• Biomedical Science Letters
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• v.15 no.4
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• pp.327-333
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• 2009

Heterotrimeric GTP binding proteins, G-proteins, mediate signal transduction generated by neurotransmitters and hormones. Among G-proteins, Go proteins are the most abundant in brain and classified as a member of Gi family. Ras-like protein in all tissues (Rit), one of the small GTPases, is a member of a Ras superfamily and identified as an important regulator of neuronal differentiation and cell transformation. Recently, we have reported that Rit functioned as a candidate downstream effector for alpha subunit of Go proteins ($Go{\alpha}$) and regulated neurite outgrowth triggered by $Go{\alpha}$ activation. In this study, we showed that the GTPase domain of $Go{\alpha}$ contributed to the direct interaction with Rit. We also demonstrated that $Go{\alpha}$ could lead to an increase of Rit activity suggesting that Rit play a role as a downstream effector of $Go{\alpha}$.

• The Korean Journal of Physiology and Pharmacology
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• v.21 no.2
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• pp.179-188
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• 2017

With the explosive increase in exposure to radiofrequency electromagnetic fields (RF-EMF) emitted by mobile phones, public concerns have grown over the last few decades with regard to the potential effects of EMF exposure on the nervous system in the brain. Many researchers have suggested that RF-EMFs can effect diverse neuronal alterations in the brain, thereby affecting neuronal functions as well as behavior. Previously, we showed that long-term exposure to 835 MHz RF-EMF induces autophagy in the mice brain. In this study, we explore whether shortterm exposure to RF-EMF leads to the autophagy pathway in the cerebral cortex and brainstem at 835 MHz with a specific absorption rate (SAR) of 4.0 W/kg for 4 weeks. Increased levels of autophagy genes and proteins such as LC3B-II and Beclin1 were demonstrated and the accumulation of autophagosomes and autolysosomes was observed in cortical neurons whereas apoptosis pathways were up-regulated in the brainstem but not in the cortex following 4 weeks of RF exposure. Taken together, the present study indicates that monthly exposure to RF-EMF induces autophagy in the cerebral cortex and suggests that autophagic degradation in cortical neurons against a stress of 835 MHz RF during 4 weeks could correspond to adaptation to the RF stress environment. However, activation of apoptosis rather than autophagy in the brainstem is suggesting the differential responses to the RF-EMF stresses in the brain system.

• The Korean Journal of Physiology and Pharmacology
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• v.15 no.6
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• pp.389-395
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• 2011

Repeated administration of psychostimulants such as cocaine leads to the development of behavioral sensitization. Extracellular signal-Regulated Kinase (ERK), an enzyme important for long-term neuronal plasticity, has been implicated in such effects of these drugs. Although the nucleus accumbens (NAcc) is the site mediating the expression of behavioral sensitization by drugs of abuse, the precise role of ERK activation in this site has not been determined. In this study we demonstrate that blockade of ERK phosphorylation in the NAcc by a single bilateral microinjections of PD98059 (0.5 or $2.0{\mu}g/side$), or U0126 (0.1 or $1.0{\mu}g/side$), into this site dose-dependently inhibited the expression of cocaine-induced behavioral sensitization when measured at day 7 following 6 consecutive daily cocaine injections (15 mg/kg, i.p.). Acute microinjection of either vehicle or PD98059 alone produced no different locomotor activity compared to saline control. Further, microinjection of PD98059 ($2.0{\mu}g/side$) in the NAcc specifically lowered cocaine-induced increase of ERK phosphorylation levels in this site, while unaffecting p-38 protein levels. These results indicate that ERK activation in the NAcc is necessary for the expression of cocaine-induced behavioral sensitization, and further suggest that repeated cocaine evokes neuronal plasticity involving ERK pathway in this site leading to long-lasting behavioral changes.

