3-Thiomethyl-5,6-(dimethoxyphenyl)-1,2,4-triazine improves neurite outgrowth and modulates MAPK phosphorylation and HSPs expression in H2O2-exposed PC12 cells

Preparation of recombinant neuritin protein

Neuritin plays an important role in promoting nerve injury repair and maintaining synaptic plasticity, making it a potential therapeutic target for the treatment of nerve injury and neurodegenerative diseases. The present study aimed to obtain an active, unlabeled neuritin protein. Initially, a neuritin protein expression system with an enterokinase site was constructed in Escherichia coli. After optimizing induction conditions and screening for high expression, a neuritin recombinant protein with purity exceeding 85 % was obtained through Ni-affinity chromatography. Subsequently, unlabeled neuritin with a molecular weight of 11 kDa was obtained through the enzymatic cleavage of the His label using an enterokinase. Furthermore, a neuritin recombinant protein with purity exceeding 95 % was obtained using gel chromatography. Functional investigations revealed that neurite outgrowth of PC12 cells was stimulated by the isolated neuritin. This study establishes a method to obtain active and unlabeled neuritin protein, providing a foundation for subsequent research on its biological functions.

Fusion with CTP increases the stability of recombinant neuritin

Neuritin is a vital neurotrophin that plays an essential role in recovery from nerve injury and neurodegenerative diseases and may become a new target for treating these conditions. However, improving neuritin protein stability is an urgent problem. In this study, to obtain active and stable neuritin proteins, we added a carboxyl-terminal peptide (CTP) sequence containing four O-linked glycosylation sites to the C-terminus of neuritin and cloned it into the Chinese hamster ovary (CHO) expression system. The neuritin-CTP protein was purified using a His-Tag purification strategy after G418 screening of stable high-expression cell lines. Ultimately, we obtained neuritin-CTP protein with a purity >90%. Functional analyses showed that the purified neuritin-CTP protein promoted the neurite outgrowth of PC12 cells, and stability experiments showed that neuritin stability was increased by adding CTP. These results indicate that neuritin protein-CTP fusion effectively increases stability without affecting secretion and activity. This study offers a sound strategy for improving the stability of neuritin protein and provides material conditions for further study of the function of neuritin.

A mimetic peptide of α2,6-sialyllactose promotes neuritogenesis

Oxidative stress contributes to the pathogenesis of neurodegenerative diseases. With the aim to find reagents that reduce oxidative stress, a phage display library was screened for peptides mimicking α2,6-sialyllactose (6'-SL), which is known to beneficially influence neural functions. Using Sambucus nigra lectin, which specifically binds to 6'-SL, we screened a phage display library and found a peptide comprising identical sequences of 12 amino acids. Mimetic peptide, reverse peptide and scrambled peptide were tested for inhibition of 6'-SL binding to the lectin. Indeed, lectin binding to 6'-SL was inhibited by the most frequently identified mimetic peptide, but not by the reverse or scrambled peptides, showing that this peptide mimics 6'-SL. Functionally, mimetic peptide, but not the reverse or scrambled peptides, increased viability and expression of neural cell adhesion molecule L1 in SK-N-SH human neuroblastoma cells, and promoted survival and neurite outgrowth of cultured mouse cerebellar granule neurons challenged by H₂O₂-induced oxidative stress. The combined results indicate that the 6'-SL mimetic peptide promotes neuronal survival and neuritogenesis, thus raising hopes for the treatment of neurodegenerative diseases. This study was approved by the Medical Ethics Committee of Shantou University Medical College, China (approval No. SUMC 2014-004) on February 20, 2014.

Protective Effects of Costunolide against Hydrogen Peroxide-Induced Injury in PC12 Cells

Oxidative stress-mediated cellular injury has been considered as a major cause of neurodegenerative diseases including Alzheimer’s and Parkinson’s diseases. The scavenging of reactive oxygen species (ROS) mediated by antioxidants may be a potential strategy for retarding the diseases’ progression. Costunolide (CS) is a well-known sesquiterpene lactone, used as a popular herbal remedy, which possesses anti-inflammatory and antioxidant activity. This study aimed to investigate the protective role of CS against the cytotoxicity induced by hydrogen peroxide (H₂O₂) and to elucidate potential protective mechanisms in PC12 cells. The results showed that the treatment of PC12 cells with CS prior to H₂O₂ exposure effectively increased the cell viability. Furthermore, it decreased the intracellular ROS, stabilized the mitochondria membrane potential (MMP), and reduced apoptosis-related protein such as caspase 3. In addition, CS treatment attenuated the cell injury by H₂O₂ through the inhibition of phosphorylation of p38 and the extracellular signal-regulated kinase (ERK). These results demonstrated that CS is promising as a potential therapeutic candidate for neurodegenerative diseases resulting from oxidative damage and further research on this topic should be encouraged.

