Signal transduction cascades underlying de novo protein synthesis required for neuronal morphogenesis in differentiating neurons

Mesencephalic Astrocyte-Derived Neurotrophic Factor (MANF) Regulates Neurite Outgrowth Through the Activation of Akt/mTOR and Erk/mTOR Signaling Pathways

Neurite outgrowth is essential for brain development and the recovery of brain injury and neurodegenerative diseases. In this study, we examined the role of the neurotrophic factor MANF in regulating neurite outgrowth. We generated MANF knockout (KO) neuro2a (N2a) cell lines using clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 and demonstrated that MANF KO N2a cells failed to grow neurites in response to RA stimulation. Using MANF siRNA, this finding was confirmed in human SH-SY5Y neuronal cell line. Nevertheless, MANF overexpression by adenovirus transduction or addition of MANF into culture media facilitated the growth of longer neurites in RA-treated N2a cells. MANF deficiency resulted in inhibition of Akt, Erk, mTOR, and P70S6, and impaired protein synthesis. MANF overexpression on the other hand facilitated the growth of longer neurites by activating Akt, Erk, mTOR, and P70S6. Pharmacological blockade of Akt, Erk or mTOR eliminated the promoting effect of MANF on neurite outgrowth. These findings suggest that MANF positively regulated neurite outgrowth by activating Akt/mTOR and Erk/mTOR signaling pathways.

Three-dimensional brain-on-a-chip with an interstitial level of flow and its application as an in vitro model of Alzheimer's disease

There has been a growing need for in vitro models of neurodegenerative diseases such as Alzheimer's disease that would enable a better understanding of etiology and faster development of treatment strategies. However, meeting this demand has been held back by the limited ability to mimic the in vivo microenvironment in an in vitro system. Here, we developed a microfluidic chip based on three-dimensional (3D) neurospheroids that more closely mimics the in vivo brain microenvironment by providing a constant flow of fluid that is readily observed in the interstitial space of the brain. Uniform neurospheroids, with cell-cell interactions and contacts in all directions, were formed in concave microwell arrays, and a slow interstitial level of flow was maintained using an osmotic micropump system. Using this platform, we investigated the effect of flow on neurospheroid size, neural network, and neural differentiation. Neurospheroids cultured with flow were larger and formed more robust and complex neural networks than those cultured under static conditions, suggesting an effect of the interstitial level of slow and diffusion-dominant flow on continuous nutrient, oxygen, and cytokine transport and removal of metabolic wastes. We also tested the toxic effects of amyloid-β, which is generally considered to be the major contributor in Alzheimer's disease. Amyloid-β treatment via an osmotic micropump significantly reduced the viability of neurospheroids and caused a significantly more destruction of neural networks, compared to the amyloid-β treatment under static conditions. By adding in vivo-like microenvironments, we propose this 3D culture-based microfluidic chip as an in vitro brain model for neurodegenerative disease and high-throughput drug screening.

Chronic inhibition of brain phospholipase A2 in adult rats impairs the survival of newborn mature neurons in the hippocampus

Adult neurogenesis occurs in the hippocampal dentate gyrus (DG) and lateral ventricles, and includes cell proliferation and neuronal differentiation, maturation and survival. In vitro studies suggest a role for phospholipase A2 (PLA2) in neuronal differentiation/maturation and survival. This study aimed to investigate the effect of in vivo chronic inhibition of brain PLA2 in adult rats on the number of newborn mature neurons in the DG. Male Wistar rats were injected with BrdU (cell proliferation marker) and 2 weeks later (beginning of neuronal maturation) sham-operated or infused intracerebroventricularly with either vehicle (DMSO in saline) or PLA2 inhibitor (MAFP dissolved in the vehicle) for 14 days via osmotic minipump. The animals were euthanised 28 days post-BrdU and their brains immunostained for BrdU and BrdU plus NeuN (mature neuronal marker) for analysis of surviving cells. MAFP reduced the number of BrdU(+) cells in the ventral DG (p < 0.05 vs. sham; p < 0.01 vs. DMSO) and the number of BrdU(+)NeuN(+) cells in the ventral (p < 0.01 vs. sham and DMSO) and whole DG (p < 0.02 vs. sham and DMSO). There was no effect of MAFP in the dorsal DG. These findings show that chronic PLA2 inhibition in adult rat hippocampus decreases the number of newborn mature neurons in the ventral DG (reflecting in the whole DG), perhaps by impairing neuronal maturation and survival, and suggest that PLA2 inhibition reported in the hippocampus of Alzheimer disease subjects might partly contribute to the neurogenic abnormalities found in the DG in this disease.

Dual effects of Rho-kinase inhibitors on a rat model of inflammatory pain

BACKGROUND

Rho-kinases (ROCKs), a family of small GTP-dependent enzymes, are involved in a range of pain models, and their inhibition typically leads to antinociceptive effects.

OBJECTIVES

To study the effects of inhibiting ROCKs using two known inhibitors, Y27632 and HA1077 (fasudil), administered locally, on nociception and paw edema in rats.

METHODS

A range of doses of Y27632 or HA1077 (2.5 μg to 1000 μg) were injected locally into rat paws alone or in combination with carrageenan, a known proinflammatory stimulus. Nociceptive responses to mechanical stimuli and increased paw volume, reflecting edema formation, were measured at 2 h and 3 h, using a Randall-Selitto apparatus and a hydroplethysmometer, respectively.

RESULTS

Animals treated with either ROCK inhibitor showed biphasic nociceptive effects, with lower doses being associated with pronociceptive, and higher doses with antinociceptive responses. In contrast, a monophasic dose-dependent increase in edema was observed in the same animals. Local injection of 8-bromo-cyclic (c)GMP, an activator of the nitric oxide⁄cGMP⁄protein kinase G pathway, also produced biphasic effects on nociceptive responses in rat paws; however, low doses were antinociceptive and high doses were pronociceptive. Local administration of cytochalasin B, an inhibitor of actin polymerization and a downstream mediator of ROCK activity, reversed the antinociceptive effect of Y27632.

CONCLUSIONS

The results of the present study suggest that ROCKs participate in the local mechanisms associated with nociception⁄antinociception and inflammation, with a possible involvement of the nitric oxide⁄cGMP⁄protein kinase G pathway. Also, drug effects following local administration may differ markedly from the effects following systemic administration. Finally, separate treatment of pain and edema may be needed to maximize clinical benefit in inflammatory pain.

