Docosahexaenoic acid induces ERK1/2 activation and neuritogenesis via intracellular reactive oxygen species production in human neuroblastoma SH-SY5Y cells

Epigenetic regulation exerted by Caliphruria subedentata and galantamine: an in vitro and in silico approach for mimic Alzheimer's disease

At the interface between genes and environment, epigenetic mechanisms, including DNA methylation and histone modification, regulate neurogenic processes such as differentiation, proliferation, and maturation of neural stem cells. However, these mechanisms are altered in Alzheimer's disease (AD), a neurodegenerative condition that mainly affects older adults. Since epigenetic mechanisms are known to be reversible, a number of molecules from natural sources are being studied as epigenetic regulators in AD. Recently, in vitro and in silico studies have shown that C. subedentata and its alkaloids modulated neurotoxicity. However, studies exploring the epigenetic activity of these alkaloids are limited. We conducted a set of bioassays to evaluate neuronal differentiation and the sensitivity of undifferentiated SH-SY5 cells against a neurotoxic stimulus. In addition, we analyzed the methylation profiles in genes such as APP, PSI, and BACE1 due to their role in amyloid processing. Docking and molecular dynamic analysis were used to explore the effect exerted by C. subedentata alkaloids on the regulation of histone deacetylases (HDAC2, HDAC3 and HDAC7). The results demonstrated that C. subedentata and galantamine induce neuronal differentiation and protect the undifferentiated SH-SY5Y cells against Aβ(1-42)-induced neurotoxicity. The methylation profiles of the studied genes show no statistically significant differences between C. subedentata, galantamine. However, these findings should be interpreted with caution, since small changes in methylation promoters in the brain could not be easily detected. Results from in silico approaches describe for the first time the potential promissing epigenetic effects of galantamine by regulating HDAC3 and HDAC7 modification.Communicated by Ramaswamy H. Sarma.

DHA Induces Cell Death through the Production of ROS and the Upregulation of CHOP in Fibroblast-like Synovial Cells from Human Rheumatoid Arthritis Patients

Rheumatoid arthritis (RA) is an inflammatory disease marked by a massive proliferation of synovial cells in the joints. In this study, we investigated the pro-apoptotic effects of docosahexaenoic acid (DHA) in human fibroblast-like synovial cells from RA patients (RA-FLS). An in vitro study using MH7A cells showed that DHA treatment induced caspase-8-dependent apoptosis in a dose-dependent manner and reduced the TNF-α-mediated induction of MMP-9 and IL-1β. DHA also induced the phosphorylation of eIF2α, the expression of the ER stress markers ATF4 and C/EBP homologous protein (CHOP), and death receptor 5 (DR5). The knockdown of CHOP or DR5 increased cell viability and reduced apoptosis in DHA-treated cells. Furthermore, the knockdown of CHOP reduced DHA-mediated DR5 expression, while the overexpression of CHOP increased DR5 expression. We also found that DHA treatment induced the accumulation of reactive oxygen species (ROS), and pretreatment with the anti-oxidant Tiron effectively abrogated not only the expression of CHOP and DR5, but also DHA-induced apoptosis. Under this condition, cell viability was increased, while PARP-1 cleavage and caspase-8 activation were reduced. All the findings were reproduced in human primary synovial cells obtained from RA patients. These results suggest that the DHA-mediated induction of ROS and CHOP induced apoptosis through the upregulation of DR5 in RA-FLSs, and that CHOP could be used as a therapy for RA.

Neuroprotective Effect of Stearidonic Acid on Amyloid β-Induced Neurotoxicity in Rat Hippocampal Cells

Dietary intake of omega-3 fatty acids found in fish has been reported to reduce the risk of Alzheimer's Disease (AD). Stearidonic acid (SDA), a plant-based omega-3 fatty acid, has been targeted as a potential surrogate for fish-based fatty acids. However, its role in neuronal degeneration is unknown. This study was designed to evaluate effects of SDA on Amyloid-β(A-β)-induced neurotoxicity in rat hippocampal cells. Results showed that SDA effectively converted to eicosapentaenoic acid (EPA) in hippocampal cells. Aβ-induced apoptosis in H19-7 cells was protected by SDA pretreatment as evidenced by its regulation on the expression of relevant pro- and anti-apoptotic genes, as well as the inhibition on caspase activation. SDA also protected H19-7 cells from Aβ-induced oxidative stress by regulating the expression of relevant pro- and anti-oxidative genes, as well as the improvement in activity of catalase. As for Aβ/LPS-induced neuronal inflammation, SDA pretreatment reduced the release of IL-1β and TNFα. Further, we found that the anti-Aβ effect of SDA involves its inhibition on the expression of amyloid precursor protein and the regulation on MAPK signaling. These results demonstrated that SDAs have neuroprotective effect in Aβ-induced H19-7 hippocampal cells. This beneficial effect of SDA was attributed to its antiapoptotic, antioxidant, and anti-inflammatory properties.

Luteolin stimulates the NGF-induced neurite outgrowth in cultured PC12 cells through binding with NGF and potentiating its receptor signaling

Luteolin, a flavonoid in fruits and vegetables, has neurotrophic functions without a well-characterized mechanism. Here, we hypothesize a direct interaction of luteolin with nerve growth factor (NGF); as such, the functionality of the NGF could be potentiated. The direct binding of luteolin with NGF was validated by ultra-filtration, Biacore, and docking analyses. In cultured PC12 cells, application of luteolin in combination with a low dose of NGF potentiated the NGF-induced differentiation of neurons by an increase of the differentiated cell number to 25.4 ± 4.8% (p < 0.01), as well as the increased expression of neurofilaments by 119 ± 32.1% (p < 0.05), 191 ± 12.6% (p < 0.01), and 110 ± 23.4% (p < 0.05) for NF68, NF160 and NF200, respectively. The co-treatment induced the phosphorylations of tropomyosin receptor kinase A (TrkA), extracellular signal-regulated kinase 1/2 (ERK1/2), protein kinase B (Akt), phospholipase C-γ1 (PLCγ1), and cAMP response element-binding protein (CREB) by 2 to 3 fold: these induced phosphorylations were mimicking that of a high dose of NGF. Moreover, the application of the TrkA inhibitor, K252a, blocked the luteolin-mediated induction of neurofilament expression and neurite outgrowth in cultured PC12 cells, suggesting the target specificity. The result supports the development of luteolin as a therapeutic, or preventive, agent for NGF insufficiency-associated neurodegenerative diseases.

