Riluzole-induced glial cell line-derived neurotrophic factor production is regulated through fibroblast growth factor receptor signaling in rat C6 glioma cells

Small-Molecule-Driven Direct Reprogramming of Fibroblasts into Functional Sertoli-Like Cells as a Model for Male Reproductive Toxicology

Sertoli cells (SCs) are vital to providing morphological and nutritional support for spermatogenesis. Defects in SCs often lead to infertility. SCs transplantation is a promising potential strategy to compensate for SC dysfunction. However, isolation of SCs from testes is impractical due to obvious and ethical limitations. Here, a molecular cocktail is identified comprising of pan-BET family inhibitor (I-BET151), retinoic acid, and riluzole that enables the efficient conversion of fibroblasts into functional Sertoli-like cells (CiSCs). The gene expression profiles of CiSCs resemble those of mature SCs and exhibit functional properties such as the formation of testicular seminiferous tubules, engulfment of apoptotic sperms, supporting the survival of germ cells, and suppressing proliferation of primary lymphocytes in vitro. Moreover, CiSCs are sensitive to toxic substances, making them an alternative model to study the deleterious effects of toxicants on SCs. The study provides an efficient approach to reprogram fibroblasts into functional SCs by using pure chemical compounds.

Iboga Inspired N-Indolylethyl-Substituted Isoquinuclidines as a Bioactive Scaffold: Chemoenzymatic Synthesis and Characterization as GDNF Releasers and Antitrypanosoma Agents

The first stage of the drug discovery process involves the identification of small compounds with biological activity. Iboga alkaloids are monoterpene indole alkaloids (MIAs) containing a fused isoquinuclidine-tetrahydroazepine ring. Both the natural products and the iboga-inspired synthetic analogs have shown a wide variety of biological activities. Herein, we describe the chemoenzymatic preparation of a small library of novel N-indolylethyl-substituted isoquinuclidines as iboga-inspired compounds, using toluene as a starting material and an imine Diels-Alder reaction as the key step in the synthesis. The new iboga series was investigated for its potential to promote the release of glial cell line-derived neurotrophic factor (GDNF) by C6 glioma cells, and to inhibit the growth of infective trypanosomes. GDNF is a neurotrophic factor widely recognized by its crucial role in development, survival, maintenance, and protection of dopaminergic neuronal circuitries affected in several neurological and psychiatric pathologies. Four compounds of the series showed promising activity as GDNF releasers, and a leading structure (compound 11) was identified for further studies. The same four compounds impaired the growth of bloodstream Trypanosoma brucei brucei (EC₅₀ 1-8 μM) and two of them (compounds 6 and 14) showed a good selectivity index.

Crosstalk between DNA methylation and histone acetylation triggers GDNF high transcription in glioblastoma cells

BACKGROUND

Glial cell line-derived neurotrophic factor (GDNF) is highly expressed in glioblastoma (GBM) and blocking its expression can inhibit the initiation and development of GBM. GDNF is a dual promoter gene, and the promoter II with two enhancers and two silencers plays a major role in transcription initiation. We had previously reported that histone hyperacetylation and DNA hypermethylation in GDNF promoter II region result in high transcription of GDNF in GBM cells, but the mechanism remains unclear. In this study, we investigated whether these modifications synergistically regulate high GDNF transcription in GBM.

RESULTS

Cyclic AMP response element binding protein (CREB) expression and phosphorylation at S133 were significantly increased in human GBM tissues and GBM cell lines (U251 and U343). In U251 GBM cells, high expressed CREB significantly enhanced GDNF transcription and promoter II activity. CREB regulated GDNF transcription via the cyclic AMP response elements (CREs) in enhancer II and silencer II of GDNF promoter II. However, the two CREs played opposite regulatory roles. Interestingly, hypermethylation of CRE in silencer II occurred in GBM tissues and cells which led to decreased and increased phosphorylated CREB (pCREB) binding to silencer II and enhancer II, respectively. Moreover, pCREB recruited CREB binding protein (CBP) with histone acetylase activity to the CRE of GDNF enhancer II, thereby increasing histone H3 acetylation and RNA polymerase II recruitment there and at the transcription start site (TSS), and promoted GDNF high transcription in U251 cells. The results indicated that high GDNF transcription was attributable to DNA hypermethylation in CRE of GDNF silencer II increasing pCREB binding to CRE in enhancer II, which enhanced CBP recruitment, histone H3 acetylation, and RNA polymerase II recruitment there and at the TSS.