• The Korean Journal of Physiology and Pharmacology
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• v.24 no.4
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• pp.299-310
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• 2020

Alzheimer's disease (AD) is a multi-faceted neurodegenerative disease. Thus, current therapeutic strategies require multitarget-drug combinations to treat or prevent the disease. At the present time, single drugs have proven to be inadequate in terms of addressing the multifactorial pathology of AD, and multitarget-directed drug design has not been successful. Based on these points of views, it is judged that combinatorial drug therapies that target several pathogenic factors may offer more attractive therapeutic options. Thus, we explored that the combination therapy with lower doses of cilostazol and aripiprazole with add-on donepezil (CAD) might have potential in the pathogenesis of AD. In the present study, we found the superior efficacies of donepezil add-on with combinatorial mixture of cilostazol plus aripiprazole in modulation of expression of AD-relevant genes: Aβ accumulation, GSK-3β, P300, acetylated tau, phosphorylated-tau levels, and activation of α-secretase/ADAM 10 through SIRT1 activation in the N2a Swe cells expressing human APP Swedish mutation (N2a Swe cells). We also assessed that CAD synergistically raised acetylcholine release and choline acetyltransferase (CHAT) expression that were declined by increased β-amyloid level in the activated N2a Swe cells. Consequently, CAD treatment synergistically increased neurite elongation and improved cell viability through activations of PI3K, BDNF, β-catenin and α7-nicotinic cholinergic receptors in neuronal cells in the presence of Aβ_1-42. This work endorses the possibility for efficient treatment of AD by supporting the synergistic therapeutic potential of donepezil add-on therapy in combination with lower doses of cilostazol and aripiprazole.

• Journal of Applied Biological Chemistry
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• v.62 no.4
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• pp.347-353
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• 2019

Stings of jellyfish, which frequently occur in a warm season, cause severe pain, inflammation and sometimes irreversible results such as the death. Harmful venoms from jellyfish, therefore, have been studied for finding the therapeutic agents to relieve pain or to neutralize toxic components. However, it is still unclear if and how jellyfish venom reveal neuronal toxicity even though pain induction seems to result from the activation of nociceptors such as nerve endings. In this study, using HT-22 cell line, we investigated neurotoxic effects of the venom of Chrysaora pacifica (CpV) which appears in South-East ocean of Korea. In 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide assay, CpV significantly reduced the viability of HT-22 cells in a dose-dependent manner. Additionally, in 2',7'-Dichlorofluorescin diacetate fluorescence test under the culture condition lacking dominant inflammatory factors, CpV remarkably increased the production of intracellular reactive oxygen species (ROS). Reduced responsive fluorescence to Rhodamine123 and increased expression of intracellular cytochrome c were also observed in HT-22 cells treated with CpV. These indicate that CpV-reduced viability of HT-22 cells may be due to the activation of apoptotic signalings mediated with oxidative stress and mitochondrial dysfunction. Furthermore, removing Ca²⁺ ion or adding N-acetyl-Lcystein remarkably blocked the CpV effect to reduce the viability of HT-22 cells. The findings in this study clearly demonstrate that CpV may activate Ca²⁺-mediated ROS signalings and mitochondrial dysfunction resulting in neuronal damage or death, and suggest that blocking Ca²⁺ pathway is a therapeutic approach to possibly block toxic effects of jellyfish venoms.

• The Korean Journal of Physiology and Pharmacology
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• v.3 no.1
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• pp.19-27
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• 1999