Neurogenesis recovery induced by granulocyte-colony stimulating factor in neonatal rat brain after perinatal hypoxia

BACKGROUND

Perinatal hypoxia can lead to a wide range of neurological deficits depending on the differential vulnerability of the involved brain regions to oxygen deprivation. It remains unclear whether the differential vulnerability to oxygen deprivation leads to altered neurogenesis in the neonatal brain after perinatal hypoxia. The primary objective was to investigate whether perinatal hypoxia induces deleterious changes in neurogenesis within three representative brain regions (dentate gyrus of the hippocampus, midbrain, and temporal cortex), with regards to common pathological areas clinically. The secondary objective was to investigate whether granulocyte-colony stimulating factor (G-CSF) therapy exerts beneficial effects in neurogenesis in neonatal rat brains subjected to experimental perinatal hypoxia.

MATERIALS AND METHODS

Rat pups were subjected to experimental perinatal hypoxia on the tenth day of life (P10). They were then given G-CSF (30 μg/kg, single injection/day, intraperitoneal injection, P11-16). The neurogenesis efficacy was analyzed on P17 and the radial-arm maze task, a memory task for higher cognitive functions such as problem-solving abilities, was evaluated on P37-58.

RESULTS

Perinatal hypoxia caused a significant decrease in neurogenesis within the three representative brain regions, and this deleterious outcome was alleviated by G-CSF (p < 0.05). In addition, the G-CSF therapy markedly improved the decreased performance of long-term cognitive functions induced by perinatal hypoxia (p < 0.05).

CONCLUSION

This study suggests that G-CSF may be a potentially beneficial therapy, at least in part, through universal recovery of neurogenesis effects in the neonatal brain after perinatal hypoxia insult.

Identification and functional characterization of zebrafish Gas7 gene in early development

Growth arrest-specific 7 (Gas7) is preferentially expressed in the nervous system and plays an important role during neuritogenesis in mammals. However, the structure and function of Gas7 homologs have not been studied in nonmammalian vertebrates used as models. In this report, we identify a Gas7 gene in zebrafish that we termed zfGas7. The transcript of this gene was produced by canonical splicing, and its protein product contained a Fes/CIP4 homology and a coiled-coil domain. In early zebrafish embryos, RT-PCR analyses revealed that zfGas7 was initially expressed at 5.3 hr postfertilization (hpf), followed by an increase of expression at 10 hpf and further accumulation during somitogenesis at 48 hpf. Spatiotemporal analyses further showed that Gas7 mRNA was detected in the brain, somite, and posterior presomitic mesoderm regions during somitogenesis. At 36 hpf, zfGas7 mRNA was detected in the brain and somite but was later found only in neuronal clusters of the brain at 52 hpf. Gas7 knockdown with morpholino antisense oligonucleotides (Gas7MO) reduced the number of HuC-positive neurons in the trigeminal and statoacoustic ganglions and produced deformed phenotypes, such as flattening of the top of the head. Notably, the neuron reduction and deformed phenotypes observed in Gas7MO embryos were partially rescued by ectopic expression of Gas7. Because altered somitogenesis and pigmentation were also found in the morphants, the neuronal phenotypes observed likely are due to a general developmental delay of embryogenesis. These results indicate that Gas7 is expressed in neuronal cells but is not specifically required for neuronal development in vertebrates.

Granulocyte-colony stimulating factor alleviates perinatal hypoxia-induced decreases in hippocampal synaptic efficacy and neurogenesis in the neonatal rat brain

Using various animal models, studies have greatly expanded our understanding of perinatal hypoxia-induced neuronal injury in the newborn at the cellular/molecular levels. However, the synapse-basis pathogenesis and therapeutic strategy for such detrimental alterations in the neonatal brain remain to be addressed. We investigated whether the damaged synaptic efficacy and neurogenesis within hippocampal CA1 region (an essential integration area for mammalian learning and memory) of the neonatal rat brain after perinatal hypoxia were restored by granulocyte-colony stimulating factor (G-CSF) therapy. Ten-day-old (P10) rat pups were subjected to experimentally perinatal hypoxia. G-CSF (10, 30, or 50 μg/kg, single injection/d, P11-16) was s.c. administered to neonatal rats which were analyzed on P17. Perinatal hypoxia reduced the expression in pRaf-pERK1/2-pCREB(Ser-133) signaling, the synaptic complex of postsynaptic density protein-95 (PSD-95) with N-methyl-D-aspartate receptor (NMDAR) subunits (NR1, NR2A, and NR2B), synaptic efficacy, and neurogenesis. A representatively effective dosage of G-CSF (30 μg/kg) alleviated the perinatal hypoxia-induced detrimental changes and improved the performance in long-term cognitive function. In summary, our results suggest a novel concept that synaptic efficacy defects exist in the neonatal brain previously exposed to perinatal hypoxia and that G-CSF could be a clinical potential for the synapse-basis recovery in the perinatal hypoxia suffers.

Neurite outgrowth is dependent on the association of c-Src and lipid rafts

Regulation of neurite outgrowth is an important aspect not only for proper development of the nervous system but also for tissue regeneration after nerve injury and the treatment of neuropathological conditions. Here, we report that neurite outgrowth in cortical neuron and neuro 2A (N2A) cell was dependent on intact lipid rafts, as well as the enhanced localization of c-Src in the lipid rafts. Src inhibition or lipid rafts disruption could specifically block c-Src phosphorylation profile, pY416 Src increase and pY529 Src decrease, they also resulted in pY529 Src and c-terminal Src kinase (Csk) partition out of lipid rafts. Thus, we concluded that c-Src signal cascades within the lipid rafts is crucial for efficient neurite outgrowth.

Direct binding of RalA to PKCη and its crucial role in morphological change during keratinocyte differentiation

A small G protein, RalA, was identified as a binding partner of PKCη. The binding led to activation of RalA and actin depolymerization associated with keratinocyte differentiation. These results provide new insight into the molecular mechanism of cytoskeletal regulation that leads to drastic change of cell shape.

During differentiation, keratinocytes undergo a dramatic shape change from small and round to large and flat, in addition to production of proteins necessary for the formation of epidermis. It has been shown that protein kinase C (PKC) η is crucial for keratinocyte differentiation. However, its role in this process has yet to be fully elucidated. Here, we show that catalytic activity is not necessary for enlarged and flattened morphology of human keratinocytes induced by overexpression of PKCη, although it is important for gene expression of the marker proteins. In addition, we identify the small G protein RalA as a binding partner of PKCη, which binds to the C1 domain, an indispensable region for the morphological change. The binding led activation of RalA and actin depolymerization associated with keratinocyte differentiation. siRNA techniques proved that RalA is involved in not only the keratinocyte differentiation induced by PKCη overexpression but also normal keratinocyte differentiation induced by calcium and cholesterol sulfate. These results provide a new insight into the molecular mechanism of cytoskeletal regulation leading to drastic change of cell shape.