N-3 PUFA-Deficiency in Early Life Exhibits Aggravated MPTP-Induced Neurotoxicity in Old Age while Supplementation with DHA/EPA-Enriched Phospholipids Exerts a Neuroprotective Effect

INTRODUCTION

Malnutrition in early life affects the growth and development of fetus and children, which has a long-term impact on adult health. Previous studies reveal a relationship between dietary omega-3 polyunsaturated fatty acid (n-3 PUFA) content, brain development, and the prevalence of neurodevelopmental disorders and inflammation. However, it is unclear about the effect of n-3 PUFA-deficiency in early life on the development of Parkinson's disease (PD) in old age, as well as the neuroprotective effect of DHA- and EPA-enriched phospholipids (DHA/EPA-PLs) supplemented in old age in long-term n-3 PUFA-deficient mice.

METHODS AND RESULTS

The PD mice induced by 1-methyl-4-phenyl-1,2,3,6- tetrahydropyridine (MPTP) in n-3 PUFA-adequate (N) and -deficient (DEF) group are supplemented with a DHA/EPA-PLs diet for 2 weeks (N+DPL, DEF+DPL). DHA/EPA-PLs supplementation significantly protects against MPTP-induced impairments. The DEF+DPL group shows poorer motor performance, the loss of dopaminergic neurons, mitochondrial dysfunction, and neurodevelopment delay than the N+DPL group, and still did not recover to the Control level.

CONCLUSIONS

Dietary n-3 PUFA-deficiency in early life exhibits more aggravated MPTP-induced neurotoxicity in old age, than DHA/EPA-PLs supplementation recovers brain DHA levels and exerts neuroprotective effects in old age in long-term n-3 PUFA-deficient mice, which might provide a potential dietary guidance.

An appropriate ratio of unsaturated fatty acids is the constituent of hickory nut extract for neurite outgrowth in human SH-SY5Y cells

Hickory nuts (Carya cathayensis Sarg, CCS), a well-known Chinese medicinal nut, is thought to improve memory in Chinese folks. However, functional constituents have not been scientifically identified. In this study, human SH-SY5Y cells, combined with Q-TOF mass spectrometry (Q-TOF-MS) and standard substances, were used to evaluate the function in neuronal development and to identify constituents of CCS hydrophobic extracts (CCS-HE). Data showed that CCS-HE but not the control induced neurite outgrowth of SH-SY5Y cells in a dose-dependent manner, supported by which CCS-HE induced the expression of nerve growth factor (NGF), neurofilament 160 (NF160), and neuronal peptide Y (NPY) mRNA. Q-TOF-MS analysis with standard substances indicated that linolenic acid (LNA), linoleic acid (LA), and oleic acid (OA) were the main constituents in CCS-HE. Furthermore, mixtures of these unsaturated fatty acids (UFAs) at the natural ratio (1:8:16) significantly induced neurite outgrowth and gene expression of NGF, NF160, and NPY in a dose-dependent manner. However, the individual and alternative ratios were not effective to induce the neurite outgrowth and gene expression of NGF, NF160, and NPY. These data implicate that an appropriate ratio of UFAs is the main constituent for the neurite outgrowth.

Direct evidence of bradycardic effect of omega-3 fatty acids acting on nucleus ambiguus

Docosahexaenoic acid (DHA) an omega-3 polyunsaturated fatty acid, is an agonist of FFA1 receptor. DHA administration reduces the heart rate via unclear mechanisms. We examined the effect of DHA on neurons of nucleus ambiguus that provide the parasympathetic control of heart rate. DHA produced a dose-dependent increase in cytosolic Ca²⁺ concentration in cardiac-projecting nucleus ambiguus neurons; the effect was prevented by GW1100, a FFA1 receptor antagonist. DHA depolarized cultured nucleus ambiguus neurons via FFA1 activation. Bilateral microinjection of DHA into nucleus ambiguus produced bradycardia in conscious rats. Our results indicate that DHA decreases heart rate by activation of FFA1 receptor on cardiac-projecting nucleus ambiguus neurons.

Docosahexaenoic Acid: Outlining the Therapeutic Nutrient Potential to Combat the Prenatal Alcohol-Induced Insults on Brain Development

Brain development is markedly affected by prenatal alcohol exposure, leading to cognitive and behavioral problems in the children. Protecting neuronal damage from prenatal alcohol could improve neural connections and functioning of the brain. DHA, a n-3 (ω-3) long-chain PUFA, is involved in the development of neurons. Insufficient concentrations of DHA impair neuronal development and plasticity of synaptic junctions and affect neurotransmitter concentrations in the brain. Alcohol consumption during pregnancy decreases the maternal DHA status and reduces the placental transfer of DHA to the fetus, resulting in less DHA being available for brain development. It is important to know whether DHA could induce beneficial effects on various physiological functions that promote neuronal development. This review will discuss the current evidence for the beneficial role of DHA in protecting against neuronal damage and its potential in mitigating the teratogenic effects of alcohol.

