Induction of serpinb1a by PACAP or NGF is required for PC12 cells survival after serum withdrawal

Changes in the Dentate Gyrus Gene Expression Profile Induced by Levetiracetam Treatment in Rats with Mesial Temporal Lobe Epilepsy

Temporal lobe epilepsy (TLE) is one of the most common forms of focal epilepsy. Levetiracetam (LEV) is an antiepileptic drug whose mechanism of action at the genetic level has not been fully described. Therefore, the aim of the present work was to evaluate the relevant gene expression changes in the dentate gyrus (DG) of LEV-treated rats with pilocarpine-induced TLE. Whole-transcriptome microarrays were used to obtain the differential genetic profiles of control (CTRL), epileptic (EPI), and EPI rats treated for one week with LEV (EPI + LEV). Quantitative RT-qPCR was used to evaluate the RNA levels of the genes of interest. According to the results of the EPI vs. CTRL analysis, 685 genes were differentially expressed, 355 of which were underexpressed and 330 of which were overexpressed. According to the analysis of the EPI + LEV vs. EPI groups, 675 genes were differentially expressed, 477 of which were downregulated and 198 of which were upregulated. A total of 94 genes whose expression was altered by epilepsy and modified by LEV were identified. The RT-qPCR confirmed that LEV treatment reversed the increased expression of Hgf mRNA and decreased the expression of the Efcab1, Adam8, Slc24a1, and Serpinb1a genes in the DG. These results indicate that LEV could be involved in nonclassical mechanisms involved in Ca2+ homeostasis and the regulation of the mTOR pathway through Efcab1, Hgf, SLC24a1, Adam8, and Serpinb1a, contributing to reduced hyperexcitability in TLE patients.

The Heterogeneity of Response of PC12 Cells from Different Laboratories to Nerve Growth Factor and Pituitary Adenylate Cyclase-Activating Polypeptide Questions the Reproducibility of Studies Carried Out with Tumor Cell Lines

BACKGROUND

PC12 pheochromocytoma tumor cell lines are widely used to decipher the intracellular signaling mechanisms mediating the effects of some growth factors. Nevertheless, the disparity in appearance of some PC12 cell lines used in the different publications questions our ability to compare the results obtained by the numerous laboratories which use them. This led us to analyze the phenotypic aspect and transcriptomic expression of 5 PC12 cell lines from different origins under control conditions and after treatment with nerve growth factor (NGF) or pituitary adenylate cyclase-activating polypeptide (PACAP).

METHODS

Characterization of the 5 PC12 cell lines was conducted using imaging techniques and high-throughput real-time PCR combined with bioinformatics analysis.

RESULTS

The results show that the 5 cell lines are very variable in terms of shape, proliferation rate, motility, adhesion to the substrate, and gene expression. This high heterogeneity of the cell lines is also found when looking at their response to NGF or PACAP on gene expression or differentiation, with even in some cases opposite effects, as, for example, on cell proliferation. Actually, only 2 of the cell lines tested exhibited some phenotypic similarities with each other, even though the transcriptomic analyses show that they are far from identical.

DISCUSSION/CONCLUSION

As this issue of cell heterogenicity is not restricted to PC12 cells, the present results highlight the need to facilitate the supply of cell lines at low cost, the necessity to standardize practices regarding the use of cell lines, and the requirement to define precise markers of established cell lines which should be monitored in every publication. Regarding this latter point, the present data show that transcriptomic analysis by real-time PCR using a panel of genes of interest is easy to implement and provides a reliable method to control the possible drift of the cells over time in culture. Transcriptomic phenotyping combined with bioinformatics analysis can also be a useful approach to predict the response of the cells to treatments in terms of cell signaling activation, which can help to choose among several cell lines the most appropriate one for the investigation of a particular mechanism. Taken together, the results from this study highlight the need to use well-characterized cell lines with standardized protocols to generate reproducible results from 1 laboratory to the other.

ERK-dependent induction of the immediate-early gene Egr1 and the late gene Gpr50 contribute to two distinct phases of PACAP Gs-GPCR signaling for neuritogenesis