The cyclin-dependent kinase inhibitor p57Kip2 regulates cell cycle exit, differentiation, and migration of embryonic cerebral cortical precursors

Mounting evidence indicates cyclin-dependent kinase (CDK) inhibitors (CKIs) of the Cip/Kip family, including p57(Kip2) and p27(Kip1), control not only cell cycle exit but also corticogenesis. Nevertheless, distinct activities of p57(Kip2) remain poorly defined. Using in vivo and culture approaches, we show p57(Kip2) overexpression at E14.5-15.5 elicits precursor cell cycle exit, promotes transition from proliferation to neuronal differentiation, and enhances process outgrowth, while opposite effects occur in p57(Kip2)-deficient precursors. Studies at later ages indicate p57(Kip2) overexpression also induces precocious glial differentiation, suggesting stage-dependent effects. In embryonic cortex, p57(Kip2) overexpression advances cell radial migration and alters postnatal laminar positioning. While both CKIs induce differentiation, p57(Kip2) was twice as effective as p27(Kip1) in inducing neuronal differentiation and was not permissive to astrogliogenic effects of ciliary neurotrophic factor, suggesting that the CKIs differentially modulate cell fate decisions. At molecular levels, although highly conserved N-terminal regions of both CKIs elicit cycle withdrawal and differentiation, the C-terminal region of p57(Kip2) alone inhibits in vivo migration. Furthermore, p57(Kip2) effects on neurogenesis and gliogenesis require the N-terminal cyclin/CDK binding/inhibitory domains, while previous p27(Kip1) studies report cell cycle-independent functions. These observations suggest p57(Kip2) coordinates multiple stages of corticogenesis and exhibits distinct and common activities compared with related family member p27(Kip1).

Differential roles of phospholipases A2 in neuronal death and neurogenesis: implications for Alzheimer disease

The involvement of phospholipase A(2) (PLA(2)) in Alzheimer disease (AD) was first investigated nearly 15 years ago. Over the years, several PLA(2) isoforms have been detected in brain tissue: calcium-dependent secreted PLA(2) or sPLA(2) (IIA, IIC, IIE, V, X, and XII), calcium-dependent cytosolic PLA(2) or cPLA(2) (IVA, IVB, and IVC), and calcium-independent PLA(2) or iPLA(2) (VIA and VIB). Additionally, numerous in vivo and in vitro studies have suggested the role of different brain PLA(2) in both physiological and pathological events. This review aimed to summarize the findings in the literature relating the different brain PLA(2) isoforms with alterations found in AD, such as neuronal cell death and impaired neurogenesis process. The review showed that sPLA(2)-IIA, sPLA(2)-V and cPLA(2)-IVA are involved in neuronal death, whereas sPLA(2)-III and sPLA(2)-X are related to the process of neurogenesis, and that the cPLA(2) and iPLA(2) groups can be involved in both neuronal death and neurogenesis. In AD, there are reports of reduced activity of the cPLA(2) and iPLA(2) groups and increased expression of sPLA(2)-IIA and cPLA(2)-IVA. The findings suggest that the inhibition of cPLA(2) and iPLA(2) isoforms (yet to be determined) might contribute to impaired neurogenesis, whereas stimulation of sPLA(2)-IIA and cPLA(2)-IVA might contribute to neurodegeneration in AD.

RHO GTPase signaling for axon extension: is prenylation important?

Many lines of evidence indicate the importance of the Rho family guanine nucleotide triphosphatases (GTPases) in directing axon extension and guidance. The signaling networks that involve these proteins regulate actin cytoskeletal dynamics in navigating neuronal growth cones. However, the intricate patterns that regulate Rho GTPase activation and signaling are not yet fully defined. Activity and subcellular localization of the Rho GTPases are regulated by post-translational modification. The addition of a geranylgeranyl group to the carboxy (C-) terminus targets Rho GTPases to the plasma membrane and promotes their activation by facilitating interaction with guanine nucleotide exchange factors and allowing sequestering by association with guanine dissociation inhibitors. However, it is unclear how these modifications affect neurite extension or how subcellular localization alters signaling from the classical Rho GTPases (RhoA, Rac1, and Cdc42). Here, we review recent data addressing this issue and propose that Rho GTPase geranylgeranylation regulates outgrowth.

LIM kinase mediates estrogen action on the actin depolymerization factor Cofilin

The ovarian hormone estrogen increases the axospinous synapse density in the hippocampal CA1 region of young female rats but fails to do so in aged rats. This estrogen-mediated alteration of spine synapse structures suggests the coincident requirement for the structural reorganization of the underlying actin cytoskeleton network. Actin reorganization is known to require the deactivation of Cofilin, an actin depolymerization factor. Cofilin is deactivated by LIM kinase (LIMK), and LIMK activity is modulated by the phosphorylation of specific residues. We have previously demonstrated that estrogen is able to increase phosphorylated LIMK (pLIMK) immunoreactivity (IR) in the hippocampus in vivo and that this estrogen-stimulated pLIMK-IR is decreased in the aged brain. Because Cofilin phosphorylation allows for actin filament elongation and spine synapse growth, we sought to determine if estrogen acts through Cofilin and if such estrogen action requires the observed LIMK activity. Using both hippocampal neurons and the NG108-15 neuroblastoma cell line, we demonstrate here that estrogen stimulates the phosphorylation of Cofilin in vitro. Furthermore, this estrogen action on Cofilin requires LIMK. Lastly, while initiating the phosphorylation of LIMK and Cofilin, estrogen can also stimulate the formation of filopodial extensions, an early step in the formation of nascent spines, demonstrating that estrogen can alter the actin-dependent neuronal morphology. This linkage of estrogen communication to Cofilin via LIMK provides the functionality to the age-sensitive pLIMK-IR that we have observed in vivo.

