels were identical below the site of occlusion. Left ventricular pressure, dP/dtMAX, and dP/dtMIN were measured under isoflurane anesthesia 3 and 7days after surgery. Ventricular pressure decreased significantly 3days after infarction, and deficits in dP/dtMAX were revealed by stimulating beta receptors with dobutamine and release of endogenous norepinephrine with tyramine. dP/dtMIN was not altered by genotype or surgical group. Few differences were observed between genotypes 3days after surgery, in contrast to low pressure and dP/dtMAX previously reported in control p75NTR−/− animals. Seven days after surgery ventricular pressure and dP/dtMAX were significantly lower in p75NTR−/− hearts compared to WT hearts. Thus, the lack of p75NTR did not enhance cardiac function after myocardial infarction.

Matrix Metalloproteinase-9 Participates in NGF-Induced α-Secretase Cleavage of Amyloid-β Protein Precursor in PC12 Cells

Amyloid-β protein precursor (AβPP) is a ubiquitously expressed glycoprotein, which under physiological conditions can be cleaved following two alternative routes; the non-amyloidogenic and the amyloidogenic pathway. Shift of AβPP processing in favor of the amyloidogenic pathway is a key event in the pathogenesis of Alzheimer's disease (AD). Among the factors that regulate AβPP processing, nerve growth factor (NGF) appears to play an important role; abnormal NGF signaling has been implicated in the onset of AD. In the present study, we used PC12 cells to study the effects of NGF on AβPP processing and provide evidence that NGF, through binding to its high affinity receptor, TrkA moderately down-regulates the expression of the β-secretase β-site AβPP cleaving enzyme-1 and, most importantly, upregulates the expression of two enzymes with α-secretase activity, a disintegrin and metalloprotease-17 and to a greater extent matrix metalloproteinase-9 (MMP9) in a phosphoinositide kinase-3 dependent manner. Finally, we demonstrate that MMP9 actively participates in NGF-induced α-secretase cleavage of AβPP, thus it contributes to the shift of AβPP processing towards the non-amyloidogenic pathway precluding the formation of neurotoxic Aβ peptides.

Mechanical stretch of sympathetic neurons induces VEGF expression via a NGF and CNTF signaling pathway

Mechanical stretch has been shown to increase vascular endothelial growth factor (VEGF) expression in cultured myocytes. Sympathetic neurons (SN) also possess the ability to express and secrete VEGF, which is mediated by the NGF/TrkA signaling pathway. Recently, we demonstrated that SN respond to stretch with an upregulation of nerve growth factor (NGF) and ciliary neurotrophic factor (CNTF). Whether stretch increases neuronal VEGF expression still remains to be clarified. Therefore, SN from the superior cervical ganglia of neonatal Sprangue Dawley rats were exposed to a gradual increase of stretch from 3% up to 13% within 3 days (3%, 7% and 13%). Under these conditions, the expression and secretion of VEGF was analyzed. Mechanical stretch significantly increased VEGF mRNA and protein expression (mRNA: control = 1 vs. stretch = 3.1; n = 3/protein: control = 1 vs. stretch = 2.7; n = 3). ELISA experiments to asses VEGF content in the cell culture supernatant showed a time and dose dependency in VEGF increment due to stretch. NGF and CNTF neutralization decreased stretch-induced VEGF augmentation in a significant manner. This response was mediated in part by TrkA receptor activation. The stretch-induced VEGF upregulation was accompanied by an increase in HIF-1α expression. KDR levels remained unchanged under conditions of stretch, but showed a significant increase due to NGF neutralization. In summary, SN respond to stretch with an upregulation of VEGF, which is mediated by the NGF/CNTF and TrkA signaling pathway paralleled by HIF-1α expression. NGF signaling seems to play an important role in regulating neuronal KDR expression.

Effect of hyaluronic acid on urine nerve growth factor in cyclophosphamide‐induced cystitis

To investigate how hyaluronic acid (HA) affects nerve growth factor (NGF) production and bladder overactivity in a cyclophosphamide (CYP)-induced cystitis rat model. Female Sprague-Dawley rats received three intermittent intraperitoneal injections of CYP (75 mg/kg) or saline. Before or after CYP injection, HA was given intravesically and urine NGF was checked with creatinine correction. Bladder function was evaluated by cystometrograms under Zoletil anesthesia. Furthermore, the effect of HA was counteracted with hyaluronidase (HYAL). Bladder structural change was compared among groups with trichrome stain. The intercontraction interval (ICI) significantly decreased in CYP-injected rats in comparison to the saline-injected controls. In the CYP-injected groups, bladder HA instillation significantly increased the ICI, but did not change the maximum voiding pressure in comparison to the saline instillation. NGF production significantly increased in CYP-injected rats, but decreased significantly with HA treatment. Treatment with HA had a more significant effect on urine NGF and the use of HYAL would eliminate this effect. Specific staining showed mucosa swelling after CYP treatment. Little HA coating on bladder mucosa could be found in HA-treated rats. Present findings raise the possibility that HA could be an effective treatment for CYP-related bladder overactivity through the involvement of NGF signaling.