Isoliquiritigenin Attenuates Anxiety-Like Behavior and Locomotor Sensitization in Rats after Repeated Exposure to Nicotine

As important components of positive and negative reinforcement, locomotor sensitization and withdrawal anxiety following repeated exposure to nicotine (NIC) constitute crucial risk factors for relapse to NIC use after abstinence. Glycyrrhiza radix (G. radix), an important tonic used in traditional Oriental medicine, has not only anxiolytic effects but also reduces NIC-induced locomotor sensitization. Isoliquiritigenin (ISL), a bioactive ingredient of G. radix, also exhibits neuropharmacological effects, including anxiolytic action. Previously, we reported that ISL suppressed cocaine-induced extracellular dopamine release in the nucleus accumbens shell (NaccSh) and attenuated methamphetamine-induced neurotoxicity. The present study was performed to evaluate the effects of ISL on both NIC withdrawal anxiety and locomotor sensitization. Adult male rats received subcutaneous administration of NIC hydrogen tartrate (0.4 mg/kg, twice a day) for 7 days followed by 4 days of withdrawal. During the period of NIC withdrawal, the rats received four intragastric treatments with ISL (3, 10, or 30 mg/kg/day). All three doses of ISL significantly inhibited NIC withdrawal-induced anxiety-like behaviors in the elevated plus maze (EPM) test, but only the 10 mg/kg/day and 30 mg/kg/day ISL doses attenuated locomotor sensitization induced by a challenge dose of NIC. Intracerebroventricular ISL also inhibited both NIC-induced withdrawal anxiety and locomotor sensitization, but intra-NaccSh injection of ISL blocked only NIC locomotor sensitization, which was abolished by post-ISL infusion of tert-butyl hydroperoxide (an oxidant) or N-methyl-d-aspartate (NMDA) into the NaccSh. Moreover, there was increased protein expression of phosphorylated Erk1/2 in the NIC-sensitized NaccSh, which was suppressed by ISL. Taken together, these results suggest that ISL can inhibit repeated NIC-induced withdrawal anxiety and locomotor sensitization, and the latter is mediated by antagonizing accumbal reactive oxygen species and NMDA receptor signaling.

Modulation of mitochondrial respiration underpins neuronal differentiation enhanced by lutein

Lutein is a dietary carotenoid of particular nutritional interest as it is preferentially taken up by neural tissues. Often linked with beneficial effects on vision, a broader role for lutein in neuronal differentiation has emerged recently, although the underlying mechanisms for these effects are not yet clear. The purpose of this study was to investigate the effect of lutein on neuronal differentiation and explore the associated underpinning mechanisms. We found that lutein treatment enhanced the differentiation of SH-SY5Y cells, specifically increasing neuronal arborization and expression of the neuronal process filament protein microtubule-associated protein 2. This effect was mediated by the intracellular phosphoinositide-3-kinase (PI3K) signaling pathway. While PI3K activity is a known trigger of neuronal differentiation, more recently it has also been shown to modulate the metabolic state of cells. Our analysis of bioenergetics found that lutein treatment increased glucose consumption, rates of glycolysis and enhanced respiratory activity of mitochondrial complexes. Concomitantly, the generation of reactive oxygen species was increased (consistent with previous reports that reactive oxygen species promote neuronal differentiation), as well as the production of the key metabolic intermediate acetyl-CoA, an essential determinant of epigenetic status in the cell. We suggest that lutein-stimulated neuronal differentiation is mediated by PI3K-dependent modulation of mitochondrial respiration and signaling, and that the consequential metabolic shifts initiate epigenetically dependent transcriptomic reprogramming in support of this morphogenesis. These observations support the potential importance of micronutrients supplementation to neurogenesis, both during normal development and in regenerative repair.

Status of topoisomerase-2β protein in all-trans retinoic acid-treated human neuroblastoma (SK-N-SH) cells

Of the mammalian topoisomerase (Topo)-2 isozymes (α and β), Topo-2β protein has been reported to regulate neuronal development and differentiation. However, the status of Topo-2β in all-trans retinoic acid (ATRA)-treated human neuroblastoma (SK-N-SH) cells is not understood. More information about the effects of ATRA on SK-N-SH cells is needed to reveal the role of ATRA in the regulation of Topo-2β levels and spontaneous regression of SK-N-SH cells to predict the clinical activity. This study was proposed to investigate the status and role of Topo-2β protein in ATRA-induced survival and neuronal differentiation of SK-N-SH cells. Microscopic, sodium dodecyl sulfate polyacrylamide gel electrophoresis after immunoprecipitations and Western blot analysis were used to study and compare Topo-2β protein among 10 µM ATRA-treated SK-N-SH cells and controls at different time points. The level of Topo-2β protein increased in the initial days of treatment but markedly decreased upon induction of differentiation by ATRA in later stages. Upon ATRA treatment, SK-N-SH cells stretched, exhibited neurite extensions, and acquired a neuronal phenotype. Both treated and untreated SK-N-SH cells were able to migrate, occupy the scratched area, and completely recolonized 24 hours later. These results suggest an indirect role of Topo-2β protein in regulation of genes involved in cell migration and differentiation of ATRA-treated SK-N-SH cells. This study suggests that Topo-2β may be part of activation/repression of protein complexes activated by epigenetic modifying agents, differentiating signals, and inducible locus. However, detailed studies are needed to explore the ATRA-downstream genes leading to Topo-2β regulation and regulatory proteins of neuronal differentiation.

Redox Signaling Mechanisms in Nervous System Development

SIGNIFICANCE

Numerous studies have demonstrated the actions of reactive oxygen species (ROS) as regulators of several physiological processes. In this study, we discuss how redox signaling mechanisms operate to control different processes such as neuronal differentiation, oligodendrocyte differentiation, dendritic growth, and axonal growth. Recent Advances: Redox homeostasis regulates the physiology of neural stem cells (NSCs). Notably, the neuronal differentiation process of NSCs is determined by a change toward oxidative metabolism, increased levels of mitochondrial ROS, increased activity of NADPH oxidase (NOX) enzymes, decreased levels of Nrf2, and differential regulation of different redoxins. Furthermore, during the neuronal maturation processes, NOX and MICAL produce ROS to regulate cytoskeletal dynamics, which control the dendritic and axonal growth, as well as the axonal guidance.