Proteomic dissection of cell type-specific H2AX-interacting protein complex associated with hepatocellular carcinoma

The replacement histone variant H2AX senses DNA double-strand breaks (DSBs) and recruits characteristic sets of proteins at its phosphorylated (gamma-H2AX) foci for concurrent DNA repair. We reasoned that the H2AX interaction network, or interactome, formed in the tumor-associated DNA DSB environment such as in hepatocellular carcinoma (HCC) cells, where preneoplastic lesions frequently occur, is indicative of HCC pathogenic status. By using an in vivo dual-tagging quantitative proteomic method, we identified 102 H2AX-specific interacting partners in HCC cells that stably expressed FLAG-tagged H2AX at close to the endogenous level. Using bioinformatics tools for data-dependent network analysis, we further found binary relationships among these interactors in defined pathway modules, implicating H2AX in a multifunctional role of coordinating a variety of biological pathways involved in DNA damage recognition and DNA repair, apoptosis, nucleic acid metabolism, Ca(2+)-binding signaling, cell cycle, etc. Furthermore, our observations suggest that these pathways interconnect through key pathway components or H2AX interactors. The physiological accuracy of our quantitative proteomic approach in determining H2AX-specific interactors was evaluated by both coimmunoprecipitation/ immunoblotting and confocal colocalization experiments performed on HCC cells. Due to their involvement in diverse functions, the H2AX interactors involved in different pathway modules, such as Poly(ADP-ribose) polymerase 1, 14-3-3 zeta, coflin 1, and peflin 1, were examined for their relative H2AX binding affinities in paired hepatocytes and HCC cells. Treatment with the DSB-inducing agent bleomycin enhanced binding of these proteins to H2AX, suggesting an active role of H2AX in coordinating the functional pathways of each protein in DNA damage recognition and repair.

Neuronal differentiation of NG108-15 cells has impact on nitric oxide- and membrane (natriuretic peptide receptor-A) cyclic GMP-generating proteins

Cyclic GMP (cGMP), produced in response to either nitric oxide (NO) or certain peptides, controls important neuronal functions. NG108-15 cells were used to characterize the expression of NO- and cGMP-generating proteins and to identify potential alterations associated with neuronal differentiation (neurite outgrowth). We find that these cells contain exclusively neuronal NO synthase (nNOS) isoforms as well as both NO- (soluble guanylyl cyclase, sGC) and natriuretic peptide- (natriuretic peptide receptor-A, NPR-A) responsive cGMP-producing enzymes. The sGC beta(1) subunit (unlike protein phosphatase 2A subunits) is highly membrane-associated. Membrane concentrations of NPR-A and nNOS, but not sGC beta(1) protein are up-regulated with neuronal differentiation. Intriguingly, the rate of hormone-induced cGMP production by NPR-A is significantly diminished in differentiated cells. These findings support roles for NPR-A, the common receptor of atrial (ANP) and B-type (BNP) natriuretic peptide in mature neurons and provide evidence for pronounced changes in neuronal submembrane cGMP signalling during neuronal differentiation.

Cofilin phosphorylation is involved in nitric oxide/cGMP-mediated nociception

There is convincing evidence that nitric oxide (NO), cGMP and cGMP-dependent protein kinase I (PKG-I) are involved in the development of hyperalgesia in response to noxious stimuli. However, downstream target proteins contributing to nociception have not been completely identified so far. Several reports indicate a role of the NO/cGMP/PKG cascade in the regulation of neurite outgrowth which is suggested to be involved in specific mechanisms of nociception. Since neurite outgrowth is strongly dependent on modulation of cytoskeleton proteins we were interested in the impact of PKG-I activation on the actin cytoskeleton and its role in inflammatory hyperalgesia. Therefore we investigated the actin-destabilising protein cofilin and its NO-dependent effects in vitro in primary neuronal cultures as well as in vivo in the zymosan-induced paw inflammation model in rats. In primary neurons from rats, treatment with the PKG-I activator 8-Br-cGMP induced a time-dependent phosphorylation of cofilin and significantly increased neurite outgrowth. Further functional analysis revealed that the underlying signal transduction pathways involve activation of the Rho-GTPases RhoA, Rac1 and Cdc42 and their corresponding downstream targets Rho-kinase (ROCK) and p21-activated kinase (PAK). In vivo, treatment of rats with the NO-synthase inhibitor l-NAME and the ROCK-inhibitor Y-27632, respectively, led to a significant decrease of cofilin phosphorylation in the spinal cord and resulted in antinociceptive effects in a model of inflammatory hyperalgesia. Our results suggest that cofilin represents a downstream target of NO/cGMP/PKG signal transduction in neurons thus indicating that it is involved in NO-mediated nociception.

Optimal neural differentiation and extension of hybrid neuroblastoma cells (NDC) for nerve-target evaluations using a multifactorial approach

In vitro models of tissues, such as the cornea, represent systems for modeling cell-to-cell interactions and tissue function. The objective of this study was to develop an optimized nerve differentiation medium to incorporate into a 3D in vitro model to study innervation and cell targeting. A hybrid neuroblastoma cell line (NDC) was examined for its ability to differentiate into neurons, produce neurites, and functionally contact target cells. Neuronal differentiation of NDCs was optimized through a combinatorial approach which involved culturing cells in the presence of various extracellular matrices and soluble factors. A serum-free medium containing nerve growth factor (NGF), dimethyl sulfoxide (DMSO), or dexamethasone resulted in the greatest proportion of NDCs demonstrating a neuronal morphology. Similarly, with supplementation of cyclic AMP (cAMP) or NGF, neurite extension was optimized. Combining these factors generated an optimized differentiation and extension medium, relative to the individual components alone. In co-culture with epithelial cells, NDC neurites generated in the optimized medium formed contacts with epithelial targets and produced substance P. Similarly, NDCs seeded into a collagen matrix produced neurites that projected through the matrix to target epithelial cells, promoted epithelial stratification, and increased the rate of epithelial wound healing. As well, differentiated NDCs could target and alter acetylcholine receptor clustering in mouse C2C12 myotubes, demonstrating synaptic plasticity. Our data supports the use of NDCs, in combination with optimized medium, for generating an innervated in vitro model.

Expression of ectodermal neural cortex 1 and its association with actin during the ovulatory process in the rat

Ectodermal neural cortex (ENC) 1, a member of the kelch family of genes, is an actin-binding protein and plays a pivotal role in neuronal and adipocyte differentiation. The present study was designed to examine the gonadotropin regulation and action of ENC1 during the ovulatory process in immature rats. The levels of ENC1 mRNA and protein were stimulated by LH/human chorionic gonadotropin (hCG) within 3 h both in vivo and in vitro. In situ hybridization analysis revealed that ENC1 mRNA was localized not only in theca/interstitial cells but also in granulosa cells of preovulatory follicles but not of growing follicles in pregnant mare's serum gonadotropin/hCG-treated ovaries. LH-induced ENC1 expression was suppressed by a high dose of protein kinase C inhibitor RO 31-8220 (10 microM) but not by low doses of RO 31-8220 (0.1-1.0 microM), suggesting the involvement of atypical protein kinase C. ENC1 was detected in both nucleus and cytoplasm that was increased by LH/hCG treatment. Both biochemical and morphological analysis revealed that LH/hCG treatment increased actin polymerization within 3 h in granulosa cells. Interestingly, ENC1 physically associated with actin and treatment with cytochalasin D, an actin-depolymerizing agent, abolished this association. Confocal microscopy further demonstrated the colocalization of ENC1 with filamentous actin (F-actin). The present study demonstrates that LH/hCG stimulates ENC1 expression and increases F-actin formation in granulosa cells. The present study further shows the physical association of ENC1 and F-actin, implicating the role of ENC1 in cytoskeletal reorganization during the differentiation of granulosa cells.

