Atorvastatin Rejuvenates Neural Stem Cells Injured by Oxygen-Glucose Deprivation and Induces Neuronal Differentiation Through Activating the PI3K/Akt and ERK Pathways

Choi, Na-Young,Kim, Ji Young,Hwang, Mina,Lee, Eun-Hye,Choi, Hojin,Lee, Kyu-Yong,Lee, Young Joo,Koh, Seong-Ho Springer-Verlag 2019 Molecular neurobiology Vol.56 No.4

Au-doped PtCo/C catalyst preventing Co leaching for proton exchange membrane fuel cells

Choi, Juhyuk,Cho, Jinwon,Roh, Chi-Woo,Kim, Beom-Sik,Choi, Min Suk,Jeong, Hojin,Ham, Hyung Chul,Lee, Hyunjoo Elsevier 2019 Applied catalysis. B, Environmental Vol.247 No.-

<P><B>Abstract</B></P> <P>Proton exchange membrane fuel cells (PEMFCs) are promising mobile power supply systems, and operate without noise or polluting emissions. Because the oxygen reduction reaction (ORR) at the cathode suffers from high overpotential and sluggish kinetics, many catalysts have been developed in efforts to enhance activity and durability for the ORR. However, most of them have complicated synthetic procedures which cannot be scaled-up easily, and have only been tested in a half-cell. High activity in a half-cell does not necessarily guarantee better performance in a single-cell. In this work, we synthesized an Au-doped PtCo/C catalyst using a simple method of gas-phase reduction and subsequent galvanic replacement, and its activity and durability were tested in a single-cell. When current densities were compared at 0.6 V after a durability test of 30,000 cycles in 0.6–1.0 V, the values were 1.40, 0.81, and 0.63 A cm<SUP>−2</SUP> for the Au-doped PtCo/C, acid-treated PtCo/C, and commercial Pt/C catalysts, respectively. Co leaching was much less in the Au-doped PtCo/C. Density functional theory (DFT) calculations confirmed that surface oxygen species bound more weakly at the catalyst surface and migration of a Co atom (Co segregation) to the surface was suppressed in the presence of Au. This facile method can provide a more realistic strategy to design better ORR catalysts for PEMFC application.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Au-doped PtCo/C catalyst was prepared by gas-phase reduction and subsequent galvanic replacement in a gram-scale. </LI> <LI> The Au-doped catalyst showed enhanced activity and durability for ORR in half-cell and single-cell tests. </LI> <LI> The maximum power density after durability tests was 1.12 W cm<SUP>−2</SUP> for Au-doped catalyst and 0.69 W cm<SUP>−2</SUP> for commercial Pt/C. </LI> <LI> DFT calculations confirmed that Co leaching could be suppressed by Au doping at Pt shell. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Electromagnetic dipole coupling mechanism in layered terahertz metamaterials.

Choi, Jeongmook,Jung, Hyunseung,Lee, Hojin,Choi, Hyunyong Optical Society of America 2013 Optics express Vol.21 No.14

<P>Interplay between adjacent dipoles is an experimental priori for designing artificially-engineered structure because the dipole coupling is one critical factor for determining the electromagnetic response in metamaterials. Although numerous investigations have been performed to study the coupling effect of the split-ring resonator (SRR), the interlayer dipole coupling of its complementary SRR, called C-SRR, has been largely unexplored. Here, we present experimental and theoretical investigations on the electromagnetic coupling effect in the two stacks of layered C-SRR structures. By adjusting the relative lateral distance between the two-dimensionally stacked meta-structures, we observe that the confined magnetic dipole plays an important role in determining the resonance frequency and the bandwidth broadening of the C-SRR, exhibiting an exactly opposite behavior to the SRR structure. Our investigation provides experimental basis for developing frequency tunable three-dimensional metamaterial devices.</P>

Candesartan Restores the Amyloid Beta-Inhibited Proliferation of Neural Stem Cells by Activating the Phosphatidylinositol 3-Kinase Pathway

Choi, Hojin,Choi, Na-Young,Lee, Kyu-Yong,Lee, Young Joo,Koh, Seong-Ho Korean Dementia Association 2017 Dementia and Neurocognitive Disorders Vol.16 No.3