CRITICAL ISSUES

The redox homeostasis changes are, in part, attributed to cell metabolism and compartmentalized production of ROS, which is regulated, sensed, and transduced by different molecules such as thioredoxins, glutaredoxins, peroxiredoxins, and nucleoredoxin to control different signaling pathways in different subcellular regions. The study of how these elements cooperatively act is essential for the understanding of nervous system development, as well as the application of regenerative therapies that recapitulate these processes.

FUTURE DIRECTIONS

The information about these topics in the last two decades leads us to the conclusion that the role of ROS signaling in development of the nervous system is more important than it was previously believed and makes clear the importance of exploring in more detail the mechanisms of redox signaling. Antioxid. Redox Signal. 28, 1603-1625.

Self-assembling soft structures for intracellular NO release and promotion of neurite outgrowth

Nitric oxide (NO), an endogenously produced free radical species, is an extremely important signalling molecule in several biochemical processes related to neurotransmission, neuronal communication, and vasodilation, to name a few. Other than relying on endogenous synthesis, intracellular NO delivery presents an interesting challenge to fully exploit the therapeutic potential of this gaseous molecule. We have applied a self-assembling peptide conjugate strategy to devise a construct carrying a NO-release arm, which can be activated under standard redox conditions. Consequently, a tryptophan-based peptide carrier was designed, which self-assembled in the solution phase to afford soft nanospherical structures, and released NO in Neuro2a cell line, resulting in neurite outgrowth.

α-Tocopherol at Nanomolar Concentration Protects Cortical Neurons against Oxidative Stress

The aim of the present work is to study the mechanism of the α-tocopherol (α-T) protective action at nanomolar and micromolar concentrations against H₂O₂-induced brain cortical neuron death. The mechanism of α-T action on neurons at its nanomolar concentrations characteristic for brain extracellular space has not been practically studied yet. Preincubation with nanomolar and micromolar α-T for 18 h was found to increase the viability of cortical neurons exposed to H₂O₂; α-T effect was concentration-dependent in the nanomolar range. However, preincubation with nanomolar α-T for 30 min was not effective. Nanomolar and micromolar α-T decreased the reactive oxygen species accumulation induced in cortical neurons by the prooxidant. Using immunoblotting it was shown that preincubation with α-T at nanomolar and micromolar concentrations for 18 h prevented Akt inactivation and decreased PKCδ activation induced in cortical neurons by H₂O₂. α-T prevented the ERK1/2 sustained activation during 24 h caused by H₂O₂. α-T at nanomolar and micromolar concentrations prevented a great increase of the proapoptotic to antiapoptotic proteins (Bax/Bcl-2) ratio, elicited by neuron exposure to H₂O₂. The similar neuron protection mechanism by nanomolar and micromolar α-T suggests that a “more is better” approach to patients’ supplementation with vitamin E or α-T is not reasonable.

Anti-inflammatory effects of docosahexaenoic acid: Implications for its cancer chemopreventive potential

The implication of inflammatory tissue damage in pathophysiology of human cancer as well as some metabolic disorders has been under intense investigation. Numerous studies have identified a series of critical signaling molecules involved in cellular responses to inflammatory stimuli. These include nuclear factor κB, peroxisome proliferator-activated receptor γ, nuclear factor erythroid 2 p45-related factor 2 and sterol regulatory element-binding protein 1. The proper regulation of these transcription factors mediating pro- and anti-inflammatory signaling hence provides an important strategy for the chemoprevention of inflammation-associated cancer. There is compelling evidence supporting that dietary supplementation with fish oil-derived ω-3 polyunsaturated fatty acids including docosahexaenoic acid (DHA) ameliorates symptomatic inflammation associated with cancer as well as other divergent human disorders. Acute or physiologic inflammation is an essential body's first line of defence to microbial infection and tissue injuries, but it must be properly completed by a process termed 'resolution'. Failure of resolution mechanisms can result in persistence of inflammation, leading to chronic inflammatory conditions and related malignancies. The phagocytic engulfment of apoptotic neutrophils and clearance of their potentially histotoxic contents by macrophages, called efferocytosis is an essential component in resolving inflammation. Of note, DHA is a precursor of endogenous proresolving lipid mediators which regulate the leukocyte trafficking and recruitment and thereby facilitate efferocytosis. Therefore, DHA and its metabolites may have a preventive potential in the management of human cancer which arises as a consequence of impaired resolution of inflammation as well as chronic inflammation.

Dimethylsulfoniopropionate Promotes Process Outgrowth in Neural Cells and Exerts Protective Effects against Tropodithietic Acid

The marine environment harbors a plethora of bioactive substances, including drug candidates of potential value in the field of neuroscience. The present study was undertaken to investigate the effects of dimethylsulfoniopropionate (DMSP), produced by several algae, corals and higher plants, on cells of the mammalian nervous system, i.e., neuronal N2a and OLN-93 cells as model system for nerve cells and glia, respectively. Additionally, the protective capabilities of DMSP were assessed in cells treated with tropodithietic acid (TDA), a marine metabolite produced by several Roseobacter clade bacteria. Both cell lines, N2a and OLN-93, have previously been shown to be a sensitive target for the action of TDA, and cytotoxic effects of TDA have been connected to the induction of oxidative stress. Our data shows that DMSP promotes process outgrowth and microtubule reorganization and bundling, accompanied by an increase in alpha-tubulin acetylation. Furthermore, DMSP was able to prevent the cytotoxic effects exerted by TDA, including the breakdown of the mitochondrial membrane potential, upregulation of heat shock protein Hsp32 and activation of the extracellular signal-regulated kinases 1/2 (ERK1/2). Our study points to the conclusion that DMSP provides an antioxidant defense, not only in algae but also in mammalian neural cells.

