Liquiritin potentiate neurite outgrowth induced by nerve growth factor in PC12 cells

Neurite outgrowth and neuronal differentiation play a crucial role in the development of the nervous system. Understanding of neurotrophins induced neurite outgrowth was important to develop therapeutic strategy for axon regeneration in neurodegenerative diseases as well as after various nerve injuries. It has been reported that extension of neurite and differentiation of sympathetic neuron-like phenotype was modulated by nerve growth factor (NGF) in PC12 cells. In this study, NGF mediated neurite outgrowth was investigated in PC12 cells after liquiritin exposure. Liquiritin is a kind of flavonoids that is extracted from Glycyrrhizae radix, which is frequently used to treat injury or swelling for its life-enhancing properties as well as detoxification in traditional Oriental medicine. The result showed that liquiritin significantly promotes the neurite outgrowth stimulated by NGF in PC12 cells in dose dependant manners whereas the liquiritin alone did not induce neurite outgrowth. Oligo microarray and RT-PCR analysis further clarified that the neurotrophic effect of liquiritin was related to the overexpression of neural related genes such as neurogenin 3, neurofibromatosis 1, notch gene homolog 2, neuromedin U receptor 2 and neurotrophin 5. Thus, liquiritin may be a good candidate for treatment of various neurodegenerative diseases such as Alzheimer’s disease or Parkinson’s disease.     

Reconstituted basement membrane enhances neurite outgrowth in PC12 cells induced by nerve growth factor

Rat pheochromocytoma cells (PC12) respond to nerve growth factor (NGF) by elaborating neurites. We have studied the effect of extracellular matrix proteins on responsiveness of PC12 cells to NGF. NGF elicited neurite outgrowth in cells plated on collagen, fibronectin, or laminin within 48-72 h. In contrast, cells entrapped in reconstituted basement membrane prepared from the Engelbreth-Holm-Swarm tumor (EHS-BM) responded within 24 h. Cells plated on collagen or fibronectin required a minimal dose of 50 ng/ml NGF to achieve the same effect as cells entrapped in EHS-BM at 1 ng/ml NGF. Neurites displayed by cells plated in EHS-BM were more extensively branched and remained intact up to 21 days following a single administration of NGF.     

Neuroserpin regulates neurite outgrowth in nerve growth factor-treated PC12 cells

Neuroserpin is a serine protease inhibitor widely expressed in the developing and adult nervous systems and implicated in the regulation of proteases involved in processes such as synaptic plasticity, neuronal migration and axogenesis. We have analysed the effect of neuroserpin on growth factor-induced neurite outgrowth in PC12 cells. We show that small changes in neuroserpin expression result in changes to the number of cells extending neurites and total neurite length following NGF treatment. Increased expression of neuroserpin resulted in a decrease in the number of cells extending neurites and a reduction in total free neurite length whereas reduced levels of neuroserpin led to a small increase in the number of neurite extending cells and a significant increase in total free neurite length compared to the parent cell line. Neuroserpin also altered the response of PC12 cells to bFGF and EGF treatment. Neuroserpin was localised to dense cored secretory vesicles in PC12 cells but was unable to complex with its likely enzyme target, tissue plasminogen activator at the acidic pH found in these vesicles. These data suggest that modulation of neuroserpin levels at the extending neurite growth cone may play an important role in regulating axonal growth.     

Synergistic effect of immobilized laminin and nerve growth factor on PC12 neurite outgrowth

Immobilized extracellular matrix proteins and neurotrophins have been extensively studied to enhance neuronal adhesion and proliferation on surfaces for applications in nerve tissue engineering and neuroprosthetic devices. This article describes how the coimmobilization of laminin, an extracellular matrix protein and nerve growth factor (NGF), a neurotrophin can enhance neurite outgrowth observed separately with each type of molecule. In the absence of immobilized NGF, PC12 neurite outgrowth is influenced strongly by the presence of NGF in solution and unaffected by significant increases in laminin surface density (18.7–93.5 ng/mm²). However, when both laminin and NGF are immobilized together, the surface density of laminin is an important factor in determining whether or not the neurite outgrowth‐promoting effect of NGF can be obtained. PC12 neurite outgrowth on surfaces with coimmobilized laminin and NGF with surface densities of 27.6 ng/mm² and 1.4 ng/mm², respectively, are similar to that observed on surfaces with immobilized laminin and dissolved NGF. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2009     

