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Ignatova I, Frolov R, Nymark S. The retinal pigment epithelium displays electrical excitability and lateral signal spreading. BMC Biol 2023; 21:84. [PMID: 37069561 PMCID: PMC10111697 DOI: 10.1186/s12915-023-01559-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2022] [Accepted: 03/10/2023] [Indexed: 04/19/2023] Open
Abstract
BACKGROUND The non-neuronal retinal pigment epithelium (RPE) functions in intimate association with retinal photoreceptors, performing a multitude of tasks critical for maintaining retinal homeostasis and collaborating with retinal glial cells to provide metabolic support and ionic buffering. Accordingly, the RPE has recently been shown to display dynamic properties mediated by an array of ion channels usually more characteristic of astrocytes and excitable cells. The recent discovery of canonical voltage-activated Na+ channels in the RPE and their importance for phagocytosis of photoreceptor outer segments raises a question about their electrogenic function. Here, we performed a detailed electrophysiological analysis related to the functioning of these channels in human embryonic stem cell (hESC)-derived RPE. RESULTS Our studies examining the electrical properties of the hESC-RPE revealed that its membrane mainly displays passive properties in a broad voltage range, with the exception of depolarization-induced spikes caused by voltage-activated Na+ current (INa). Spike amplitude depended on the availability of INa and spike kinetics on the membrane time constant, and the spikes could be largely suppressed by TTX. Membrane resistance fluctuated rapidly and strongly, repeatedly changing over the course of recordings and causing closely correlated fluctuations in resting membrane potential. In a minority of cells, we found delayed secondary INa-like inward currents characterized by comparatively small amplitudes and slow kinetics, which produced secondary depolarizing spikes. Up to three consecutive delayed inward current waves were detected. These currents could be rapidly and reversibly augmented by applying L-type Ca2+ channel blocker nifedipine to diminish influx of calcium and thus increase gap junctional conductance. CONCLUSIONS This work shows, for the first time, that INa and INa-mediated voltage spikes can spread laterally through gap junctions in the monolayer of cells that are traditionally considered non-excitable. Our findings support a potential role of the RPE that goes beyond giving homeostatic support to the retina.
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Affiliation(s)
- Irina Ignatova
- Faculty of Medicine and Health Technology, Tampere University, Tampere, Finland
| | | | - Soile Nymark
- Faculty of Medicine and Health Technology, Tampere University, Tampere, Finland.
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Lengyel M, Enyedi P, Czirják G. Negative Influence by the Force: Mechanically Induced Hyperpolarization via K 2P Background Potassium Channels. Int J Mol Sci 2021; 22:ijms22169062. [PMID: 34445768 PMCID: PMC8396510 DOI: 10.3390/ijms22169062] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2021] [Revised: 08/19/2021] [Accepted: 08/20/2021] [Indexed: 02/08/2023] Open
Abstract
The two-pore domain K2P subunits form background (leak) potassium channels, which are characterized by constitutive, although not necessarily constant activity, at all membrane potential values. Among the fifteen pore-forming K2P subunits encoded by the KCNK genes, the three members of the TREK subfamily, TREK-1, TREK-2, and TRAAK are mechanosensitive ion channels. Mechanically induced opening of these channels generally results in outward K+ current under physiological conditions, with consequent hyperpolarization and inhibition of membrane potential-dependent cellular functions. In the past decade, great advances have been made in the investigation of the molecular determinants of mechanosensation, and members of the TREK subfamily have emerged among the best-understood examples of mammalian ion channels directly influenced by the tension of the phospholipid bilayer. In parallel, the crucial contribution of mechano-gated TREK channels to the regulation of membrane potential in several cell types has been reported. In this review, we summarize the general principles underlying the mechanical activation of K2P channels, and focus on the physiological roles of mechanically induced hyperpolarization.
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Singh S, Agarwal P, Ravichandiran V. Two-Pore Domain Potassium Channel in Neurological Disorders. J Membr Biol 2021; 254:367-380. [PMID: 34169340 DOI: 10.1007/s00232-021-00189-8] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2021] [Accepted: 05/26/2021] [Indexed: 01/10/2023]
Abstract
K2P channel is the leaky potassium channel that is critical to keep up the negative resting membrane potential for legitimate electrical conductivity of the excitable tissues. Recently, many substances and medication elements are discovered that could either straightforwardly or in a roundabout way influence the 15 distinctive K+ ion channels including TWIK, TREK, TASK, TALK, THIK, and TRESK. Opening and shutting of these channels or any adjustment in their conduct is thought to alter the pathophysiological condition of CNS. There is no document available till now to explain in detail about the molecular mechanism of agents acting on K2P channel. Accordingly, in this review we cover the current research and mechanism of action of these channels, we have also tried to mention the detailed effect of drugs and how the channel behavior changes by focusing on recent advances regarding activation and modulation of ion channels.
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Affiliation(s)
- Sanjiv Singh
- Department of Pharmacology and Toxicology, National Institute of Pharmaceutical Education and Research (NIPER), Export Promotions Industrial Park (EPIP), Industrial Area, Hajipur, District, Vaishali, 844102, Bihar, India.