Direct Rho-associated kinase inhibition [correction of inhibiton] induces cofilin dephosphorylation and neurite outgrowth in PC-12 cells

Axons fail to regenerate in the adult central nervous system (CNS) following injury. Developing strategies to promote axonal regeneration is therapeutically attractive for various CNS pathologies such as traumatic brain injury, stroke and Alzheimer’s disease. Because the RhoA pathway is involved in neurite outgrowth, Rho-associated kinases (ROCKs), downstream effectors of GTP-bound Rho, are potentially important targets for axonal repair strategies in CNS injuries. We investigated the effects and downstream mechanisms of ROCK inhibition in promoting neurite outgrowth in a PC-12 cell model. Robust neurite outgrowth (NOG) was induced by ROCK inhibitors Y-27632 and H-1152 in a time-and dose-dependent manner. Dramatic cytoskeletal reorganization was noticed upon ROCK inhibition. NOG initiated within 5 to 30 minutes followed by neurite extension between 6 and 10 hours. Neurite processes were then sustained for over 24 hours. Rapid cofilin dephosphorylation was observed within 5 minutes of Y-27632 and H-1152 treatment. Re-phosphorylation was observed by 6 hours after Y-27632 treatment, while H-1152 treatment produced sustained cofilin dephosphorylation for over 24 hours. The results suggest that ROCK-mediated dephosphorylation of cofilin plays a role in the initiation of NOG in PC-12 cells.

Transcriptome and proteome analysis of early embryonic mouse brain development

Mouse embryonic brain development involves sequential differentiation of multipotent progenitors into neurons and glia cells. Using microarrays and large 2-DE, we investigated the mouse brain transcriptome and proteome of embryonic days 9.5, 11.5, and 13.5. During this developmental period, neural progenitor cells shift from proliferation to neuronal differentiation. As expected, we detected numerous expression changes between all time points investigated, but interestingly, the rate of alteration remained in a similar range within 2 days of development. Furthermore, up- and down-regulation of gene products was balanced at each time point which was also seen at embryonic days 16-18. We hypothesize that during embryonic development, the rate of gene expression alteration is rather constant due to limited cellular resources such as energy, space, and free water. A similar complexity in terms of expressed genes and proteins suggests that changes in relative concentrations rather than an increase in the number of gene products dominate cellular differentiation. In general, expression of metabolism and cell cycle related gene products was down-regulated when precursor cells switched from proliferation to neuronal differentiation (days 9.5-11.5), whereas neuron specific gene products were up-regulated. A detailed functional analysis revealed their implication in differentiation related processes such as rearrangement of the actin cytoskeleton as well as Notch- and Wnt-signaling pathways.

Proteomic analysis of embryonic stem cell–derived neural cells exposed to the antidepressant paroxetine

Antidepressant drugs can have significant effects on the mood of a patient suffering from major depression or other disorders. The pharmacological actions of these drugs generally affect the uptake or metabolism of the neurotransmitters serotonin, noradrenalin, and, to a lesser extent, dopamine. However, many aspects of antidepressant action are not understood. We conducted a proteomic analysis in a neuronal cell culture model in an attempt to identify molecules important to the operation of pathways functionally relevant to antidepressant action. The model involved generating cultures containing mixed neural and glial cells by controlled differentiation of mouse embryonic stem cells, followed by exposure to 1 microM paroxetine for 14 days. After antidepressant exposure, we observed increased expression or modification of sepiapterin reductase (SPR), heat shock protein 9A, RAS and EF-hand domain containing, and protein disulfide isomerase associated 3 and decreased expression or modification of creatine kinase, actin, prohibitin, a T-cell receptor alpha chain, defensin-related cryptdin 5, and the intermediate filament proteins glial fibrillary acidic protein and vimentin. SPR, the most strongly up-regulated protein observed, controls production of tetrahydrobiopterin, an essential cofactor for the synthesis of many neurotransmitters including serotonin, making it a plausible and intriguing candidate protein for involvement in mood control and antidepressant drug action. SPR and the other proteins identified may represent links to molecular processes of importance to mood dysregulation and control, and their respective genes may be novel candidates for the study of antidepressant pharmacogenetics.

Cell adhesion molecule DM-GRASP presented as nanopatterns to neurons regulates attachment and neurite growth

Adhesion and neurite formation of neurons and neuroblastoma cells critically depends on the lateral spacing of the cell adhesion molecule DM-GRASP offered as nanostructured substrate.

An NGF-induced Exo70-TC10 complex locally antagonises Cdc42-mediated activation of N-WASP to modulate neurite outgrowth

NGF-induced differentiation of PC12 cells is mediated by actin-polymerisation-driven membrane protrusion, involving GTPase signalling pathways that activate actin nucleation promoting factors such as the neural Wiskott-Aldrich syndrome protein (N-WASP). Expression of the exocyst subunit Exo70 in PC12 cells and neurons leads to the generation of numerous membrane protrusions, an effect that is strongly potentiated upon NGF-induced differentiation. Förster resonance energy transfer (FRET) imaging by fluorescence lifetime microscopy (FLIM) reveals an NGF-induced interaction of activated TC10 with Exo70. Expression of dominant-negative mutants and siRNA-mediated knockdown implicates N-WASP in NGF-induced Exo70-TC10-mediated membrane protrusion. However, FRET imaging of N-WASP activation levels of cells expressing Exo70 and/or constitutively active TC10 reveals that this complex locally antagonises the NGF-induced activation of N-WASP in membrane protrusions. Experiments involving siRNA-mediated knockdown of Cdc42 and overexpression of constitutively active Cdc42 confirm that the Exo70-TC10 complex mainly targets the NGF-induced Cdc42-dependent activation of N-WASP. Our results show that Exo70 is responsible for the correct targeting of the Exo70-TC10 complex to sites of membrane protrusion. The functional uncoupling between both pathways represents a novel regulatory mechanism that enables switching between morphologically distinct – Cdc42- or TC10-dominated – forms of cellular membrane outgrowth.