Gs-coupled GPCR-stimulated neuritogenesis in PC12 and NS-1 - cells depends on activation of the MAP kinase ERK. Here, we examine changes in ERK activation (phosphorylation), and the time course of ERK-dependent gene induction, to seek transcriptional determinants for this process. Quenching of ERK activation by inhibition of MEK with U0126 at any time point for at least 24 h following addition of PACAP resulted in arrest of neurite formation. Changes in the transcriptome profile throughout this time period revealed at least two phases of gene induction: an early phase dominated by induction of immediate-early genes, and a later phase of gene induction after 4-6 h of exposure to PACAP with persistent elevation of phospho-ERK levels. Genes induced by PACAP in both phases consisted in those whose induction was dependent on ERK (i.e., blocked by U0126), and some whose induction was blocked by the protein kinase A inhibitor H89. ERK-dependent "late gene" transcripts included Gpr50, implicated earlier in facilitation of NGF-induced neurite formation in NS-1 cells. Gpr50 induction by PACAP, but not NGF, was dependent on the guanine nucleotide exchange factor RapGEF2, which has been shown to be required for PACAP-induced neuritogenesis in NS-1 cells. Expression of a Gpr50-directed shRNA lowered basal levels of Gpr50 mRNA and attenuated Gpr50 mRNA and GPR50 protein induction by PACAP, with a corresponding attenuation of PACAP-induced neuritogenesis. Gs-GPCR-stimulated neuritogenesis first requires immediate-early gene induction, including that of Egr1 (Zif268/NGF1A/Krox24) as previously reported. This early phase of gene induction, however, is insufficient to maintain the neuritogenic process without ERK-dependent induction of additional late genes, including Gpr50, upon continuous exposure to neurotrophic neuropeptide. Early (Egr1) and late (Gpr50) gene induction by NGF, like that for PACAP, was inhibited by U0126, but was independent of RapGEF2, confirming distinct modes of ERK activation by Gs-coupled GPCRs and neurotrophic tyrosine receptor kinases, converging on a final common ERK-dependent signaling pathway for neuritogenesis.

CREB3L2 Modulates Nerve Growth Factor-Induced Cell Differentiation

Nerve growth factor (NGF) stimulates numerous cellular physiological processes, including growth, differentiation, and survival, and maintains the phenotype of several neuronal types. Most of these NGF-induced processes require adaptation of the secretory pathway since they involve extensive remodeling of membranes and protein redistribution along newly formed neuritic processes. CREB3 transcription factors have emerged as signaling hubs for the regulation of numerous genes involved in the secretory pathway and Golgi homeostasis, integrating stimuli from multiple sources to control secretion, posttranslational modifications and trafficking of proteins. Although recent studies have focused on their role in the central nervous system, little is known about their participation in cell differentiation. Therefore, we aimed to analyze the expression and signaling mechanism of CREB3 transcription factor family members, using the NGF-induced PC12 cell differentiation model. Results show that NGF treatment causes Golgi enlargement and a parallel increased expression of proteins and mRNAs encoding for proteins required for membrane transport (transport factors). Additionally, a significant increase in CREB3L2 protein and mRNA levels is detected in response to NGF. Both MAPK and cAMP signaling pathways are required for this response. Interestingly, CREB3L2 overexpression hampers the NGF-induced neurite outgrowth while its inhibition enhances the morphological changes driven by NGF. In agreement, CREB3L2 overexpressing cells display higher immunofluorescence intensity of Rab5 GTPase (a negative regulator of PC12 differentiation) than control cells. Also, Rab5 immunofluorescence levels decrease in CREB3L2-depleted cells. Taken together, our findings imply that CREB3L2 is an important downstream effector of NGF-activated pathways, leading to neuronal differentiation.

Dysregulated autophagy is linked to BAX oligomerization and subsequent cytochrome c release in 6-hydroxydopmaine-treated neuronal cells

Autophagy and apoptosis are essential physiological pathways that are required to maintain cellular homeostasis. Therefore, it is suggested that dysregulation in both pathways is linked to several disease states. Moreover, the crosstalk between autophagy and apoptosis plays an important role in pathophysiological processes associated with several neurodegenerative disorders. We have previously reported that 6-hydroxydopamine (6-OHDA)-triggered reactive oxygen species (ROS) induces dysregulated autophagy, and that a dysregulated autophagic flux contributes to caspase-dependent neuronal apoptosis. Based on our previous findings, we specifically aimed to elucidate the molecular mechanisms underlying the potential role of dysregulated autophagy in apoptotic neurodegeneration. The disuccinimidyl suberate (DSS) cross-linking assay and immunological analyses indicated that exposure of several types of cells to 6-OHDA resulted in BAX activation and subsequent oligomerization. Pharmacological inhibition and genetic perturbation of autophagy prevented 6-OHDA-induced BAX oligomerization and subsequent release of mitochondrial cytochrome c into the cytosol and caspase activation. These events were independent of expression levels of XIAP. Taken together, our results suggest that BAX oligomerization comprises a critical step by which 6-OHDA-induced dysregulated autophagy mediates neuronal apoptosis.

Protective Effects of Pituitary Adenylate Cyclase-Activating Polypeptide and Vasoactive Intestinal Peptide Against Cognitive Decline in Neurodegenerative Diseases

Cognitive impairment is one of the major symptoms in most neurodegenerative disorders such as Alzheimer’s (AD), Parkinson (PD), and Huntington diseases (HD), affecting millions of people worldwide. Unfortunately, there is no treatment to cure or prevent the progression of those diseases. Cognitive impairment has been related to neuronal cell death and/or synaptic plasticity alteration in important brain regions, such as the cerebral cortex, substantia nigra, striatum, and hippocampus. Therefore, compounds that can act to protect the neuronal loss and/or to reestablish the synaptic activity are needed to prevent cognitive decline in neurodegenerative diseases. Pituitary adenylate cyclase-activating polypeptide (PACAP) and vasoactive intestinal peptide (VIP) are two highly related multifunctional neuropeptides widely distributed in the central nervous system (CNS). PACAP and VIP exert their action through two common receptors, VPAC1 and VPAC2, while PACAP has an additional specific receptor, PAC1. In this review article, we first presented evidence showing the therapeutic potential of PACAP and VIP to fight the cognitive decline observed in models of AD, PD, and HD. We also reviewed the main transduction pathways activated by PACAP and VIP receptors to reduce cognitive dysfunction. Furthermore, we identified the therapeutic targets of PACAP and VIP, and finally, we evaluated different novel synthetic PACAP and VIP analogs as promising pharmacological tools.