The potential of synthetic indolylquinoline derivatives for Aβ aggregation reduction by chemical chaperone activity

Alzheimer's disease (AD) is the most prevalent form of dementia associated with progressive cognitive decline and memory loss. Extracellular β-amyloid (Aβ) is a major constituent of senile plaques, one of the pathological hallmarks of AD. Aβ deposition causes neuronal death via a number of possible mechanisms such as increasing oxidative stress. Therefore therapeutic approaches to identify novel Aβ aggregate reducers could be effective for AD treatment. Using a Trx-His-Aβ biochemical assay, we screened 11 synthetic indolylquinoline compounds, and found NC009-1, -2, -6 and -7 displaying potential to reduce Aβ aggregation. Treating Tet-On Aβ-GFP 293 cells with these compounds reduced Aβ aggregation and reactive oxygen species. These compounds also promoted neurite outgrowth in Tet-On Aβ-GFP SH-SY5Y cells. Furthermore, treatment with above compounds improved neuronal cell viability, neurite outgrowth, and synaptophysin expression level in mouse hippocampal primary culture under oligomeric Aβ-induced cytotoxicity. Moreover, the tested NC009-1 significantly ameliorated Aβ-induced inhibition of hippocampal long-term potentiation in mouse hippocampal slices. Our results demonstrate how synthetic indolylquinoline compounds are likely to work as chemical chaperones in Aβ-aggregation reduction and neuroprotection, providing insight into the possible applications of indolylquinoline compounds in AD treatment.

Neuroprotective effects of macranthoin G from Eucommia ulmoides against hydrogen peroxide-induced apoptosis in PC12 cells via inhibiting NF-κB activation

Oxidative stress-mediated cellular injury has been considered as a major cause of neurodegenerative diseases including Alzheimer and Parkinson diseases. The scavenging of reactive oxygen species (ROS) mediated by antioxidants may be a potential strategy for retarding the disease's progression. Macranthoin G (MCG), isolated from Eucommia ulmoides, is a derivative from chlorogenic acid methyl ester and caffeic acid. This study is aimed to investigate the protective role of MCG against the cytotoxicity induced by hydrogen peroxide (H2O2) and to elucidate potential protective mechanisms in rat pheochromocytoma (PC12) cells. The results showed that the treatment of PC12 cells with MCG prior to H2O2 exposure effectively increased the cell viability, and stabilized the mitochondria membrane potential (MMP); furthermore, it enhanced the antioxidant enzyme activities of superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GSH-Px) and the levels of intracellular glutathione (GSH); it also decreased the malondialdehyde (MDA) content, intracellular ROS, caspase-3 activation, as well as cell apoptosis. In addition, the MCG treatment minimized the cell injury by H2O2 via down-regulation of the NF-κB pathway as well as activation of phosphorylation of IκBα, p38, and the extracellular signal-regulated kinase (ERK). These results showed that that MCG is promising as a potential therapeutic agent for neurodegenerative diseases induced by oxidative damage and should be encouraged for further research.

Effects of the exposure to intermittent 1.8 GHz radio frequency electromagnetic fields on HSP70 expression and MAPK signaling pathways in PC12 cells

PURPOSE

We previously reported effects on heat shock protein 70 (HSP70) mRNA expression, a cytoprotective protein induced under stressful condition, in human trophoblast cells exposed to amplitude-modulated Global System for Mobile Communication (GSM) signals. In the present work the same experimental conditions were applied to the rat PC12 cells, in order to assess the stress responses mediated by HSP70 and by the Mitogen Activated Protein Kinases (MAPK) in neuronal-like cells, an interesting model to study possible effects of mobile phone frequencies exposure.

MATERIALS AND METHODS

HSP70 gene expression level was evaluated by reverse transcriptase polymerase chain reaction, HSP70 protein expression and MAPK phosphorylation were assessed by Western blotting. PC12 cells were exposed for 4, 16 or 24 h to 1.8 GHz continuous wave signal (CW, carrier frequency without modulation) or to two different GSM modulation schemes, GSM-217Hz and GSM-Talk (which generates temporal changes between two different GSM signals, active during talking or listening phases, respectively, thus simulating a typical conversation). Specific adsorption rate (SAR) was 2 W/kg.

RESULTS

After PC12 cells exposure to the GSM-217Hz signal for 16 or 24 h, HSP70 transcription significantly increased, whereas no effect was observed in cells exposed to the CW or GSM-Talk signals. HSP70 protein expression and three different MAPK signaling pathways were not affected by the exposure to any of the three different 1.8 GHz signals.

CONCLUSION

The positive effect on HSP70 mRNA expression, observed only in cells exposed to the GSM-217Hz signal, is a repeatable response previously reported in human trophoblast cells and now confirmed in PC12 cells. Further investigations towards a possible role of 1.8 GHz signal modulation are therefore advisable.

Time course study of Aβ formation and neurite outgrowth disruption in differentiated human neuroblastoma cells exposed to H2O2: protective role of autophagy

Here, we tried to elucidate the possible role of autophagy against H2O2 and Amyloid beta (Aβ) induced neurotoxicity using retinoic acid differentiated SH-SY5Y cells. We found that H2O2 disrupted neurite outgrowth concomitant with production of Aβ. Furthermore, we showed that H2O2 could increase the apoptotic factors such as Bax/Bcl-2 ratio, caspase-3 level, and PARP activity in a time course manner. These findings were confirmed by acridine orange/ethidium bromide and Hoechst staining. In addition, we observed that H2O2 led to conversion of LC3 protein from LC3I to LC3II and an increase in autophagy flux. Autophagy factors including LC3B, Atg7, and Atg12 increased and reached their highest level after 2h of insulting and then dropped to a lower level. Our results showed that autophagy could internalize and degrade intra- and extracellular Aβ after 3h treatment with H2O2. However, the remaining amount of Aβ accelerated morphological atrophy and, as a result, increased neuronal death (apoptosis). Inhibition of autophagy influx, using 3-methyl-adenine, increased intra- and extracellular levels of Aβ, providing more proof for a protective role of autophagy against oxidative stress. Further studies can shed light on the important role of autophagy by finding new pathways involved in Aβ degeneration.