Neurite Elongation In PC12 Cells Research Articles

25-Hydroxy Vitamin D Exhibits NGF-like Activity in PC12 Cells

Background: In our previous study, 25-hydroxy vitamin D (25OHD) supplementation was associated with improved serum vitamin D levels and, possibly, improved cognitive function. In response to nerve growth factor, PC12 cells first undergo proliferation, followed by growth arrest and differentiation. We studied the effects of 25OHD on neurite elongation in PC12 cells. Methods: PC12 cells were treated with 10ng/mL NGF with or without 6 nmol/L of 25OHD for 9 days. Phase-contrast micrographs were recorded and cells with a neurite outgrowth longer than the diameter of their cell body were counted. To investigate the expression level of Akt protein, PC12 cells were preincubated with 10ng/mL NGF with or without 6 nmol/L of 25OHD for 4 days, and lysates were assayed using a commercially available AKT/AKT ELISA kit. Results: In the presence of NGF, 25OHD induced an increase in both the number of cells with extended neurites and the length of neurites. Expression of phosphorylated Akt was enhanced by 25OHD without NGF and 25OHD up-regulated NGF-induced phosphorylation. Conclusion: These findings show that 25OHD displays NGF-mimicking and NGF-enhancing neurogenic activity in PC12 cells, which potentially depended on activating P3K/AKT signaling pathways.

Effect of Pentoxifylline on Staurosporine-Induced Neurite Elongation in PC12 Cells.

Objective:Pentoxifylline enhances neurite elongation in PC12 cells. This study investigated the effects of pentoxifylline on staurosporine-induced neurite elongation in PC12 cells. Materials and Methods:There were five treatment groups, including treatment group I (1 nM), treatment group II (10 nM), treatment group III (100 nM), treatment group IV (1uM), and treatment group V (10 mM of pentoxifylline), together with 214 nM staurosporine for a range of time (6, 12 and 24 hours). Cells only treated with staurosporine at a concentration of 214 nM were used as the control group. Cell proliferation, cell death, immunocytochemistry assay, and Total Neurite Length were assessed.Results:The results showed that pentoxifylline increased cell viability (p<0.05) in a dose- and time-dependent manner, and cell death assay showed that cell death decreased in a dose- and time-dependent manner (p<0.05). TNL increased significantly compared with control cells (p<0.05). Immunocytochemistry assay showed that pentoxifylline at low and high concentrations enhanced β-tubulin III and GFAP protein expression compared with control cells. Conclusion:It can be concluded that pentoxifylline has positive effects on the staurosporine-induced neurite outgrowth process in PC12 cells.

Neuroprotective Copper Bis(thiosemicarbazonato) Complexes Promote Neurite Elongation

Abnormal biometal homeostasis is a central feature of many neurodegenerative disorders including Alzheimer's disease (AD), Parkinson's disease (PD), and motor neuron disease. Recent studies have shown that metal complexing compounds behaving as ionophores such as clioquinol and PBT2 have robust therapeutic activity in animal models of neurodegenerative disease; however, the mechanism of neuroprotective action remains unclear. These neuroprotective or neurogenerative processes may be related to the delivery or redistribution of biometals, such as copper and zinc, by metal ionophores. To investigate this further, we examined the effect of the bis(thiosemicarbazonato)-copper complex, CuII(gtsm) on neuritogenesis and neurite elongation (neurogenerative outcomes) in PC12 neuronal-related cultures. We found that CuII(gtsm) induced robust neurite elongation in PC12 cells when delivered at concentrations of 25 or 50 nM overnight. Analogous effects were observed with an alternative copper bis(thiosemicarbazonato) complex, CuII(atsm), but at a higher concentration. Induction of neurite elongation by CuII(gtsm) was restricted to neurites within the length range of 75–99 µm with a 2.3-fold increase in numbers of neurites in this length range with 50 nM CuII(gtsm) treatment. The mechanism of neurogenerative action was investigated and revealed that CuII(gtsm) inhibited cellular phosphatase activity. Treatment of cultures with 5 nM FK506 (calcineurin phosphatase inhibitor) resulted in analogous elongation of neurites compared to 50 nM CuII(gtsm), suggesting a potential link between CuII(gtsm)-mediated phosphatase inhibition and neurogenerative outcomes.