Cancer Stem Cells: Emergent Nature of Tumor Emergency

A functional analysis of 167 genes overexpressed in Krebs-2 tumor initiating cells was performed. In the first part of the study, the genes were analyzed for their belonging to one or more of the three groups, which represent the three major phenotypic manifestation of malignancy of cancer cells, namely (1) proliferative self-sufficiency, (2) invasive growth and metastasis, and (3) multiple drug resistance. 96 genes out of 167 were identified as possible contributors to at least one of these fundamental properties. It was also found that substantial part of these genes are also known as genes responsible for formation and/or maintenance of the stemness of normal pluri-/multipotent stem cells. These results suggest that the malignancy is simply the ability to maintain the stem cell specific genes expression profile, and, as a consequence, the stemness itself regardless of the controlling effect of stem niches. In the second part of the study, three stress factors combined into the single concept of "generalized cellular stress," which are assumed to activate the expression of these genes, were defined. In addition, possible mechanisms for such activation were identified. The data obtained suggest the existence of a mechanism for the de novo formation of a pluripotent/stem phenotype in the subpopulation of "committed" tumor cells.

Nerve Growth Factor (NGF)-Receptor Survival Axis in Head and Neck Squamous Cell Carcinoma

Neurotrophins and their receptors might regulate cell survival in head and neck squamous cell carcinoma (HNSCC). mRNA expression of nerve growth factor (NGF) and protein synthesis of high (NTRK1) and low affinity neurotrophin (p75 neurotrophin receptor; NTR) receptors were investigated in normal oral mucosa and in HNSCC. HNSCC cell lines were treated with mitomycin C (MMC) and cell survival was investigated. Normal and malignant epithelial cells expressed NGF mRNA. NTRK1 was upregulated in 80% of HNSCC tissue, and 50% of HNSCC samples were p75NTR positive. Interestingly, in HNSCC tissue: NTRK1 and p75NTR immunohistochemical reactions were mutually exclusive. Detroit 562 cell line contained only p75NTR, UPCI-SCC090 cells synthesized NTRK1 but not p75NTR and SCC-25 culture had p75NTR and NTRK1 in different cells. NGF (100 ng/mL) significantly improved (1.4-fold) the survival of cultured UPCI-SCC090 cells after MMC-induced cell cycle arrest, while Detroit 562 cells with high levels of p75NTR did not even get arrested by single short MMC treatment. p75NTR in HNSCC might be related with NGF-independent therapy resistance, while NTRK1 might transduce a survival signal of NGF and contribute in this way to improved tumor cell survival after cell cycle arrest.

PACAP Protects the Adolescent and Adult Mice Brain from Ethanol Toxicity and Modulates Distinct Sets of Genes Regulating Similar Networks

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a 38-amino acid neuropeptide which has been shown to exert various neuroprotective actions in vitro and in vivo; however, the ability of endogenous PACAP to prevent cell death in vivo remains to be elucidated. To explore the capacity of endogenous PACAP to prevent ethanol toxicity, adolescent and adult PACAP knockout (KO) mice were injected with ethanol in a binge drinking-like manner. Biochemical analyses revealed that ethanol administration induced an increase in the production of reactive oxygen species and the activity of caspase-3 in PACAP KO mice in an age-independent manner. In order to characterize the mechanisms underlying the sensitivity of PACAP KO mice, a whole-genome microarray analysis was performed to compare gene regulations induced by ethanol in adolescent and adult wild-type and PACAP KO mice. Gene expression substantially differed between adolescent and adult wild-type mice, suggesting distinct effects of ethanol according to the state of brain maturation. Interestingly, in adolescent and adult PACAP KO mice, the set of genes regulated were also markedly different but seemed to inhibit some similar regulatory network processes associated in particular with DNA repair and cell cycle. These data imply that ethanol induces serious DNA damages and cell cycle alteration in PACAP KO mice. This hypothesis, based on the transcriptomic data, could be confirmed by functional studies which showed that cell proliferation decreased in adolescent and adult PACAP KO mice treated with ethanol but recovered after a 30-day withdrawal period. These data, obtained with PACAP KO animals, demonstrate that endogenous PACAP protects the brain of adolescent and adult mice from alcohol toxicity and modulates distinct sets of genes according to the maturation status of the brain.