<P><B>Background and Purpose</B></P><P>Neurogenesis in the adult brain is important for memory and learning, and the alterations in neural stem cells (NSCs) may be an important aspect of Alzheimer's disease (AD) pathogenesis. The phosphatidylinositol 3-kinase (PI3K) pathway has been suggested to have an important role in neuronal cell survival and is highly involved in adult neurogenesis. Candesartan is an angiotensin II receptor antagonist used for the treatment of hypertension and several studies have reported that it also has some neuroprotective effects. We investigated whether candesartan could restore the amyloid-β(25–35) (Aβ<SUB>25-35</SUB>) oligomer-inhibited proliferation of NSCs by focusing on the PI3K pathway.</P><P><B>Methods</B></P><P>To evaluate the effects of candesartan on the Aβ<SUB>25-35</SUB> oligomer-inhibited proliferation of NSCs, the NSCs were treated with several concentrations of candesartan and/or Aβ<SUB>25-35</SUB> oligomers, and MTT assay and trypan blue staining were performed. To evaluate the effect of candesartan on the Aβ-inhibited proliferation of NSCs, we performed a bromodeoxyuridine (BrdU) labeling assay. The levels of p85α PI3K, phosphorylated Akt (pAkt) (Ser473), phosphorylated glycogen sinthase kinase-3β (pGSK-3β) (Ser9), and heat shock transcription factor-1 (HSTF-1) were analyzed by Western blotting.</P><P><B>Results</B></P><P>The BrdU assays demonstrated that NSC proliferation decreased with Aβ<SUB>25-35</SUB> oligomer treatment; however, a combined treatment with candesartan restored it. Western blotting displayed that candesartan treatment increased the expression levels of p85α PI3K, pAkt (Ser473), pGSK-3β (Ser9), and HSTF. The NSCs were pretreated with a PI3K inhibitor, LY294002; the effects of candesartan on the proliferation of NSCs inhibited by Aβ<SUB>25-35</SUB> oligomers were almost completely blocked.</P><P><B>Conclusions</B></P><P>Together, these results suggest that candesartan restores the Aβ<SUB>25-35</SUB> oligomer-inhibited proliferation of NSCs by activating the PI3K pathway.</P>

Air Pollution and Dementia

Hojin Choi,김승현 대한치매학회 2019 Dementia and Neurocognitive Disorders Vol.18 No.4

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Coronavirus Disease 2019 and Dementia: The Survey for Dementia Patients in COVID-19 Crisis

Choi Hojin,Lim Jae-Sung,Lee Chan-Nyoung,장재원,이상학,Na Seunghee,Ryoo Nayoung,Park Kun Woo,Shim Yong S. 대한치매학회 2021 Dementia and Neurocognitive Disorders Vol.20 No.2

Understanding the role of glycogen synthase kinase-3 in L-DOPA-induced dyskinesia in Parkinson’s disease

Choi, Hojin,Koh, Seong-Ho Informa UK (Taylor Francis) 2018 Expert opinion on drug metabolism & toxicology Vol.14 No.1

<P>Expert opinion: GSK-3 plays critical roles in L-DOPA-induced neurotoxicity, and the development of specific methods to inhibit GSK-3 function may help prevent L-DOPA neurotoxicity and LID in PD. However, balanced GSK-3 inhibition and less beta-catenin degradation is essential for preventing LID, because too much GSK-3 inhibition increases beta-catenin levels, which is related to cancers.</P>

마하5급 스크램제트 연소기에서 운용조건 변화에 따른 화염특성 연구

최호진(Hojin Choi),김재원(Jaewon Kim),진상욱(Sangwook Jin),배주현(Juhyun Bae),변종열(Jong-Ryul Byun) 한국추진공학회 2022 한국추진공학회 학술대회논문집 Vol.2022 No.11