The neuropeptide pituitary adenylate cyclase-activating polypeptide exerts anti-apoptotic and differentiating effects during neurogenesis: focus on cerebellar granule neurones and embryonic stem cells

Pituitary adenylate cyclase-activating polypeptide (PACAP) was originally isolated from ovine hypothalamus on the basis of its hypophysiotrophic activity. It has subsequently been shown that PACAP and its receptors are widely distributed in the central nervous system of adult mammals, indicating that PACAP may act as a neurotransmitter and/or neuromodulator. It has also been found that PACAP and its receptors are expressed in germinative neuroepithelia, suggesting that PACAP could be involved in neurogenesis. There is now compelling evidence that PACAP exerts neurotrophic activities in the developing cerebellum and in embryonic stem (ES) cells. In particular, the presence of PACAP receptors has been demonstrated in the granule layer of the immature cerebellar cortex, and PACAP has been shown to promote survival, inhibit migration and activate neurite outgrowth of granule cell precursors. In cerebellar neuroblasts, PACAP is a potent inhibitor of the mitochondrial apoptotic pathway through activation of the MAPkinase extracellular regulated kinase. ES cells and embryoid bodies (EB) also express PACAP receptors and PACAP facilitates neuronal orientation and induces the appearance of an electrophysiological activity. Taken together, the anti-apoptotic and pro-differentiating effects of PACAP characterised in cerebellar neuroblasts as well as ES and EB cells indicate that PACAP acts not only as a neurohormone and a neurotransmitter, but also as a growth factor.

Identification of Proteomic Changes during Differentiation of Adult Mouse Subventricular Zone Progenitor Cells

The use of neural precursor cells (NPCs) represents a promising repair strategy for many neurological disorders. However, the molecular events and biological features that control NPC proliferation and their differentiation into neurons, astrocytes, and oligodendrocytes are unclear. In the present study, we used a comparative proteomics approach to identify proteins that were differentially regulated in NPCs after short-term differentiation. We also used a subcellular fractionation technique for enrichment of nuclei and other dense organelles to identify proteins that were not readily detected in whole cell extracts. In total, 115 distinct proteins underwent expression changes during NPC differentiation. Forty one of these were only identified following subcellular fractionation. These included transcription factors, RNA-processing factors, cell cycle proteins, and proteins that translocate between the nucleus and cytoplasm. Biological network analysis showed that the differentiation of NPCs was associated with significant changes in cell cycle and protein synthesis machinery. Further characterization of these proteins could provide greater insight into the mechanisms involved in regulation of neurogenesis in the adult central nervous system (CNS) and potentially identify points of therapeutic intervention.

A role of local signalling in the establishment and maintenance of the asymmetrical architecture of a neuron

Significant progress has been made in the identification of intrinsic and extrinsic factors involved in the development of nervous system. It is remarkable that the establishment and maintenance of the asymmetrical architecture of a neuron is coordinated by a limited repertoire of signalling machineries. However, the details of signalling mechanisms responsible for creating specificity and diversity required for proper development of the nervous system remain largely to be investigated. An emerging body of evidence suggests that specificity and diversity can be achieved by differential regulation of signalling components at distinct subcellular localizations. Many aspects of neuronal polarization and morphogenesis are attributed to localized signalling. Further diversity and specificity of receptor signalling can be achieved by the regulation of molecules outside the cell. Recent evidence suggests that extracellular matrix molecules are essential extrinsic cues that function to foster the growth of neurons. Therefore, it is important to understand where the signalling machineries are activated and how they are combined with other factors in order to understand the molecular mechanism underlying neuronal development.

Role of PKA in the anti-Thy-1 antibody-induced neurite outgrowth of dorsal root ganglionic neurons

Thy-1 is highly expressed in the mammalian nervous system. Our previous study showed that addition of anti-Thy-1 antibody to cultured dorsal root ganglionic (DRG) neurons promotes neurite outgrowth. In this study, we identified a novel signaling pathway mediating this event. Treatment with function-blocking anti-Thy-1 antibodies enhanced neurite outgrowth of DRG neurons in terms of total neurite length, longest neurite length, and total neurite branching points. To elucidate the possible signal transduction pathway involved, activation of kinases was evaluated by Western blotting. Transient phosphorylation of protein kinase A (PKA) and mitogen-activated kinase kinase (MEK) was induced after 15 min of anti-Thy-1 antibody treatment. Pretreatment with a PKA inhibitor (PKI) or an MEK inhibitor, PD98059, significantly decreased the neurite outgrowth response triggered by anti-Thy-1 antibody, indicating the involvement of both kinases. In addition, anti-Thy-1 antibody treatment also induced transient phosphorylation of cyclic AMP-response element-binding protein (CREB) and this effect was also blocked by a PKI or PD98059. Furthermore, the fact that PKI abolished anti-Thy-1 antibody-induced MEK phosphorylation showed that PKA acts upstream of the MEK-CREB cascade. In summary, the PKA-MEK-CREB pathway is a new pathway involved in the neurite outgrowth-promoting effect of anti-Thy-1 antibody.

Tissue-specific effects of wild-type and mutant connexin 31: a role in neurite outgrowth

Channels formed by connexins (Cx), the major protein subunits of gap junctions, allow passage of ions and molecular messengers between cells to provide a mechanism of synchronized cellular response. Twenty human Cx isoforms have been identified and mutations in the gene GJB3 encoding the 31 kDa isoform, Cx31, can cause dominant or recessive skin disease, dominant or recessive deafness or dominant neuropathy with deafness. Cx31 is expressed in differentiating keratinocytes in skin. Here, we also demonstrate endogenous Cx31 expression in human neuronal cell lines, particularly in differentiated neurones. Exogenous Cx31 expression induced neurite outgrowth in human neuronal cell lines, but not differentiation in primary human keratinocytes. Though neither the neuropathy and hearing loss mutation (66delD)Cx31 nor the skin disease associated mutation (R42P)Cx31 is able to traffic to the plasma membrane, the R42P mutant induced neurite outgrowth to a level equal to wild-type Cx31. In contrast, there was significantly reduced neurite outgrowth after (66delD)Cx31 expression. In addition to indicating a potential disease mechanism for the neuropathy/deafness mutation, this work demonstrates a tissue-specific function for Cx31.