Uridine from Pleurotus giganteus and Its Neurite Outgrowth Stimulatory Effects with Underlying Mechanism

Neurodegenerative diseases are linked to neuronal cell death and impairment of neurite outgrowth. An edible mushroom, Pleurotus giganteus was found to stimulate neurite outgrowth in vitro but the chemical constituents and the underlying mechanism is yet to be elucidated. The chemical constituents of P. giganteus (linoleic acid, oleic acid, cinnamic acid, caffeic acid, p-coumaric acid, succinic acid, benzoic acid, and uridine) were tested for neurite outgrowth activity. Uridine (100 μM) was found to increase the percentage of neurite-bearing cells of differentiating neuroblastoma (N2a) cells by 43.1±0.5%, which was 1.8-fold higher than NGF (50 ng/mL)-treated cells. Uridine which was present in P. giganteus (1.80±0.03 g/100g mushroom extract) increased the phosphorylation of extracellular-signal regulated kinases (ERKs) and protein kinase B (Akt). Further, phosphorylation of the mammalian target of rapamycin (mTOR) was also increased. MEK/ERK and PI3K-Akt-mTOR further induced phosphorylation of cAMP-response element binding protein (CREB) and expression of growth associated protein 43 (GAP43); all of which promoted neurite outgrowth of N2a cells. This study demonstrated that P. giganteus may enhance neurite outgrowth and one of the key bioactive molecules responsible for neurite outgrowth is uridine.

Neurite outgrowth stimulation by n-3 and n-6 PUFAs of phospholipids in apoE-containing lipoproteins secreted from glial cells

PUFAs, which account for 25-30% of the total fatty acids in the human brain, are important for normal brain development and cognitive function. However, it remains unclear how PUFAs are delivered to neurons and exert their effects. In this study, we demonstrated that n-3 and n-6 PUFAs added to the medium are incorporated into membrane phospholipids of primary glial cells from rat cortices, and then secreted as the fatty acid moiety of phospholipids in apoE-containing lipoproteins (LpEs). Tandem mass spectrometry analysis further showed that LpEs secreted from glial cells contain a variety of metabolites of PUFAs produced in glial cells by elongation and unsaturation. LpEs are absorbed by endocytosis into neurons via LDL receptor-related protein 1. LpE-containing n-3 and n-6 PUFAs exhibit a strong effect on neurite outgrowth of hippocampal neurons by increasing the number of branches. This study sheds light on the novel role of LpEs in the central nervous system and also a novel pathway in which PUFAs act on neurons.

Light, lipids and photoreceptor survival: live or let die?

Due to its constant exposure to light and its high oxygen consumption the retina is highly sensitive to oxidative damage, which is a common factor in inducing the death of photoreceptors after light damage or in inherited retinal degenerations. The high content of docosahexaenoic acid (DHA), the major polyunsaturated fatty acid in the retina, has been suggested to contribute to this sensitivity. DHA is crucial for developing and preserving normal visual function. However, further roles of DHA in the retina are still controversial. Current data support that it can tilt the scale either towards degeneration or survival of retinal cells. DHA peroxidation products can be deleterious to the retina and might lead to retinal degeneration. However, DHA has also been shown to act as, or to be the source of, a survival molecule that protects photoreceptors and retinal pigment epithelium cells from oxidative damage. We have established that DHA protects photoreceptors from oxidative stress-induced apoptosis and promotes their differentiation in vitro. DHA activates the retinoid X receptor (RXR) and the ERK/MAPK pathway, thus regulating the expression of anti and pro-apoptotic proteins. It also orchestrates a diversity of signaling pathways, modulating enzymatic pathways that control the sphingolipid metabolism and activate antioxidant defense mechanisms to promote photoreceptor survival and development. A deeper comprehension of DHA signaling pathways and context-dependent behavior is required to understand its dual functions in retinal physiology.

Resveratrol protects vascular smooth muscle cells against high glucose-induced oxidative stress and cell proliferation in vitro

Background

Resveratrol exhibits beneficial effects against numerous degenerative diseases at different stages of pathogenesis. This study investigated potential mechanisms and resveratrol effects on high glucose (HG)-induced oxidative stress (30 mM d-glucose, 30 min) and cell proliferation (30 mM d-glucose, 24 h) in vascular smooth muscle cells (VSMCs).

Material/Methods

Intracellular reactive oxygen species (ROS) generation was detected by 2′,7′-dichlorofluorescein diacetate (DCFH-DA). Total antioxidant capacity (TAC), malonyldialdehyde (MDA), glutathione (GSH), and superoxide dismutase (SOD) were measured to evaluate oxidative stress. VSMC proliferation was measured by CCK-8 assays and through propidium iodide-based cell cycle analysis. Expression of NAD(P)H oxidase, proliferation proteins, and cell signalling were assessed by immunoblot analysis.

Results

Co-treatment of primary cultures of VSMCs with 1–100 μM resveratrol decreased HG-induced ROS overproduction (P<0.05). Resveratrol also abolished HG-induced phosphorylation of oxidase subunit p47 phox and reduced HG-induced cyclin D1, cyclin E, and PCNA expression in a concentration-dependent manner. Furthermore, resveratrol (10 μM) attenuated HG-induced phosphorylation of Akt, p38 mitogen-activated protein kinase (MAPK), ERK 1/2, and JNK1/2 without affecting total levels. HG stimulation enhanced downstream IκB-α phosphorylation and NF-κB activity, and resveratrol repressed these effects.