「황토기」의 구조와 미적가치

최호진(Choi, Hojin) 전남대학교 한국어문학연구소 2013 전남대학교 한국어문학연구소 학술지 어문논총 Vol.- No.24

「황토기」는 그동안 연구된 김동리 문학의 주된 특질을 포함한다. 본고는 기존연구를 바탕으로 「황토기」를 내재적, 외재적 관점에서 종합적으로 분석해 독특한 미적가치를 추출해보고자 한다. 김동리는 민족의 울분과 한을 민족적인 소재로 상징화했는데 그가 차용한 토속 신화 모티프는 일제에 강탈된 조국의 신화라는 정치적인 의미가 심층구조를 이룬다. 일제의 식민지 지배이데올로기가 정점에 이르렀던 1940년에 쓴 「황토기」는 표층구조뿐 아니라 이러한 심층구조를 종합적으로 분석할 필요가 있다. 「황토기」는 풍수설화인 상룡설(傷龍設), 쌍룡설(雙龍設), 절맥설(切脈設) 모티프가 표층구조를 이룬다. 도입부에서 세 가지 풍수설화를 제시한 것은 일종의 도입 액자를 구성하려는 의도적 플롯으로 이는 내부이야기의 ‘운명론적 허무구조’를 말하려는 조치이다. 황토골의 지리적 배경과 두 용의 운명은 이민족과의 갈등, 대립, 끊임없이 투쟁해야 하는 ‘민족의 숙명성’을 상징한다고 볼 수 있다. 내부이야기의 의미기능은 억쇠가 세계 내에서 어떻게 허무를 인식하고 저항, 투신하는가로 집약할 수 있다. 「황토기」의 심층구조는 민간설화로 이야기하려던 민족의 정체성과 민족의 현재, 미래를 시대와의 길항관계로 심층구조에 은폐할 수밖에 없었던 역사적 상징구조와 김동리의 개인적 무의식에서 형성된 정신적 결핍이 집단 무의식과 합류하면서 발생하는 개인적 상징구조로 살필 수 있다. 김동리 문학에서 죽음은 ‘구경적 삶’에 도달하는 데 반드시 거쳐야 할 통과절차이다. 죽음은 ‘구경적 삶’을 완성하기 위해, ‘운명의 전개 과정’과 ‘자연과 동화과정’을 매개하는 하나의 사건이다. 죽음이란 최후적이고 체험될 수 없는 사건이 아니라 오히려 삶 속에 존재하는 것이며, 삶 자체의 요소가 된다. 죽음은 자신을 감추기 위해서 늘 드러내는 방식으로 끊임없이 생을 좇는다. 이는 끊임없이 자신을 분출하는 죽음충동으로부터 송두리째 자신을 생의 충동으로 전이하는 순간의 전율이기도 하다. 이러한 김동리의 죽음 인식은 억쇠와 득보의 싸움을 통해 독특한 숭고미를 이루는데 이는 설화모티프의 토속성과 플롯의 표층과 심층에서 다양하게 이루어지는 상징성과 함께 「황토기」의 미적가치를 높인다는 것을 알 수 있다. 「Hwangtogi」 contains main features of Mr. Kim, Dongri’s literature. This study is trying to analyze the artistic value of his works in the comprehensive way from the internal and external perspective based on the prior studies on his literature. Kim Dongri tried to symbolize the Korean people’s anger and resentment as his motive of the literature. The folklore motive he borrowed for his literature is his fatherland’s myth stolen by Japanese imperialism. This political background constitutes the main theme of his literature. 「Hwangtogi」was written in 1940 when the Japanese imperialism was at its peak. So, we need to analyze his book not only from superficial perspective but also from the deep perspective for comprehensive analysis. 「Hwangtogi」is based on Pengshui folklores such as Sangyongseol, Ssangryeongseol and Jeolmaekseol. The suggestion of three motives in the introductory part of the book is because he tried to organize the introductory frame, intending to tell the ‘structure of fateful unworthiness” of the story. The geographical background of 「Hwangtogi」 and the fate of two dragons seem to symbolize the people’ fate, which was supposed to suffer from the conflict and struggle with other people. The story can be summarized in how Eoksoi, a main character of the story recognizes the unworthiness and resist against it and kill himself. The in-depth structure of 「Hwangtogi」is made of the relation of conflict between Korean people’s identity expressed in the folklore and the situation ofKorean people in the present and future. His symbolic structure is evident when the history which had to be hidden and Kim Dongri’s individual mental deficiency caused by his personal unconsciousness meet collective unconsciousness To complete that life, the death is one event which mediates “the life’s development procedure” and “the procedure of assimilation with nature”. Here, the death is not the final thing which we cannot experience but it is the life itself and an element of life. The death endlessly tracks the life in a way that it exposes itself to hide itself. This is the tremor felt at the moment when a person’s impulse toward death is converted to the impulse of life. This kind of view on the death is accomplished by the fight between Eoksoi and Deukbo. Along with the symbolisms expressed in the superficial and deep structure of folklore and plot, it enhances the artistic value of 「Hwangtogi」.

액체연료를 분사하는 파일론 연료분사장치를 적용한 초음속 연소기의 화염특성 연구

최호진(Hojin Choi),김재원(Jaewon Kim),진상욱(Sangwook Jin),변종열(Jong-Ryul Byun),박동창 한국추진공학회 2023 한국추진공학회 학술대회논문집 Vol.2023 No.5