PC12 cells express juvenile microtubule-associated proteins during nerve growth factor-induced neurite outgrowth

Microtubule-associated proteins (MAPs) are believed to play an important role in regulating the growth of neuronal processes. The nerve growth factor-induced differentiation of PC12 pheochromocytoma cells is a widely used tissue culture model for studying this mechanism. We have found that contrary to previous suggestions, the major MAPs of adult brain, MAP1 and MAP2, are minor components of PC12 cells. Instead two novel MAPs characteristic of developing brain, MAP3 and MAP5, are present and increase more than 10-fold after nerve growth factor treatment; the timing of these increases coinciding with the bundling of microtubules and neurite outgrowth. Immunocytochemical staining showed that MAP3 and MAP5 are initially distributed throughout the cytoplasm. Subsequently MAP5 becomes associated with microtubules in both neurites and growth cones but MAP3 distribution remained diffuse. Thus MAP3 and MAP5, which are characteristic of developing neurons in the juvenile brain, are also induced in PC12 cells during neurite outgrowth in culture. In contrast MAP1, which is characteristic of mature neurons, does not increase during PC12 cell differentiation. These results provide evidence that one set of MAPs is expressed during neurite outgrowth and a different set during the maintenance of neuronal form. It also appears that the PC12 system is an appropriate model for studying the active neurite growth phase of neuronal differentiation but not for neuronal maturation.     

The role of cAMP in nerve growth factor-promoted neurite outgrowth in PC12 cells

Nerve growth factor (NGF)-mediated neurite outgrowth in rat pheochromocytoma PC12 cells has been described to be synergistically potentiated by the simultaneous addition of dibutyryl cAMP. To elucidate further the role of cAMP in NGF-induced neurite outgrowth we have used the adenylate cyclase activator forskolin, cAMP, and a set of chemically modified cAMP analogues, including the adenosine cyclic 3',5'-phosphorothioates (cAMPS) (Rp)-cAMPS and (Sp)-cAMPS. These diastereomers have differential effects on the activation of cAMP-dependent protein kinases, i.e., (Sp)-cAMPS behaves as a cAMP agonist and (Rp)-cAMPS behaves as a cAMP antagonist. Our data show that the establishment of a neuritic network, as observed from PC12 cells treated with NGF alone, could not be induced by either forskolin, cAMP, or cAMP analogues alone. The presence of NGF in combination with forskolin or cAMP or its agonistic analogues potentiated the initiation of neurite outgrowth from PC12 cells. The (Sp)-cAMPS-induced stimulation of NGF-mediated process formation was successfully blocked by the (Rp)-cAMPS diastereomer. On the other hand, NGF-stimulated neurite outgrowth was not inhibited by the presence of the cAMP antagonist (Rp)-cAMPS. We conclude that the morphological differentiation of PC12 cells stimulated by NGF does not require cAMP as a second messenger. The constant increase of intracellular cAMP, caused by either forskolin or cAMP and the analogues, in combination with NGF, not only rapidly stimulated early neurite outgrowth but also exerted a maintaining effect on the neuronal network established by NGF.     

Effects of fluvoxamine on nerve growth factor-induced neurite outgrowth inhibition by dexamethasone in PC12 cells

In the present study, we examined the effects of fluvoxamine on nerve growth factor (NGF)-induced neurite outgrowth inhibition by dexamethasone (DEX) in PC12 cells. Fluvoxamine increased NGF-induced neurite outgrowth. Compared with co-treatment with NGF and fluvoxamine, p-Akt levels were higher than the values without fluvoxamine. The phosphorylated extracellular regulated kinase 1/2 levels were slightly increased by co-treatment with NGF and fluvoxamine. Fluvoxamine concentration-dependently improved NGF-induced neurite outgrowth inhibition by DEX. Fluvoxamine also improved the decrease in the NGF-induced p-Akt level caused by DEX. Interestingly, the sigma-1 receptor antagonist NE-100 blocked the improvement effects of fluvoxamine on NGF-induced neurite outgrowth inhibition by DEX. The selective sigma-1 receptor agonist PRE-084 also improved NGF-induced neurite outgrowth inhibition by DEX, which is blocked by NE-100. These results indicate that the improvement effects of fluvoxamine on NGF-induced neurite outgrowth inhibition by DEX may be attributable to the phosphorylation of Akt and the sigma-1 receptor.     