CONCLUSIONS

Our results demonstrate that pCREB-induced crosstalk between DNA methylation and histone acetylation at the GDNF promoter II enhanced GDNF high transcription, providing a new perspective for GBM treatment.

New insights into Wnt signaling alterations in amyotrophic lateral sclerosis: a potential therapeutic target?

Amyotrophic lateral sclerosis is a fatal neurodegenerative disorder characterized by upper and lower motor neuron degeneration, which leads to progressive paralysis of skeletal muscles and, ultimately, respiratory failure between 2–5 years after symptom onset. Unfortunately, currently accepted treatments for amyotrophic lateral sclerosis are extremely scarce and only provide modest benefit. As a consequence, a great effort is being done by the scientific community in order to achieve a better understanding of the different molecular and cellular processes that influence the progression and/or outcome of this neuropathological condition and, therefore, unravel new potential targets for therapeutic intervention. Interestingly, a growing number of experimental evidences have recently shown that, besides its well-known physiological roles in the developing and adult central nervous system, the Wnt family of proteins is involved in different neuropathological conditions, including amyotrophic lateral sclerosis. These proteins are able to modulate, at least, three different signaling pathways, usually known as canonical (β-catenin dependent) and non-canonical (β-catenin independent) signaling pathways. In the present review, we aim to provide a general overview of the current knowledge that supports the relationship between the Wnt family of proteins and its associated signaling pathways and amyotrophic lateral sclerosis pathology, as well as their possible mechanisms of action. Altogether, the currently available knowledge suggests that Wnt signaling modulation might be a promising therapeutic approach to ameliorate the histopathological and functional deficits associated to amyotrophic lateral sclerosis, and thus improve the progression and outcome of this neuropathology.

Induction of glial cell line-derived neurotrophic factor by the squamosamide derivative FLZ in astroglia has neuroprotective effects on dopaminergic neurons

Glial cell line-derived neurotrophic factor (GDNF) has neurotrophic activity for the survival of dopaminergic neurons, which is under active investigation for Parkinson's disease (PD) therapy. FLZ is a potential new drug for PD treatment. However, it is unclear whether neurotrophic activity contributes to the neuroprotective effects of FLZ. Here we found that FLZ markedly improved the function of dopaminergic neurons in primary mesencephalic neuron/glia cultures. Further investigation demonstrated that astroglia were required for FLZ to function as a neurotrophic regulator, as FLZ failed to show neurotrophic effects in the absence of astroglia. We clarified that GDNF was responsible for the neurotrophic effects of FLZ since FLZ selectively stimulated GDNF production, which was confirmed by the finding that the neurotrophic effect of FLZ was attenuated by GDNF-neutralizing antibody. Mechanistic study demonstrated that GDNF induction by FLZ was CREB-dependent and that PI3K/Akt was the main pathway regulating CREB activity, which was confirmed by in vivo studies. We also validated that the induction of GDNF by FLZ contributed to PD treatment in vivo. In conclusion, the present data provided evidence that FLZ had robust neurotrophic effects on dopaminergic neurons through sustained induction of GDNF in astroglia by activating the PI3K/Akt/CREB pathway.

The glutamate release inhibitor riluzole increases DNA damage and enhances cytotoxicity in human glioma cells, in vitro and in vivo

Purpose

High-grade gliomas are lethal malignancies that cause morbidity and mortality due to local progression rather than metastatic spread. Our group has previously demonstrated that human GRM1 (hGRM1) is ectopically expressed in melanocytes leading to a transformed phenotype. Riluzole, a glutamate release inhibitor, leads to apoptotic cell death via DNA damage. Recent work has demonstrated the pathological significance of the related mGluR3/GRM3 (protein or gene: hGRM3) in gliomas. We evaluated the effect of riluzole on glioma cells.

Experimental Design

Western blot analysis and immunofluorescence was performed to assess for GRM3 expression in commercially available and patient-derived glioma cells and for functional analysis of GRM3 using receptor agonist/antagonists and downstream effectors, ERK and AKT phosphorylation, as the read-out. Glutamate secretion by glioma cells was measured using ELISA. Flank and intracranial mouse xenograft models were used to assess growth delay with the glutamate release inhibitor, riluzole (RIL). Immunofluorescence was used to evaluate 53BP1 or γ-H2AX foci after RIL.

Results

GRM3 was expressed in most tested glioma samples, and strongly expressed in some. Glioma cells were found to secrete glutamate in the extracellular space and to respond to receptor stimulation by activating downstream ERK. This signaling was abrogated by pretreatment with RIL. Treatment with RIL caused an increase in DNA damage markers, and an increase in cellular cytotoxicity in vitro and in vivo.