Apoptosis has been implicated in the pathophysiological mechanisms of various neurodegenerative diseases. In a variety of cell types, oxidative stress has been demonstrated to play an important role in the apoptotic cell death. However, the exact mechanism of oxidative stress-induced apoptosis in neuronal cells is not known. In this study, we induced oxidative stress in IMR-32 human neuroblastoma cells with tert- butylhydroperoxide (TBHP), which was confirmed by significantly reduced glutathione content and glutathione reductase activity, and increased glutathione peroxidase activity. TBHP induced decrease in cell viability and increase in DNA fragmentation, a hallmark of apoptosis, in a dose-dependent manner. TBHP also induced a sustained increase in intracellular $Ca^{2+}$ concentration, which was completely prevented either by EGTA, an extracellular $Ca^{2+}$ chelator or by flufenamic acid (FA), a non-selective cation channel (NSCC) blocker. These results indicate that the TBHP-induced intracellular $Ca^{2+}$ increase may be due to $Ca^{2+}$ influx through the activation of NSCCs. In addition, treatment with either an intracellular $Ca^{2+}$ chelator (BAPTA/AM) or FA significantly suppressed the TBHP-induced apoptosis. Moreover, TBHP increased the expression of p53 gene but decreased c-myc gene expression. Taken together, these results suggest that the oxidative stress-induced apoptosis in neuronal cells may be mediated through the activation of intracellular $Ca^{2+}$ signals and altered expression of p53 and c-myc.

• The Korean Journal of Physiology and Pharmacology
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• v.25 no.2
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• pp.97-109
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• 2021

Neonatal hypoxia/ischemia (H/I), injures white matter, results in neuronal loss, disturbs myelin formation, and neural network development. Neuroinflammation and oxidative stress have been reported in neonatal hypoxic brain injuries. We investigated whether Paeoniflorin treatment reduced H/I-induced inflammation and oxidative stress and improved white matter integrity in a neonatal rodent model. Seven-day old Sprague-Dawley pups were exposed to H/I. Paeoniflorin (6.25, 12.5, or 25 mg/kg body weight) was administered every day via oral gavage from postpartum day 3 (P3) to P14, and an hour before induction of H/I. Pups were sacrificed 24 h (P8) and 72 h (P10) following H/I. Paeoniflorin reduced the apoptosis of neurons and attenuated cerebral infarct volume. Elevated expression of cleaved caspase-3 and Bad were regulated. Paeoniflorin decreased oxidative stress by lowering levels of malondialdehyde and reactive oxygen species generation and while, and it enhanced glutathione content. Microglial activation and the TLR4/NF-κB signaling were significantly down-regulated. The degree of inflammatory mediators (interleukin 1β and tumor necrosis factor-α) were reduced. Paeoniflorin markedly prevented white matter injury via improving expression of myelin binding protein and increasing O1-positive olidgodendrocyte and O4-positive oligodendrocyte counts. The present investigation demonstrates the potent protective efficiency of paeoniflorin supplementation against H/I-induced brain injury by effectually preventing neuronal loss, microglial activation, and white matter injury via reducing oxidative stress and inflammatory pathways.

• International Journal of Oral Biology
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• v.45 no.4
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• pp.179-189
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• 2020

Green tea polyphenol (-)-epigallocatechin-3-gallate (EGCG) is a potent antioxidant with protective effects against neurotoxicity. However, it is currently unclear whether EGCG protects neuronal cells against radiation-induced damage. Therefore, the objective of this study was to investigate the effects of EGCG on ultraviolet (UV)-induced oxidative stress and apoptosis in PC12 cells. The effects of UV irradiation included apoptotic cell death, which was associated with DNA fragmentation, reactive oxygen species (ROS) production, enhanced caspase-3 and caspase-9 activity, and poly (ADP-ribose) polymerase cleavage. UV irradiation also increased the Bax/Bcl-2 ratio and mitochondrial pathway-associated cytochrome c expression. However, pretreatment with EGCG before UV exposure markedly decreased UV-induced DNA fragmentation and ROS production. Furthermore, the UV irradiation-induced increase in Bax/Bcl-2 ratio, cytochrome c upregulation, and caspase-3 and caspase-9 activation were each ameliorated by EGCG pretreatment. Additionally, EGCG suppressed UV-induced phosphorylation of p38 and rescued UV-downregulated phosphorylation of ERK. Taken together, these results suggest that EGCG prevents UV irradiation-induced apoptosis in PC12 cells by scavenging ROS and inhibiting the mitochondrial pathways known to play a crucial role in apoptosis. In addition, EGCG inhibits UV-induced apoptosis via JNK inactivation and ERK activation in PC12 cells. Thus, EGCG represents a potential neuroprotective agent that could be applied to prevent neuronal cell death induced by UV irradiation.