Leukemia inhibitory factor receptor signaling negatively modulates nerve growth factor-induced neurite outgrowth in PC12 cells and sympathetic neurons

Nerve growth factor (NGF) is required for the development of sympathetic neurons and subsets of sensory neurons. Our current knowledge on the molecular mechanisms underlying the biological functions of NGF is in part based on the studies with PC12 rat pheochromocytoma cells, which differentiate into sympathetic neuron-like cells upon NGF treatment. Here we report that the expression of leukemia inhibitory factor receptor (LIFR), one of the signaling molecules shared by several neuropoietic cytokines of the interleukin-6 family, is specifically up-regulated in PC12 cells following treatment with NGF. Attenuation of LIFR signaling through stable transfection of antisense- or dominant negative-LIFR constructs enhances NGF-induced neurite extension in PC12 cells. On the contrary, overexpression of LIFR retards the growth of neurites. More importantly, whereas NGF-induced Rac1 activity is enhanced in antisense-LIFR and dominant negative-LIFR expressing PC12 cells, it is reduced in LIFR expressing PC12 cells. Following combined treatment with NGF and ciliary neurotrophic factor, sympathetic neurons exhibit attenuated neurite growth and branching. On the other hand, in sympathetic neurons lacking LIFR, neurite growth and branching is enhanced when compared with wild type controls. Taken together, our findings demonstrate that LIFR expression can be specifically induced by NGF and, besides its known function in cell survival and phenotype development, activated LIFR signaling can exert negative regulatory effects on neurite extension and branching of sympathetic neurons.     

Differential responses to nerve growth factor and epidermal growth factor in neurite outgrowth of PC12 cells are determined by Rac1 activation systems

Neurite outgrowth of PC12 cells is induced by nerve growth factor (NGF) but not by epidermal growth factor (EGF). This differential response has been explained by the duration of mitogen-activated protein kinase (MAPK) activation; NGF induces sustained MAPK activation but EGF leads short-lived activation. However, precise mechanisms have not yet been understood. Here we demonstrate the difference between NGF and EGF in regulation of Rac1, a small GTPase involved in neurite outgrowth, in PC12 cells. NGF phosphoinositide 3-kinase dependently induces transient activation of Rac1 and accumulation of active Rac1 at protrusion sites on the cell surface, inducing filamentous actin-rich protrusions and subsequent neurite formation in a Rac1-dependent manner. On the other hand, EGF phosphoinositide 3-kinase independently induces more transient Rac1 activation but neither accumulates active Rac1 nor forms Rac1- and filamentous actin-rich protrusions. Difference in the Rac1 localization between NGF and EGF was also observed with the localization of exogenously expressed green fluorescent protein-tagged Rac1. The Rac1-mediated protrusion by NGF is independent of MAPK cascade, but the subsequent neurite extension requires the cascade. Thus, the differential activation of Rac1 and localization of active Rac1 contribute to the difference in the ability of NGF and EGF to induce neurite outgrowth, and we propose that the MAPK cascade-independent prompt activation of Rac1 and recruitment of active Rac1 at the protrusion sites trigger the initiation of neurite formation.     

Temperature and pH dependence of nerve growth factor-mediated neurite outgrowth of PC12 pheochromocytoma cells

Nerve growth factor-mediated neurite outgrowth of PC12 pheochromocytoma cells was dependent on medium pH and temperature. Optimal pH was 6.8-7.1. No neurites were formed below 25 degrees C, and the number of cells having neurites increased upon elevating temperature. In contrast, the cells pretreated with nerve growth factor in suspension culture developed neurites even at 25 degrees C when they were transferred to monolayer culture. Temperature dependence of rates of the neurite formation indicates that apparent activation energy for this process is 44.6 kJ/mol.     