Conclusions

We have demonstrated that pretreatment with the glutamate-release inhibitor riluzole sensitizes glioma cells to radiation and leads to greater cytotoxicity; these results have clinical implications for patients with glioblastoma.

Role of glial cell line-derived neurotrophic factor in the pathogenesis and treatment of mood disorders

Glial cell line-derived neurotrophic factor (GDNF) is widely recognized as a survival factor for dopaminergic neurons, but GDNF has also been shown to promote development, differentiation, and protection of other central nervous system neurons and was thought to play an important role in various neuropsychiatric disorders. Severe mood disorders, such as primarily major depressive disorder and bipolar affective disorder, attract particular attention. These psychopathologies are characterized by structural alterations accompanied by the dysregulation of neuroprotective and neurotrophic signaling mechanisms required for the maturation, growth, and survival of neurons and glia. The main objective of this review is to summarize the recent findings and evaluate the potential role of GDNF in the pathogenesis and treatment of mood disorders. Specifically, it describes (1) the implication of GDNF in the mechanism of depression and in the effect of antidepressant drugs and mood stabilizers and (2) the interrelation between GDNF and brain neurotransmitters, playing a key role in the pathogenesis of depression. This review provides converging lines of evidence that (1) brain GDNF contributes to the mechanism underlying depressive disorders and the effect of antidepressants and mood stabilizers and (2) there is a cross-talk between GDNF and neurotransmitters representing a feedback system: GDNF-neurotransmitters and neurotransmitters-GDNF.

Targeting astrocytes in major depression

Astrocytes represent a highly heterogeneous population of neural cells primarily responsible for the homeostasis of the CNS. Astrocytes express multiple receptors for neurotransmitters, including the serotonin 5-HT2B receptors and interact with neurones at the synapse. Astroglia contribute to neurological diseases through homeostatic response, neuroprotection and reactivity. In major depression, astrocytes show signs of degeneration and are decreased in numbers, which may lead to a misbalance in neurotransmission and aberrant synaptic connectivity. In this review, we summarize astroglia-specific effects of major antidepressants and outline future strategies for astroglia-specific therapy in neuropsychiatric disorders.

Researching glutamate - induced cytotoxicity in different cell lines: a comparative/collective analysis/study

Although glutamate is one of the most important excitatory neurotransmitters of the central nervous system, its excessive extracellular concentration leads to uncontrolled continuous depolarization of neurons, a toxic process called, excitotoxicity. In excitotoxicity glutamate triggers the rise of intracellular Ca²⁺ levels, followed by up regulation of nNOS, dysfunction of mitochondria, ROS production, ER stress, and release of lysosomal enzymes. Excessive calcium concentration is the key mediator of glutamate toxicity through over activation of ionotropic and metabotropic receptors. In addition, glutamate accumulation can also inhibit cystine (CySS) uptake by reversing the action of the CySS/glutamate antiporter. Reversal of the antiporter action reinforces the aforementioned events by depleting neurons of cysteine and eventually glutathione’s reducing potential. Various cell lines have been employed in the pursuit to understand the mechanism(s) by which excitotoxicity affects the cells leading them ultimately to their demise. In some cell lines glutamate toxicity is exerted mainly through over activation of NMDA, AMPA, or kainate receptors whereas in other cell lines lacking such receptors, the toxicity is due to glutamate induced oxidative stress. However, in the greatest majority of the cell lines ionotropic glutamate receptors are present, co-existing to CySS/glutamate antiporters and metabotropic glutamate receptors, supporting the assumption that excitotoxicity effect in these cells is accumulative. Different cell lines differ in their responses when exposed to glutamate. In this review article the responses of PC12, SH-SY5Y, HT-22, NT-2, OLCs, C6, primary rat cortical neurons, RGC-5, and SCN2.2 cell systems are systematically collected and analyzed.

Riluzole increases glutamate uptake by cultured C6 astroglial cells

Riluzole is a drug approved for the treatment of amyotrophic lateral sclerosis (ALS) and may be effective for the treatment of other neurodegenerative and neuropsychiatric disorders. Riluzole exerts diverse actions on the central nervous system, including altering glutamate release and uptake, and therefore act diminishing glutamate extracellular levels, but the underlying mechanism of these actions is still unknown. Here, we demonstrate that riluzole stimulated glutamate uptake and augmented the expression of the glutamate EAAC1 transporter in C6 astroglial cell cultures. The effect of riluzole on glutamate uptake was reduced to below controls when it was co-administered with inhibitors of protein kinase C (PKC; bisindolylmaleimide II), phosphatidylinositol 3-kinase (PI3K; wortmannin) and fibroblast growth factor receptor 1 (FGFR1; PD173074). Riluzole also decreased reactive oxygen species load with no effect on glutathione levels. This study investigates three independent intracellular pathways and the mechanism of action of riluzole on glutamate metabolism.