CaMK-II modulation of GABAA receptors expressed in HEK293, NG108-15 and rat cerebellar granule neurons

The gamma-aminobutyric acid type A (GABA(A)) receptor is a pentameric ligand-gated ion channel responsible for fast synaptic inhibition in the brain. Phosphorylation of the GABA(A) receptor by serine/threonine protein kinases, at residues located in the intracellular loop between the third and fourth transmembrane domains of each subunit, can dynamically modulate receptor trafficking and function. In this study, we have assessed the effect that Ca(2+)-calmodulin-dependent protein kinase-II (CaMK-II) has on GABA(A) receptors. The intracellular application of preactivated CaMK-II failed to modulate the function of alphabeta and alphabetagamma subunit GABA(A) receptors heterologously expressed in human embryonic kidney (HEK)293 cells. However, application of similarly preactivated alpha-CaMK-II significantly potentiated the amplitudes of whole-cell GABA currents recorded from rat cultured cerebellar granule neurons and from recombinant GABA(A) receptors expressed in neuroblastoma, NG108-15, cells. The modulation by alpha-CaMK-II of current amplitude depended upon the subunit composition of GABA(A) receptors. alpha-CaMK-II potentiated GABA currents recorded from alpha1beta3 and alpha1beta3gamma2 GABA(A) receptors, but was unable to functionally modulate beta2 subunit-containing receptors. Similar results were obtained from beta2 -/- mouse cerebellar granule cell cultures and from rat granule cell cultures overexpressing recombinant alpha1beta2 or alpha1beta3 GABA(A) receptors. alpha-CaMK-II had a greater effect on the modulation of GABA responses mediated by alpha1beta3gamma2 compared with alpha1beta3 receptors, indicating a possible role for the gamma2 subunit in CaMK-II-mediated phosphorylation. In conclusion, CaMK-II can upregulate the function of GABA(A) receptors expressed in neurons or a neuronal cell line that is dependent on the beta subunit co-assembled into the receptor complex.

Regulation of chondrocyte differentiation by actin-severing protein adseverin

The importance of actin organization in controlling the chondrocyte phenotype is well established, but little is known about the cytoskeletal components regulating chondrocyte differentiation. Previously, we have observed up-regulation of an actin-binding gelsolin-like protein in hypertrophic chondrocytes. We have now identified it as adseverin (scinderin). Adseverin is drastically up-regulated during chondrocyte maturation, as shown by Northern blot analysis, in situ hybridization, and real-time RT-PCR. Its expression is positively regulated by PKC and MEK signaling as shown by inhibitory analyses. Over-expression of adseverin in non-hypertrophic chondrocytes causes rearrangement of the actin cytoskeleton, a change in cell morphology, a dramatic (3.5-fold) increase in cell volume, and up-regulation of Indian hedgehog (Ihh) and of collagen type X--all indicative of chondrocyte differentiation. These changes are mediated by ERK1/2 and p38 kinase pathways. Thus, adseverin-induced rearrangements of the actin cytoskeleton may mediate the PKC-dependent activation of p38 and Erk1/2 signaling pathways necessary for chondrocyte hypertrophy, as evidenced by changes in cell morphology, increase in cell size and expression of the chondrocyte maturation markers. These results demonstrate that interdependence of cytoskeletal organization and chondrogenic gene expression is regulated, at least in part, by actin-binding proteins such as adseverin.

Actin filament branching and protrusion velocity in a simple 1D model of a motile cell

We formulate and analyse a 1D model for the spatial distribution of actin density at the leading edge of a motile cell. The model incorporates nucleation, capping, growth and decay of actin filaments, as well as retrograde flow of the actin meshwork and known parameter values based on the literature. Using a simplified geometry, and reasonable assumptions about the biochemical processes, we derive PDEs for the density of actin filaments and their tips. Analytic travelling wave solutions are used to predict how the speed of the cell depends on rates of nucleation, capping, polymerization and membrane resistance. Analysis and simulations agree with experimental profiles for measured actin distributions. Extended versions of the model are studied numerically. We find that our model produces stable travelling wave solutions with reasonable cell speeds. Increasing the rate of nucleation of filaments (by the actin related protein Arp2/3) or the rate of actin polymerization leads to faster cell speed, whereas increasing the rate of capping or the membrane resistance reduces cell speed. We consider several variants of nucleation (spontaneous, tip, and side branching) and find best agreement with experimentally measured spatial profiles of filament and tip density in the side branching case.

The JAK3 inhibitor WHI-P154 prevents PDGF-evoked process outgrowth in human neural precursor cells

The prospect of manipulating endogenous neural stem cells to replace damaged tissue and correct functional deficits offers a novel mechanism for treating a variety of CNS disorders. The aim of this study was to investigate pathways controlling neurite outgrowth in human neural precursor cells, in particular in response to platelet-derived growth factor (PDGF). PDGF-AA, -AB and -BB were found to initiate calcium signalling and produce robust increases in neurite outgrowth. PDGF-induced outgrowth of Tuj1-positive precursors was abolished by the addition of EGTA, suggesting that calcium entry is a critical part of the signalling pathway. Wortmannin and PD098059 failed to inhibit PDGF-induced outgrowth. Clostridium Toxin B increased the amount of PDGF-induced neurite branching but had no effect on basal levels. In contrast, WHI-P154, an inhibitor of Janus protein tyrosine kinase (JAK3), Hck and Syk, prevented PDGF-induced neurite outgrowth. PDGF activates multiple signalling pathways with considerable potential for cross-talk. This study has highlighted the complexity of the pathways leading to neurite outgrowth in human neural precursors, and provided initial evidence to suggest that calcium entry is critical in producing the morphological changes observed.

Cyclin-dependent kinase 5 activators p35 and p39 facilitate formation of functional synapses

Cyclin-dependent kinase 5 (Cdk5) has emerged as a key coordinator of cell signaling in neurite outgrowth. Cdk5 needs to associate with one of the regulatory proteins p35 or p39 to be an active enzyme. To investigate if Cdk5 plays a role in the establishment of functional synapses, we have characterized the expression of Cdk5, p35, and p39 in the neuroblastoma-glioma cell line NG108-15, and recorded postsynaptic activity in myotubes in response to presynaptic overexpression of Cdk5, p35, and p39. Endogenous Cdk5 and p35 protein levels increased with cellular differentiation and preferentially distributed to soluble pools, whereas the level of p39 protein remained low and primarily was present in membrane and cytoskeletal fractions. Transient transfection of a dominant-negative mutant of Cdk5 in NG108-15 cells and subsequent culturing on differentiating muscle cells resulted in a significant reduction in synaptic activity, as measured by postsynaptic miniature endplate potentials (mEPPs). Overexpression of either Cdk5/p35 or Cdk5/p39 resulted in a substantial increase in synaptic structures that displayed postsynaptic activities, as well as mEPP frequency. These findings demonstrate that Cdk5, p35, and p39 are endogenously expressed in NG108-15 cells, exhibit distinct subcellular localizations, and that both Cdk5/p35 and Cdk5/p39 are central in formation of functional synapses.