Conclusions

Resveratrol inhibits HG-induced oxidative stress and VSMC proliferation by suppressing ROS generation, NADPH oxidase, Akt phosphorylation, p38 MAPK/JNK/ERK phosphorylation, and IκB-α and NF-κB activities.

Effects of docosahexaenoic Acid on neurotransmission

Docosahexaenoic acid (DHA) is the major polyunsaturated fatty acid (PUFA) in the brain and a structural component of neuronal membranes. Changes in DHA content of neuronal membranes lead to functional changes in the activity of receptors and other proteins which might be associated with synaptic function. Accumulating evidence suggests the beneficial effects of dietary DHA supplementation on neurotransmission. This article reviews the beneficial effects of DHA on the brain; uptake, incorporation and release of DHA at synapses, effects of DHA on synapses, effects of DHA on neurotransmitters, DHA metabolites, and changes in DHA with age. Further studies to better understand the metabolome of DHA could result in more effective use of this molecule for treatment of neurodegenerative or neuropsychiatric diseases.

Dexamethasone inhibits the maturation of newly formed neurons and glia supplemented with polyunsaturated fatty acids

Stress bears a negative impact on adult neurogenesis. High levels of corticoids have been shown to inhibit neural stem cell proliferation, and are considered responsible for the loss of neural precursors. Their effects on the differentiation of the glial and neuronal lineages have been less studied. We examined the effect of dexamethasone (Dex), a synthetic glucocorticoid, on the differentiation of rat neural stem cells in vitro. Dex had no effect on the differentiation of cells cultured under standard conditions. Since we previously determined that NSC, when cultured under classical conditions, were deprived of polyunsaturated fatty acids (PUFA), and displayed phospholipid compositions very different from the in vivo figures [1], we examined the effect of Dex under PUFA supplementation. Dex impaired neuron and oligodendrocyte maturation in PUFA-supplemented cells, demonstrated by the reduction of neurite lengths and oligodendrocyte sizes. This effect was mediated by the glucocorticoid receptor (GR), since it was eliminated by mifepristone, a GR antagonist, and could be relayed by a reduction of ERK phosphorylation. We determined that GR was associated with PPAR β and α under basal conditions, and that this association was disrupted when PUFA were added in combination with Dex. We assumed that this effect on the receptor status enabled the effect of Dex on PUFA supplemented cells, since we determined that the binding to the glucocorticoid response element was higher in cells incubated with PUFA and Dex. In conclusion, corticoids can impair NSC differentiation, and consequently impact the entire process of neurogenesis.

Activation of Rac1-dependent redox signaling is critically involved in staurosporine-induced neurite outgrowth in PC12 cells

Staurosporine, a non-specific protein kinase inhibitor, has been shown to induce neurite outgrowth in PC12 cells, but the mechanism by which staurosporine induces neurite outgrowth is still obscure. In the present study, we investigated whether the activation of Rac1 was responsible for the neurite outgrowth triggered by staurosporine. Staurosporine caused rapid neurite outgrowth independent of the ERK signaling pathways. In contrast, neurite outgrowth in response to staurosporine was accompanied by activation of Rac1, and the Rac1 inhibitor NSC23766 attenuated the staurosporine-induced neurite outgrowth in a concentration-dependent manner. In addition, suppression of Rac1 activity by expression of the dominant negative mutant Rac1N17 also blocked the staurosporine-induced morphological differentiation of PC12 cells. Staurosporine caused an activation of NADPH oxidase and increased the production of reactive oxygen species (ROS), which was prevented by NSC23766 and diphenyleneiodonium (DPI), an NADPH oxidase inhibitor. Staurosporine-induced neurite outgrowth was attenuated by pretreatment with DPI and exogenous addition of sublethal concentration of H2O2 accelerated neurite outgrowth triggered by staurosporine. These results indicate that activation of Rac1, which leads to ROS generation, is required for neurite outgrowth induced by staurosporine in PC12 cells.

Moderate superoxide production is an early promoter of mitochondrial biogenesis in differentiating N2a neuroblastoma cells

Reactive oxygen species (ROS) have been widely considered as harmful for cell development and as promoters of cell aging by increasing oxidative stress. However, ROS have an important role in cell signaling and they have been demonstrated to be beneficial by triggering hormetic signals, which could protect the organism from later insults. In the present study, N2a murine neuroblastoma cells were used as a paradigm of cell-specific (neural) differentiation partly mediated by ROS. Differentiation was triggered by the established treatments of serum starvation, forskolin or dibutyryl cyclic AMP. A marked differentiation, expressed as the development of neurites, was detected by fixation and staining with coomassie brilliant blue after 48 h treatment. This was accompanied by an increase in mitochondrial mass detected by mitotracker green staining, an increased expression of the peroxisome proliferator-activated receptor gamma (PPARγ) coactivator 1-alpha (PGC-1α) and succinate dehydrogenase activity as detected by MTT. In line with these results, an increase in free radicals, specifically superoxide anion, was detected in differentiating cells by flow cytometry. Superoxide scavenging by MnTBAP and MAPK inhibition by PD98059 partially reversed differentiation and mitochondrial biogenesis. In this way, we demonstrated that mitochondrial biogenesis and differentiation are mediated by superoxide and MAPK cues. Our data suggest that differentiation and mitochondrial biogenesis in N2a cells are part of a hormetic response which is triggered by a modest increase of superoxide anion concentration within the mitochondria.