A pilot study of hippocampal volume and N-acetylaspartate (NAA) as response biomarkers in riluzole-treated patients with GAD

Anxiolytic benefit following chronic treatment with the glutamate modulating agent riluzole in patients with generalized anxiety disorder (GAD) was previously associated with differential changes in hippocampal NAA concentrations. Here, we investigated the association between hippocampal volume and hippocampal NAA in the context of riluzole response in GAD. Eighteen medication-free adult patients with GAD received 8-week of open-label riluzole. Ten healthy subjects served as a comparison group. Participants underwent magnetic resonance imaging and spectroscopy at baseline and at the end of Week 8. GAD patients who completed all interventions were classified as remitters (n=7) or non-remitters (n=6), based on final Hamilton Anxiety Rating Scale (HAM-A) scores ≤7. At baseline, GAD patients had a significant reduction in total hippocampal volume compared to healthy subjects (F(1,21)=6.55, p=0.02). This reduction was most pronounced in the remitters, compared to non-remitters and healthy subjects. Delta (final-baseline) hippocampal volume was positively correlated with delta NAA in GAD. This positive association was highly significant in the right hippocampus in GAD [r=0.81, p=0.002], with no significant association in healthy subjects [Fisher r-to-z p=0.017]. Across all GAD patients, delta hippocampal volume was positively associated with improvement in HAM-A (rspearman=0.62, p=0.03). These preliminary findings support hippocampal NAA and volume as neural biomarkers substantially associated with therapeutic response to a glutamatergic drug.

Neuroprotection for amyotrophic lateral sclerosis: role of stem cells, growth factors, and gene therapy

Various molecular mechanisms including apoptosis, inflammation, oxidative stress, mitochondrial dysfunction and excitotoxicity have been implicated in the pathogenesis of amyotrophic lateral sclerosis (ALS), though the exact mechanisms have yet to be specified. Furthermore, the underlying restorative molecular mechanisms resulting in neuronal and/or non-neuronal regeneration have to be yet elucidated. Therapeutic agents targeting one or more of these mechanisms to combat either initiation or progression of the disease are under research. Novel treatments including stem cell therapy, growth factors, and gene therapy might prolong survival and delay progression of symptoms. Harnessing the regenerative potential of the central nervous system would be a novel approach for the treatment of motor neuron death resulting from ALS. Endogenous neural replacement, if augmented with administration of exogenous growth factors or with pharmaceuticals that increase the rate of neural progenitor formation, neural migration, and neural maturation could slow the rate of cell loss enough to result in clinical improvement. In this review, we discuss the impact of therapeutic treatment involving stem cell therapy, growth factors, gene therapy, and combination therapy on disease onset and progression of ALS. In addition, we summarize human clinical trials of stem cell therapy, growth factor therapy, and gene therapy in individuals with ALS.

Oxidative stress in neurodegenerative diseases: mechanisms and therapeutic perspectives

The incidence and prevalence of neurodegenerative diseases (ND) increase with life expectancy. This paper reviews the role of oxidative stress (OS) in ND and pharmacological attempts to fight against reactive oxygen species (ROS)-induced neurodegeneration. Several mechanisms involved in ROS generation in neurodegeneration have been proposed. Recent articles about molecular pathways involved in ROS generation were reviewed. The progress in the development of neuroprotective therapies has been hampered because it is difficult to define targets for treatment and determine what should be considered as neuroprotective. Therefore, the attention was focused on researches about pharmacological targets that could protect neurons against OS. Since it is necessary to look for genes as the ultimate controllers of all biological processes, this paper also tried to identify gerontogenes involved in OS and neurodegeneration. Since neurons depend on glial cells to survive, recent articles about the functioning of these cells in aging and ND were also reviewed. Finally, clinical trials testing potential neuroprotective agents were critically reviewed. Although several potential drugs have been screened in in vitro and in vivo models of ND, these results were not translated in benefit of patients, and disappointing results were obtained in the majority of clinical trials.