• Journal of Life Science
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• v.21 no.5
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• pp.647-655
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• 2011

The neurotoxicity of aggregated amyloid ${\beta}$ ($A{\beta}$) has been implicated as a critical cause in the pathogenesis of Alzheimer's disease (AD). It can cause neurotoxicity in AD by evoking a cascade of apoptosis to neuron. Here, we investigated the neuroprotective effects of cilostazol, which acts as a phosphodiesterase III inhibitor, on $A{\beta}_{25-35}$-induced cytotoxicity in mouse neuronal cells and cognitive decline in the C57BL/6J AD mouse model via peroxisome proliferator-activated receptor (PPAR)-${\gamma}$ activation. $A{\beta}_{25-35}$ significantly reduced cell viability and increased the number of apoptotic-like cells. Cilostazol treatment recovered cells from $A{\beta}$-induced cell death as well as rosiglitazone, a PPAR-${\gamma}$ activator. These effects were suppressed by GW9662, an antagonist of PPAR-${\gamma}$ activity, indicative of a PPAR-${\gamma}$-mediated signaling. In addition, cilostazol and rosiglitazone also restored PPAR-${\gamma}$ activity levels that had been altered as a result of $A{\beta}_{25-35}$ treatment, which were antagonized by GW9662. Furthermore, cilostazol also markedly decreased the number of apoptotic-like cells and decreased the Bax/Bcl-2 ratio. Intracerebroventricular injection of $A{\beta}_{25-35}$ in C57BL/6J mice resulted in impaired cognitive function. Oral administration of cilostazol (20 mg/kg) for 2 weeks before $A{\beta}_{25-35}$ injection and once a day for 4 weeks post-surgery almost completely prevented the $A{\beta}_{25-35}$-induced cognitive deficits, as did rosiglitazone. Taken together, our findings suggest that cilostazol could attenuate $A{\beta}_{25-35}$-induced neuronal cell injury and apoptosis as well as promote the survival of neuronal cells, subsequently improving cognitive decline in AD, partly because of PPAR-${\gamma}$ activation. The phosphodiesterase III inhibitor cilostazol may be the basis of a novel strategy for the therapy of AD.

• Korean Journal of Acupuncture
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• v.24 no.1
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• pp.131-144
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• 2007

Objectives : Although the cause of neuronal death of Parkinson's disease remains unclear, increasing evidence points to the role of inflammatory processes. And the hallmark of brain inflammation is the activation of microglia. This study was performed to prove the effect of acupuncture on inhibiting microglial activation. Methods : The rat models which were injected with 6-hydroxydopamine were treated with acupuncture once a day on LR3 (太衝) and GB34 (陽陵泉). To prove the effect of inhibiting microglial activation, we examined the tyrosine hydroxylase (TH) immunopositive neurons and CD11b immunohistochemistry in the substantia nigra. Results : There were 18% (third day), 32% (seventh day) loss of TH-positive cell bodies in the control group and 23% (third day), 26% (seventh day) in the acupuncture group, whereas 3% (third day), 10% (seventh day) in vehicle group. The difference of optical density in substantia nigra was evaluated by subtracting log inverse gray value of contralateral side from that of ipsilateral side. With regards to the result of CD11b immunohistochemistry, acupuncture group showed significantly inhibited microglial activation compared with control group (p<0.01) on the seventh day. Conclusions : Acupuncture showed the effect of inhibition of microglial activation in seventh day. However, the effect of protection of TH positive cell bodies was not shown. So we need longer investigation of the effect of acupuncture on Parkinson's disease.