Mulberry leaf extract inhibits cancer cell stemness in neuroblastoma

Emerging evidence proposes that most cancers originate from a rare subpopulation of cells, called cancer stem cells (CSCs), which possess characteristics including differentiation, self-renewal, and tumorigenicity. Currently, available therapeutic agents cannot effectively eliminate CSCs. Therefore, the development of a nontoxic, natural treatment that can either overcome chemoresistance or promote the elimination of CSCs is highly desirable. The current study examined whether mulberry leaf (ML) ethanolic extract can effectively eliminate neuroblastoma stem cell-like population. Our data demonstrated that 10-40 μg/ml of ML extract significantly enhanced differentiation by elongating neurites and reducing clonogenicity and sphere formation as shown by the decreased expression of stem cell markers and increased expression of differentiation markers. The knock-down of delta-like 1 homologue by siRNA enhanced the significant inhibitory effects of 40 μg/ml of ML extract on colony formation. Furthermore, phosphorylation of the extracellular signal-regulated kinase (ERK) was increased by 20 or 40 μg/ml of ML extract and the MEK/ERK inhibitors completely blocked differentiation induced by the extract. Taken together, these findings provide experimental evidence that ML may have chemopreventive effects on neuroblastoma cells by inhibiting CSCs characteristics as well as regulating CSCs pathways, which may provide a therapeutic option for controlling the growth of neuroblastoma cells.

Pleurotus giganteus (Berk.) Karunarathna & K.D. Hyde: Nutritional value and in vitro neurite outgrowth activity in rat pheochromocytoma cells

BACKGROUND

Drugs dedicated to alleviate neurodegenerative diseases like Parkinson's and Alzheimer's have always been associated with debilitating side effects. Medicinal mushrooms which harness neuropharmacological compounds offer a potential possibility for protection against such diseases. Pleurotus giganteus (formerly known as Panus giganteus) has been consumed by the indigenous people in Peninsular Malaysia for many years. Domestication of this wild mushroom is gaining popularity but to our knowledge, medicinal properties reported for this culinary mushroom are minimal.

METHODS

The fruiting bodies P. giganteus were analysed for its nutritional values. Cytotoxicity of the mushroom's aqueous and ethanolic extracts towards PC12, a rat pheochromocytoma cell line was assessed by using 3-[4,5-dimethythiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) assay. Neurite outgrowth stimulation assay was carried out with nerve growth factor (NGF) as control. To elucidate signaling mechanisms involved by mushroom extract-induced neurite outgrowth, treatment of specific inhibitor for MEK/ERK and PI3K signalling pathway was carried out.

RESULTS

The fruiting bodies of P. giganteus were found to have high carbohydrate, dietary fibre, potassium, phenolic compounds and triterpenoids. Both aqueous and ethanolic extracts induced neurite outgrowth of PC12 cells in a dose- and time-dependant manner with no detectable cytotoxic effect. At day 3, 25 μg/ml of aqueous extract and 15 μg/ml of ethanolic extract showed the highest percentage of neurite-bearing cells, i.e. 31.7 ± 1.1% and 33.3 ± 0.9%; respectively. Inhibition treatment results suggested that MEK/ERK and PI3K/Akt are responsible for neurite outgrowth of PC12 cells stimulated by P. giganteus extract. The high potassium content (1345.7 mg/100 g) may be responsible for promoting neurite extension, too.

CONCLUSIONS

P. giganteus contains bioactive compounds that mimic NGF and are responsible for neurite stimulation. Hence, this mushroom may be developed as a nutraceutical for the mitigation of neurodegenerative diseases.

Mitochondrial localized STAT3 is involved in NGF induced neurite outgrowth

Background

Signal transducer and activator of transcription 3 (STAT3) plays critical roles in neural development and is increasingly recognized as a major mediator of injury response in the nervous system. Cytokines and growth factors are known to phosphorylate STAT3 at tyrosine⁷⁰⁵ with or without the concomitant phosphorylation at serine⁷²⁷, resulting in the nuclear localization of STAT3 and subsequent transcriptional activation of genes. Recent evidence suggests that STAT3 may control cell function via alternative mechanisms independent of its transcriptional activity. Currently, the involvement of STAT3 mono-phosphorylated at residue serine⁷²⁷ (P-Ser-STAT3) in neurite outgrowth and the underlying mechanism is largely unknown.

Principal Findings

In this study, we investigated the role of nerve growth factor (NGF) induced P-Ser-STAT3 in mediating neurite outgrowth. NGF induced the phosphorylation of residue serine⁷²⁷ but not tyrosine⁷⁰⁵ of STAT3 in PC12 and primary cortical neuronal cells. In PC12 cells, serine but not tyrosine dominant negative mutant of STAT3 was found to impair NGF induced neurite outgrowth. Unexpectedly, NGF induced P-Ser-STAT3 was localized to the mitochondria but not in the nucleus. Mitochondrial STAT3 was further found to be intimately involved in NGF induced neurite outgrowth and the production of reactive oxygen species (ROS).

Conclusion

Taken together, the findings herein demonstrated a hitherto unrecognized novel transcription independent mechanism whereby the mitochondria localized P-Ser-STAT3 is involved in NGF induced neurite outgrowth.

Spatial phosphoprotein profiling reveals a compartmentalized extracellular signal-regulated kinase switch governing neurite growth and retraction

Brain development and spinal cord regeneration require neurite sprouting and growth cone navigation in response to extension and collapsing factors present in the extracellular environment. These external guidance cues control neurite growth cone extension and retraction processes through intracellular protein phosphorylation of numerous cytoskeletal, adhesion, and polarity complex signaling proteins. However, the complex kinase/substrate signaling networks that mediate neuritogenesis have not been investigated. Here, we compare the neurite phosphoproteome under growth and retraction conditions using neurite purification methodology combined with mass spectrometry. More than 4000 non-redundant phosphorylation sites from 1883 proteins have been annotated and mapped to signaling pathways that control kinase/phosphatase networks, cytoskeleton remodeling, and axon/dendrite specification. Comprehensive informatics and functional studies revealed a compartmentalized ERK activation/deactivation cytoskeletal switch that governs neurite growth and retraction, respectively. Our findings provide the first system-wide analysis of the phosphoprotein signaling networks that enable neurite growth and retraction and reveal an important molecular switch that governs neuritogenesis.