NBS1, the Nijmegen breakage syndrome gene product, regulates neuronal proliferation and differentiation

Nijmegen breakage syndrome (NBS) is an autosomal recessive disorder, characterized by progressive microcephaly, growth retardation, immunodeficiency, and pre-disposition to tumor formation. To investigate the functions of the NBS gene product, NBS1, on neurons, PC12 cells overexpressing NBS1 and related mutants and primary cortical neuronal culture were used in the present study. Small interfering RNA (siRNA) was applied to repress the expression of endogenous Nbs1 in PC12 cells and primary cortical neurons. We demonstrated that overexpression of NBS1 increases cellular proliferation and decreases the apoptosis of PC12 cells in serum withdrawal and ionizing irradiation, through the activation of phosphatidylinositol 3-kinase (PI 3-kinase)/Akt pathway. Overexpression of NBS1 also decreases neurite elongation on PC12 cells under nerve growth factor stimulation. Transfection of NBS1-overexpressing PC12 cells with a dominant negative Akt mutant attenuates the neuroprotection and cellular proliferation effects of NBS1 while having no effect on neurite elongation. PC12 cells overexpressing NBS657del5 and NBS653 mutants, in which the major NBS1 protein in cells are truncated proteins, have decreased cellular proliferation, increased cell death, and decreased neurite elongation compared with those of control PC12 cells. Repression of Nbs1 by siRNA decreases the PI 3-kinase activity and Akt phosphorylation levels, and induces neurite elongation in PC12 cells even without nerve growth factor stimulation. Repression of Nbs1 by siRNA in primary cortical neurons also increased neurite elongation, but increased neuronal death. We conclude that NBS1 can regulate neuronal proliferation and neuroprotection via PI 3-kinase/Akt pathway while regulating neuronal differentiation in a different pathway. Excessive accumulation of truncated protein secondary to 657del5 mutation may be detrimental to neurons, leading to defective neuronal proliferation and differentiation.

Regulation of Neuronal Morphology by Toca-1, an F-BAR/EFC Protein That Induces Plasma Membrane Invagination

Actin reorganization is important for regulation of neuronal morphology. Neural Wiskott-Aldrich syndrome protein (N-WASP) is an important regulator of actin polymerization and also known to be strongly expressed in brain. Recently, Toca-1 (transducer of Cdc42-dependent actin assembly) has been shown to be required for Cdc42 to activate N-WASP from biochemical experiments. Toca-1 has three functional domains: an F-BAR/EFC domain at the N terminus, an HR1 at the center, and an SH3 domain at the C terminus. The F-BAR/EFC domain induces tubular invagination of plasma membrane, while Toca-1 binds both N-WASP and Cdc42 through the SH3 domain and the HR1, respectively. However, the physiological role of Toca-1 is completely unknown. Here we have investigated the neural function of Toca-1. Toca-1 is strongly expressed in neurons including hippocampal neurons in developing brain at early times. Knockdown of Toca-1 in PC12 cells significantly enhances neurite elongation. Consistently, overexpression of Toca-1 suppresses neurite elongation through the F-BAR/EFC domain with a membrane invaginating property, suggesting an implication of membrane trafficking in the neural function of Toca-1. In addition, knockdown of N-WASP, to our surprise, also enhances neurite elongation in PC12 cells, which is in clear contrast to the previous report that dominant negative mutants of N-WASP suppress neurite extension in PC12 cells. On the other hand, knockdown of Toca-1 in cultured rat hippocampal neurons enhances axon branching a little but not axon elongation, while knockdown of N-WASP enhances both axon elongation and branching. These results suggest that a vesicle trafficking regulator Toca-1 regulates different aspects of neuronal morphology from N-WASP.

The Inositol Polyphosphate 5-Phosphatase, PIPP, Is a Novel Regulator of Phosphoinositide 3-Kinase-dependent Neurite Elongation

The spatial activation of phosphoinositide 3-kinase (PI3-kinase) signaling at the axon growth cone generates phosphatidylinositol 3,4,5 trisphosphate (PtdIns(3,4,5)P3), which localizes and facilitates Akt activation and stimulates GSK-3beta inactivation, promoting microtubule polymerization and axon elongation. However, the molecular mechanisms that govern the spatial down-regulation of PtdIns(3,4,5)P3 signaling at the growth cone remain undetermined. The inositol polyphosphate 5-phosphatases (5-phosphatase) hydrolyze the 5-position phosphate from phosphatidylinositol 4,5 bisphosphate (PtdIns(4,5)P2) and/or PtdIns(3,4,5)P3. We demonstrate here that PIPP, an uncharacterized 5-phosphatase, hydrolyzes PtdIns(3,4,5)P3 forming PtdIns(3,4)P2, decreasing Ser473-Akt phosphorylation. PIPP is expressed in PC12 cells, localizing to the plasma membrane of undifferentiated cells and the neurite shaft and growth cone of NGF-differentiated neurites. Overexpression of wild-type, but not catalytically inactive PIPP, in PC12 cells inhibited neurite elongation. Targeted depletion of PIPP using RNA interference (RNAi) resulted in enhanced neurite differentiation, associated with neurite hyperelongation. Inhibition of PI3-kinase activity prevented neurite hyperelongation in PIPP-deficient cells. PIPP targeted-depletion resulted in increased phospho-Ser473-Akt and phospho-Ser9-GSK-3beta, specifically at the neurite growth cone, and accumulation of PtdIns(3,4,5)P3 at this site, associated with enhanced microtubule polymerization in the neurite shaft. PIPP therefore inhibits PI3-kinase-dependent neurite elongation in PC12 cells, via regulation of the spatial distribution of phospho-Ser473-Akt and phospho-Ser9-GSK-3beta signaling.