Synergistic effects of cyclic AMP and nerve growth factor on neurite outgrowth and microtubule stability of PC12 cells

The outgrowth of neurites from rat PC12 cells stimulated by combined treatment of nerve growth factor (NGF) with cAMP is significantly more rapid and extensive than the outgrowth induced by either factor alone. We have compared the responses of PC12 cells under three different growth conditions, NGF alone, cAMP alone, and combined treatment, with respect to surface morphology, rapidity of neurite outgrowth, and stability of neurite microtubules, to understand the synergistic action of NGF and cAMP on PC12. Surface events at early times in these growth conditions varied, suggesting divergent pathways of action of NGF and cAMP. This suggestion is strongly supported by the finding that cells exposed to saturating levels of dibutyryl cAMP without substantial neurite outgrowth initiated neurites within 5 min of NGF. This response has been adopted as a convenient assay for NGF. Neurites that regenerated in the three growth conditions showed marked differences in stability to treatments that depolymerize microtubules. The results indicate that microtubules in cells treated with both NGF and cAMP are significantly more stable than in either growth factor alone. We suggest that a shift of the assembly equilibrium favoring tubulin assembly is a necessary prerequisite for the initiation of neurites by PC12.     

Protein kinase C-epsilon plays a role in neurite outgrowth in response to epidermal growth factor and nerve growth factor in PC12 cells.

In this study, we examined the role of specific protein kinase C (PKC) isoforms in the differentiation of PC12 cells in response to nerve growth factor (NGF) and epidermal growth factor (EGF). PC12 cells express PKC-alpha, -beta, -gamma, -delta, -epsilon, -mu, and -zeta. For PKC-delta, -epsilon, and -zeta, NGF and EGF exerted differential effects on translocation. Unlike overexpression of PKC-alpha and -delta, overexpression of PKC-epsilon caused enhanced neurite outgrowth in response to NGF. In the PKC-epsilon-overexpressing cells, EGF also dramatically induced neurite outgrowth, arrested cell proliferation, and induced a sustained phosphorylation of mitogen-activated protein kinase (MAPK), in contrast to its mitogenic effects on control cells or cells overexpressing PKC-alpha and -delta. The induction of neurite outgrowth by EGF was inhibited by the MAPK kinase inhibitor PD95098. In cells overexpressing a PKC-epsilon dominant negative mutant, NGF induced reduced neurite outgrowth and a more transient phosphorylation of MAPK than in controls. Our results suggest an important role for PKC-epsilon in neurite outgrowth in PC12 cells, probably via activation of the MAPK pathway.     

Potentiation of nerve growth factor-induced neurite outgrowth in PC12 cells by a Coptidis Rhizoma extract and protoberberine alkaloids

A methanol extract of Coptidis Rhizoma effectively enhanced the outgrowth of neurite in PC12 cells induced by nerve growth factor (NGF). Following solvent partition and preparative HPLC, berberine was isolated as the major active compound. Berberine enhanced the proportion of neurite-bearing cells in a dose-dependent manner without cytotoxicity. Its structural relatives, palmatine and coptisine, showed a slightly weaker NGF-enhancing effect than berberine. These three alkaloids inhibited acetylcholinesterase activity at a level comparable to that of physostigmine, but this inhibition was not responsible for the potentiation of NGF-induced neurite outgrowth. It is demonstrated for the first time that protoberberine alkaloids potentiated the NGF-induced differentiation of neural cells.     

Effect of nerve growth factor and fibroblast growth factor on SCG10 and c-fos expression and neurite outgrowth in protein kinase C-depleted PC12 cells

The role of protein kinase C (PKC) in mediating nerve growth factor (NGF) or basic fibroblast growth factor (bFGF)-stimulated SCG10 and c-fos expression as well as neurite outgrowth was studied in PC12 cells. Activators of PKC such as phorbol 12-myristate 13-acetate (PMA) or 1-oleoyl 2-acetyl glycerol mimicked the stimulatory effect of NGF and bFGF on SCG10 mRNA levels. Induction involved a protein synthesis-dependent mechanism and was maximal within 12-24 h of exposure. Chronic treatment of the cells with PMA for up to 8 days resulted in a substantial decrease (approximately 90%) in total PKC activity in the continued presence of PMA. PKC depletion did not affect NGF- or bFGF-stimulated SCG10 mRNA induction and bFGF-stimulated c-fos mRNA induction. However, NGF-stimulated c-fos mRNA induction was attenuated. In addition, induction of neurite outgrowth was not abolished in PKC-depleted cells. The results imply that PKC is not involved in NGF- and bFGF-stimulated SCG10 mRNA induction and neurite outgrowth. Furthermore, while the effect of bFGF on c-fos mRNA induction is PKC-independent, that of NGF is mediated by PKC-dependent and -independent pathways.     