Neurotoxic injury pathways in differentiated mouse motor neuron-neuroblastoma hybrid (NSC-34D) cells in vitro--limited effect of riluzole on thapsigargin, but not staurosporine, hydrogen peroxide and homocysteine neurotoxicity

The neuroblastoma-spinal motor neuron fusion cell line, NSC-34, in its differentiated form, NSC-34D, permits examining the effects of riluzole, a proven treatment for amyotrophic lateral sclerosis (ALS) on cell death induction by staurosporine (STS), thapsigargin (Thaps), hydrogen peroxide (H(2)O(2)) and homocysteine (HCy). These neurotoxins, applied exogenously, have mechanisms of action related to the various proposed molecular pathogenetic pathways in ALS and are differentiated from endogenous cell death that is associated with cytoplasmic aggregate formation in motor neurons. Nuclear morphology, caspase-3/7 activation and high content imaging were used to assess toxicity of these neurotoxins with and without co-treatment with riluzole, a benzothiazole compound with multiple pharmacological actions. STS was the most potent neurotoxin at killing NSC-34D cells with a toxic concentration at which 50% of maximal cell death is achieved (TC(50)=0.01μM), followed by Thaps (TC(50)=0.9μM) and H(2)O(2) (TC(50)=15μM) with HCy requiring higher concentrations to kill at the same level (TC(50)=2200μM). Riluzole provided neurorescue with a 20% absolute reduction (47.6% relative reduction) in apoptotic cell death against Thaps-induced NSC-34D cell (p≤0.05), but had no effect on STS-, H(2)O(2)- and HCy-induced NSC-34D cell death. This effect of riluzole on Thaps induction of cell death was independent of caspase-3/7 activation. Riluzole mitigated a toxin that can cause intracellular calcium dysregulation associated with endoplasmic reticulum (ER) stress but not toxins associated with other cell death mechanisms.

Riluzole elevates GLT-1 activity and levels in striatal astrocytes

Drugs which upregulate astrocyte glutamate transport may be useful neuroprotective compounds by preventing excitotoxicity. We set up a new system to identify potential neuroprotective drugs which act through GLT-1. Primary mouse striatal astrocytes grown in the presence of the growth-factor supplement G5 express high levels of the functional glutamate transporter, GLT-1 (also known as EAAT2) as assessed by Western blotting and ³H-glutamate uptake assay, and levels decline following growth factor withdrawal. The GLT-1 transcriptional enhancer dexamethasone (0.1 or 1 μM) was able to prevent loss of GLT-1 levels and activity following growth factor withdrawal. In contrast, ceftriaxone, a compound previously reported to enhance GLT-1 expression, failed to regulate GLT-1 in this system. The neuroprotective compound riluzole (100 μM) upregulated GLT-1 levels and activity, through a mechanism that was not dependent on blockade of voltage-sensitive ion channels, since zonasimide (1 mM) did not regulate GLT-1. Finally, CDP-choline (10 μM-1 mM), a compound which promotes association of GLT-1/EAAT2 with lipid rafts was unable to prevent GLT-1 loss under these conditions. This observation extends the known pharmacological actions of riluzole, and suggests that this compound may exert its neuroprotective effects through an astrocyte-dependent mechanism.

Delayed neuroprotection by riluzole against excitotoxic damage evoked by kainate on rat organotypic spinal cord cultures

Kainate-mediated excitotoxicity of organotypic spinal cord cultures is an in vitro model advantageous to investigate basic mechanisms of acute spinal injury and its pharmacological neuroprotection. Using such cultures, the putative neuroprotective agent riluzole applied at 5 μM (plasma therapeutic concentration) was studied for its ability to prevent neurotoxicity evoked by 1 h administration of kainate. We monitored real-time release of glutamate, release of lactate dehydrogenase (LDH) (cell damage marker), occurrence of cell pyknosis, the number of surviving neurons and motoneurons, and cell culture metabolic activity. Co-applied riluzole strongly blocked the kainate-evoked early rise in extracellular glutamate (via calcium dependent or independent processes) and suppressed LDH release (limited to <20% of total). Although there were no significant cell losses within the first h after kainate washout, pyknosis, fewer neurons and motoneurons were observed 24 h later. MTT assay demonstrated that surviving cells were metabolically competent. Co-application of kainate and tetrodotoxin also failed to protect spinal cord slices 24 h later. When riluzole application begun at kainate washout and continued for 24 h, significant neuroprotection was observed for neurons in the central and dorsal regions, while ventral horn cells (including motoneurons) were not protected. Our data suggest that riluzole neuroprotection against excitotoxicity was feasible, although it paradoxically required delayed drug administration, and was not extended to the ventral horn. We propose that riluzole was acting on yet-unidentified processes downstream of glutamate release and receptor activation. Deciphering their identity and role in cell death mechanisms may be an important goal to develop neuroprotection.