P21(ras) stimulates pathways in addition to ERK, p38, and Akt to induce elongation of neurites in PC12 cells.

Initiation and elongation of neurites in PC12 cells has been shown to be stimulated by nerve growth factor (NGF). Initiation of NGF-stimulated neurites in a PC12 subclone (PC12-N09) is rapid, giving rise to short neurites that do not elongate after 1 day. To determine whether increasing activation of p21(ras) could restore neurite elongation in these cells and whether it would affect the phosphorylation of signaling proteins, the subclone PC12-N09 was transfected with constitutively active p21(ras61L) (PC12-N09ras61L) and neurite outgrowth with or without NGF was determined. Overexpression of wild-type p21(ras) (PC12-N09rasWT) did not lead to spontaneous neurite initiation but restored the ability of NGF to stimulate continuous neurite elongation. However, NGF-stimulated phosphorylation of ERK, p38, and Akt in PC12-N09rasWT cells is similar in duration to that in PC12-N09 cells, indicating that the p21(ras) signaling through ERK, p38, and Akt was not involved in the restoration of normal neurite elongation in PC12-N09 cells. These results show that p21(ras)-activated pathways other than ERK, p38, and Akt are necessary for appropriate NGF-stimulated neurite elongation in PC12 cells.

Chimeric tumor necrosis factor-TrkA receptors reveal that ligand-dependent activation of the TrkA tyrosine kinase is sufficient for differentiation and survival of PC12 cells.

To elucidate the function of the two nerve growth factor (NGF) receptors, p75NGFR and p140trk, chimeric molecules were constructed of tumor necrosis factor (TNF) and NGF receptors. Rat PC12 pheochromocytoma cells transiently transfected with TNF-p140trk chimeras, which contain the extracellular domain of TNF receptor and the transmembrane and cytoplasmic domains of p140trk, showed TNF-dependent neuronal differentiation and cell survival. The activity of TNF-p140trk chimeras was completely blocked by the tyrosine kinase inhibitor K252a, and TNF was unable to induce neurite elongation in PC12 cells transfected with a tyrosine kinase-defective chimeric receptor. The TNF-p75NGFR chimeras, which contain the cytoplasmic domain of p75NGFR, were nonfunctional. Our results suggest that p140trk may function as ligand-activated homodimers and that ligand-mediated activation of the cytoplasmic domain of p140trk alone is sufficient for inducing a neuronal phenotype.

Increased neurite outgrowth induced by inhibition of protein tyrosine kinase activity in PC12 pheochromocytoma cells.

Genistein and other inhibitors of protein tyrosine kinases were examined for effects on neurite elongation and growth cone morphology in the rat PC12 pheochromocytoma cell line. Genistein increased the rate of neurite elongation in PC12 cells grown on a collagen/polylysine substratum after priming with nerve growth factor (NGF), but had no effect on undifferentiated cells. Steady-state levels of phosphotyrosine-modified proteins (105, 59, 52, and 46 kDa) were reduced in NGF-primed cells by genistein treatment. The target of genistein action did not appear to be the NGF receptor/trk tyrosine kinase because the presence of NGF in cultures of NGF-primed cells was not necessary for genistein-stimulated neurite outgrowth. The tyrosine kinase inhibitors tyrphostin RG508964 and herbimycin A also increased the rate of neurite elongation in NGF-primed PC12 cells. Video-enhanced differential interference contrast microscopy revealed that growth cones of genistein-treated cells had less complex morphologies and were less dynamic than untreated cells, with short filopodia restricted to the leading edge, unlike untreated cells whose growth cones exhibited longer, more numerous filopodia and lamellipodia, which remodeled continuously. These results suggest that protein tyrosine kinase activity in PC12 cells negatively regulates neurite outgrowth and directly or indirectly affects growth cone morphology.