Protein deacetylase SIRT1 in the cytoplasm promotes nerve growth factor-induced neurite outgrowth in PC12 cells

SIRT1, a NAD⁺-dependent protein deacetylase, is known to have neural functions. However, despite its cytoplasmic expression in some neural cells, its cytoplasmic function, if any, is unknown. Here we found that PC12 (pheochromocytoma) cells expressed SIRT1 in the cytoplasm. Nerve growth factor (NGF)-induced neurite outgrowth of these cells was promoted by activators of SIRT1, while inhibitors of SIRT1 or SIRT1-siRNA significantly inhibited it. The overexpression of a mutant SIRT1 that localised to the cytoplasm but not the nucleus enhanced the NGF-dependent neurite outgrowth, and a cytoplasmic dominant-negative SIRT1 suppressed it. Thus, cytoplasmic SIRT1 increases the NGF-induced neurite outgrowth of PC12 cells.     

Scribble controls NGF-mediated neurite outgrowth in PC12 cells

Neurite outgrowth is mediated by dynamic changes of the cytoskeleton and is largely controlled by Rho GTPases and their regulators. Here, we show that the polarity protein Scribble controls PC12 cell neurite outgrowth in response to nerve growth factor. Scribble knockdown decreases neurite numbers and increases neurite length. This effect is linked to TrkA the cognate receptor for NGF as pharmacological inhibition of phosphorylated TrkA (pTrkA) reduces Scribble expression. Moreover, Scribble forms a complex with the MAPK components ERK1/2 in a growth factor dependent manner. In RNAi experiments where Scribble expression is efficiently depleted sustained ERK1/2 phosphorylation is reduced. Conversely, siRNA with intermediate Scribble silencing efficiency fails to match this effect indicating that ERK1/2 activation depends on basic Scribble protein levels. Finally, Scribble translocates to the plasma membrane in response to growth factor where it complexes with HRas and Rac1 suggesting that the phenotype activated by loss of Scribble may be a result of altered GTPase activity. Together, these results demonstrate a novel role for Scribble in neurite outgrowth of PC12 cells.     

Iron enhances NGF-induced neurite outgrowth in PC12 cells

Rat pheochromocytoma 12 (PC12) cells undergo neuronal differentiation in response to nerve growth factor (NGF). NGF-induced differentiation involves a number of protein kinases, including extracellular signal-regulated kinase (ERK). We studied the effect of iron on neuronal differentiation, using as model the neurite outgrowth of PC12 cells triggered by NGF when the cells are plated on collagen-coated dishes in medium containing 1% serum. The addition of iron enhanced NGF-mediated cell adhesion, spreading and neurite outgrowth. The differentiation-promoting effect of iron seems to depend on intracellular iron, since nitrilotriacetic acid (an efficient iron-uptake mediator) enhanced the response to iron. In agreement with this, intracellular, but not extracellular, iron enhanced NGF-induced neurite outgrowth in pre-spread PC12 cells, and this was correlated with increased ERK activity. Taken together, these data suggest that intracellular iron promotes NGF-stimulated differentiation of PC12 cells by increasing ERK activity.     

Schwann cells promote neurite outgrowth of dorsal root ganglion neurons through secretion of nerve growth factor

The transplantation of Schwann cells (SCs) could successfully promote axonal regeneration. This is likely to attribute to the adhesion molecules expression and growth factors secretion of SCs. But which factor(s) play a key role has not been precisely studied. In this study, an outgrowth assay using dorsal root ganglia (DRG) neuron-SC co-culture system in vitro was performed. Co-culture of SCs or application of SC-conditioned medium (CM) substantially and significantly increased DRG neurite outgrowth. Further, nerve growth factor and NGF receptor (TrkA) mRNA were highly expressed in Schwann cells and DRG neuron, respectively. The high concentration of NGF protein was detected in SC-CM. When K-252a, a specific inhibitor of NGF receptor was added, DRG neurite outgrowth was significantly decreased in a concentration-dependent manner. These data strongly suggest that SCs play important roles in neurite outgrowth of DRG neurons by secreted NGF.