MEK/ERKs signaling is essential for lithium-induced neurite outgrowth in N2a cells

Lithium, a drug used for the treatment of bipolar disorder, has been shown to affect different aspects of neuronal development such as neuritogenesis, neurogenesis and survival. The underlying mechanism responsible for lithium's influence on neuronal development, however, still remains to be elucidated. In the present study, we demonstrate that lithium increases the phosphorylation of extracellular-signal regulated kinases (ERKs) and protein kinase B (Akt) and promotes neurite outgrowth in mouse N2a neuroblastoma cells (N2a). The inactivation of mitogen-activated protein kinase kinase (MEK)/ERKs signaling with a MEK inhibitor inhibits neurite outgrowth, but it enhances Akt activation in lithium-treated N2a cells. Furthermore, the inactivation of phosphoinositide-3-kinase (PI3K)/Akt signaling with a PI3K inhibitor increases both lithium-induced ERKs activation and lithium-induced neurite outgrowth. Taken together, our study suggests that lithium-induced neurite outgrowth in N2a cells is regulated by cross-talk between the MEK/ERKs and PI3K/Akt pathways and requires the activation of the MEK/ERKs signaling.

Mechanisms of n-3 fatty acid-mediated development and maintenance of learning memory performance

Docosahexaenoic acid (DHA, 22:6n-3) is specifically enriched in the brain and mainly anchored in the neuronal membrane, where it is involved in the maintenance of normal neurological function. Most DHA accumulation in the brain takes place during brain development in the perinatal period. However, hippocampal DHA levels decrease with age and in the brain disorder Alzheimer's disease (AD), and this decrease is associated with reduced hippocampal-dependent spatial learning memory ability. A potential mechanism is proposed by which the n-3 fatty acids DHA and eicosapentaenoic acid (20:5n-3) aid the development and maintenance of spatial learning memory performance. The developing brain or hippocampal neurons can synthesize and take up DHA and incorporate it into membrane phospholipids, especially phosphatidylethanolamine, resulting in enhanced neurite outgrowth, synaptogenesis and neurogenesis. Exposure to n-3 fatty acids enhances synaptic plasticity by increasing long-term potentiation and synaptic protein expression to increase the dendritic spine density, number of c-Fos-positive neurons and neurogenesis in the hippocampus for learning memory processing. In aged rats, n-3 fatty acid supplementation reverses age-related changes and maintains learning memory performance. n-3 fatty acids have anti-oxidative stress, anti-inflammation, and anti-apoptosis effects, leading to neuron protection in the aged, damaged, and AD brain. Retinoid signaling may be involved in the effects of DHA on learning memory performance. Estrogen has similar effects to n-3 fatty acids on hippocampal function. It would be interesting to know if there is any interaction between DHA and estrogen so as to provide a better strategy for the development and maintenance of learning memory.

Angiotensin II Inhibits Neuronal Nitric Oxide Synthase Activation Through the ERK1/2-RSK Signaling Pathway to Modulate Central Control of Blood Pressure

Rationale : Angiotensin (Ang) II exerts diverse physiological actions in both the peripheral and central neural systems. It was reported that the activity of Ang II is higher in the nucleus tractus solitarii (NTS) of spontaneously hypertensive rats (SHRs) and that angiotensin type-1 receptors are colocalized with NAD(P)H oxidase in the neurons of the NTS, resulting in the induction of local reactive oxygen species production by Ang II. However, the signaling mechanisms of Ang II that induce hypertension remain unclear.

Objective : The aim of this study was to investigate the possible signaling pathways involved in Ang II–mediated blood pressure regulation in the NTS.

Methods and Results : Male SHRs were treated with losartan or tempol for 2 weeks, after which systolic blood pressure was observed to decrease significantly. Dihydroethidium staining showed many cells with high reactive oxygen species in the NTS of SHRs. The addition of losartan or tempol decreased the numbers of reactive oxygen species–positive cells in the NTS. The systemic administration of losartan or tempol reduced the systolic blood pressure and increased NO production. Immunoblotting and immunohistochemical analysis further showed that inhibition of Ang II activity by losartan or tempol significantly increased the expression extracellular signal-regulated kinase (ERK)1/2, ribosomal protein S6 kinase (RSK), and also increased neuronal NO synthase (nNOS) phosphorylation. RSK was also found to bind directly to nNOS and induce phosphorylation at the Ser1416 position.

Conclusions : Taken together, these results suggest that the ERK1/2-RSK-nNOS signaling pathway may play a significant role in Ang II–mediated central blood pressure regulation.

Insulin receptor signaling regulates actin cytoskeletal organization in developing photoreceptors

The insulin receptor (IR) and IR signaling proteins are widely distributed throughout the CNS. IR signaling provides a trophic signal for transformed retinal neurons in culture and we recently reported that deletion of IR in rod photoreceptors by Cre/lox system resulted in stress-induced photoreceptor degeneration. These studies suggest a neuroprotective role of IR in rod photoreceptor cell function. However, there are no studies available on the role of insulin-induced IR signaling in the development of normal photoreceptors. To examine the role of insulin-induced IR signaling, we analyzed cultured neuronal cells isolated from newborn rodent retinas. In insulin-lacking cultures, photoreceptors from wild-type rat retinas exhibited an abnormal morphology with a wide axon cone and disorganization of the actin and tubulin cytoskeleton. Photoreceptors from IR knockout mouse retinas also exhibited a similar abnormal morphology. A novel finding in this study was that addition of docosahexaenoic acid, a photoreceptor trophic factor, restored normal axonal outgrowth in insulin-lacking cultures. These data suggest that IR signaling pathways regulate actin and tubulin cytoskeletal organization in photoreceptors; they also imply that insulin and docosahexaenoic acid activate at least partially overlapping signaling pathways that are essential for the development of normal photoreceptors.