Evidence that intracellular Ca2+ mediates the effect of α-ketoisocaproic acid on the phosphorylating system of cytoskeletal proteins from cerebral cortex of immature rats

In this study we investigated the involvement of Ca2+ on the effects of alpha-ketoisocaproic acid (KIC), the main metabolite accumulating in maple syrup urine disease (MSUD), on the phosphorylating system associated with the intermediate filament (IF) proteins in slices from cerebral cortex of 9-day-old rats. We first observed that KIC significantly decreased the in vitro phosphorylation of IF proteins in brain slices. KIC-induced dephosphorylation was mediated especially by the protein phosphatase PP2B, a Ca2+-dependent protein phosphatase, but also by PP2A. We also demonstrated the involvement of Ca2+-dependent mechanisms in the KIC effects using the specific L-voltage-dependent Ca2+ channels (L-VDCC) inhibitor nifedipine, the NMDA antagonist DL-AP5 and the intracellular Ca2+ chelator BAPTA-AM. Blockage of Ca2+ channels or chelating intracellular Ca2+ completely prevented the effects of KIC on the phosphorylating system associated to IF proteins. In addition, we verified that KIC increased 45Ca2+ uptake in brain slices after 3 and 30 min incubation. Taken together, our present data indicate that KIC increase intracellular Ca2+ levels, probably promoting the activation of calcineurin. These results might be associated with the increased dephosphorylation of the IF proteins in slices of cerebral cortex of immature rats exposed to KIC at similar concentrations from those found in blood and tissues of patients with MSUD.

Cofilin expression induces cofilin-actin rod formation and disrupts synaptic structure and function in Aplysia synapses

Cofilin-actin rods are inclusion-like structures that are induced by certain chemical or physical stresses in cultured cells, and the rods formed in neurons are thought to be associated with neurodegeneration. Here, we cloned an Aplysia cofilin homolog and overexpressed it in cultured neurons. Overexpressed cofilin formed rod-like structures that included actin. The overall neuronal morphology was unaffected by cofilin overexpression; however, a decrease in number of synaptic varicosities was observed. Consistent with this structural change by cofilin overexpression, the synaptic strength was reduced, and furthermore, the long-term facilitation elicited by repeated pulses of 5-hydroxytryptamine was impaired in sensory-to-motor synapses. However, cofilin overexpression did not induce programmed cell death. These findings suggest that the formation of cofilin-actin rod-like structures can lead to neurodegeneration, and this might be a mechanism of rundown of neuronal and synaptic function without cell death in neurodegenerative diseases.

Advancement of differentiation of oligodendrocyte progenitor cells by a cascade including protein kinase A and cyclic AMP-response element binding protein

A transcription factor, cyclic AMP-response element binding protein (CREB), which is phosphorylated by protein kinases (PKA and PKC), is known to be involved in the regulation of oligodendrocyte differentiation. However, it is still unclear whether protein kinase A (PKA) and protein kinase C (PKC) are used simultaneously or at different time points to phosphorylate CREB in oligodendrocytes and whether CREB phosphorylation advances oligodendrocyte differentiation or vise versa. Our previous experiments have shown that in the differentiation process from immature to mature cells, CREB phosphorylation depends on PKC activity and leads to the progression of differentiation. In order to gain a better understanding of the process of differentiation from progenitor to immature cells, we identified which protein kinase, i.e., PKA or PKC, regulates CREB phosphorylation and we determined whether CREB phosphorylation advances differentiation or the reverse. Our results showed that CREB phosphorylation is principally regulated by PKA activity in progenitor cells but not by PKC activity, and that this phosphorylation advances the differentiation of progenitor cells to immature cells in oligodendrocytes.

Differentiation of immature oligodendrocytes is regulated by phosphorylation of cyclic AMP-response element binding protein by a protein kinase C signaling cascade

Previous experiments showed that the expression and phosphorylation levels of cyclic AMP-response element binding protein (CREB) are important factors that regulate oligodendrocyte differentiation. The present study was designed to determine whether CREB phosphorylation advances oligodendrocyte differentiation or vice versa and to identify the protein kinase that primarily regulates CREB phosphorylation. We examined the expression and phosphorylation levels of CREB in developing oligodendrocytes at a specific differentiation stage by double-immunocytochemical staining with specific differentiation markers and antibody for phosphorylated CREB. We found that the CREB expression level increased along oligodendrocyte differentiation, and that its phosphorylated level was highest in immature oligodendrocytes. We also showed that CREB phosphorylation was regulated principally by protein kinase C (PKC) activity in immature oligodendrocytes. Our findings suggest that CREB phosphorylation is dependent on a PKC signaling cascade, and this phosphorylation activates CREB-mediated transcription and advances the differentiation of immature to mature oligodendrocytes.

Pituitary adenylate cyclase-activating polypeptide prevents the effects of ceramides on migration, neurite outgrowth, and cytoskeleton remodeling

During neuronal migration, cells that do not reach their normal destination or fail to establish proper connections are eliminated through an apoptotic process. Recent studies have shown that the proinflammatory cytokine tumor necrosis factor alpha (and its second messengers ceramides) and the neuropeptide pituitary adenylate cyclase-activating polypeptide (PACAP) play a pivotal role in the histogenesis of the cerebellar cortex. However, the effects of ceramides and PACAP on migration of cerebellar granule cells have never been investigated. Time-lapse videomicroscopy recording showed that C2-ceramide, a cell-permeable ceramide analog, and PACAP induced opposite effects on cell motility and neurite outgrowth. C2-ceramide markedly stimulated cell movements during the first hours of treatment and inhibited neuritogenesis, whereas PACAP reduced cell migration and promoted neurite outgrowth. These actions of C2-ceramide on cell motility and neurite outgrowth were accompanied by a disorganization of the actin filament network, depolarization of tubulin, and alteration of the microtubule-associated protein Tau. In contrast, PACAP strengthened the polarization of actin at the emergence cone, increased Tau phosphorylation, and abolished C2-ceramide-evoked alterations of the cytoskeletal architecture. The caspase-inhibitor Z-VAD-FMK, like PACAP, suppressed the "dance of the death" provoked by C2-ceramide. Finally, Z-VAD-FMK and the PP2A inhibitor okadaic acid both prevented the impairment of Tau phosphorylation induced by C2-ceramide. Taken together, these data indicate that the reverse actions of C2-ceramide and PACAP on cerebellar granule cell motility and neurite outgrowth are attributable to their opposite effects on actin distribution, tubulin polymerization, and Tau phosphorylation.