| | - Punita Agarwal
- Department of Pharmacology and Toxicology, National Institute of Pharmaceutical Education and Research (NIPER), Export Promotions Industrial Park (EPIP), Industrial Area, Hajipur, District, Vaishali, 844102, Bihar, India
| | - V Ravichandiran
- Department of Pharmacology and Toxicology, National Institute of Pharmaceutical Education and Research (NIPER), Export Promotions Industrial Park (EPIP), Industrial Area, Hajipur, District, Vaishali, 844102, Bihar, India
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Kim ST, Chung YY, Hwang HI, Shin HK, Choi R, Jun YH. Differential Expression of BDNF and BIM in Streptozotocin-induced Diabetic Rat Retina After Fluoxetine Injection. In Vivo 2021; 35:1461-1466. [PMID: 33910823 DOI: 10.21873/invivo.12398] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2021] [Revised: 02/04/2021] [Accepted: 02/05/2021] [Indexed: 02/07/2023]
Abstract
BACKGROUND Chronic diabetic retinopathy (DR) is a diabetic complication that causes blindness. Brain-derived neurotrophic factor (BDNF) expression is induced by fluoxetine. We observed the effects of fluoxetine on a streptozotocin (STZ)-induced diabetic rat model in this study. MATERIALS AND METHODS Rats were divided into three groups: Control, diabetic (65 mg/kg STZ injection), and diabetic with fluoxetine injection (20 mg/kg/week, six times). Western blotting was performed using anti-BDNF and anti-hexaribonucleotide-binding protein-3. Expression of BCL2 apoptosis regulator-like protein 11 (BIM) was analysed using a reverse transcription-polymerase chain reaction. RESULTS BDNF levels were significantly higher in the diabetic group treated with fluoxetine than in the untreated diabetic group. BIM expression was higher in the diabetic group than in the control group. BIM gene expression was lower in fluoxetine-treated diabetic group than in the untreated diabetic group. CONCLUSION Fluoxetine had an anti-apoptotic effect with upregulation of BDNF expression in retina of rats with STZ-induced diabetes.
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Affiliation(s)
- Seong Taeck Kim
- Department of Ophthalmology, Chosun University Hospital, Gwangju, Republic of Korea
| | - Yoon Young Chung
- Department of Anatomy, School of Medicine, Chosun University, Gwangju, Republic of Korea
| | - Hyo-In Hwang
- Department of Anatomy, School of Medicine, Chosun University, Gwangju, Republic of Korea
| | - Hye-Kyoung Shin
- Department of Anatomy, School of Medicine, Chosun University, Gwangju, Republic of Korea
| | - Ranju Choi
- School of Medicine, Chosun University, Gwangju, Republic of Korea
| | - Yong Hyun Jun
- Department of Anatomy, School of Medicine, Chosun University, Gwangju, Republic of Korea;
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Zhang Z, Yan B, Gao F, Li Q, Meng X, Chen P, Zhou L, Deng W, Li C, Xu W, Han S, Feng H, Li Y, Chen J, Yin Z, Liao C, Tse HF, Xu A, Lian Q. PSCs Reveal PUFA-Provoked Mitochondrial Stress as a Central Node Potentiating RPE Degeneration in Bietti's Crystalline Dystrophy. Mol Ther 2020; 28:2642-2661. [PMID: 32755565 PMCID: PMC7704739 DOI: 10.1016/j.ymthe.2020.07.024] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2020] [Revised: 05/25/2020] [Accepted: 07/21/2020] [Indexed: 12/21/2022] Open
Abstract
Bietti’s crystalline dystrophy (BCD) is an incurable retinal disorder caused by the polypeptide 2 of cytochrome P450 family 4 subfamily V (CYP4V2) mutations. Patients with BCD present degeneration of retinal pigmented epithelial (RPE) cells and consequent blindness. The lack of appropriate disease models and patients’ RPE cells limits our understanding of the pathological mechanism of RPE degeneration. In this study, using CYP4V2 mutant pluripotent stem cells as disease models, we demonstrated that RPE cells with CYP4V2 mutations presented a disrupted fatty acid homeostasis, which were characterized with excessive accumulation of poly-unsaturated fatty acid (PUFA), including arachidonic acid (AA) and eicosapentaenoic acid (EPA). The PUFA overload increased mitochondrial reactive oxygen species, impaired mitochondrial respiratory functions, and triggered mitochondrial stress-activated p53-independent apoptosis in CYP4V2 mutant RPE cells. Restoration of the mutant CYP4V2 using adeno-associated virus 2 (AAV2) can effectively reduce PUFA deposition, alleviate mitochondria oxidative stresses, and rescue RPE cell death in BCD RPE cells. Taken together, our results highlight a role of PUFA-induced mitochondrial damage as a central node to potentiate RPE degeneration in BCD patients. AAV2-mediated gene therapy may represent a feasible strategy for the treatment of BCD.
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Affiliation(s)
- Zhao Zhang
- Department of Medicine, LKS Faculty of Medicine, The University of Hong Kong, Hong Kong SAR, China; Prenatal Diagnostic Centre and Cord Blood Bank, Guangzhou Women and Children's Medical Center, Guangzhou Medical University, Guangzhou 510623, China
| | - Bin Yan
- Department of Computer Science, The University of Hong Kong, Hong Kong SAR, China; School of Biomedical Sciences, The University of Hong Kong, Hong Kong SAR, China; Intervention and Cell Therapy Center, Peking University Shenzhen Hospital, Shenzhen 518036, China
| | - Fei Gao
- Department of Medicine, LKS Faculty of Medicine, The University of Hong Kong, Hong Kong SAR, China
| | - Qing Li
- Ophthalmology, Grantham Hospital, Hospital Authority, Hong Kong SAR, China
| | - Xiaohong Meng
- Southwest Eye Hospital, Third Military Medical University, Chongqing 400038, China
| | - Peikai Chen
- School of Biomedical Sciences, The University of Hong Kong, Hong Kong SAR, China
| | - Lei Zhou
- School of Biomedical Sciences, The University of Hong Kong, Hong Kong SAR, China
| | - Wen Deng
- School of Biomedical Sciences, The University of Hong Kong, Hong Kong SAR, China
| | - Cheng Li
- Department of Medicine, LKS Faculty of Medicine, The University of Hong Kong, Hong Kong SAR, China
| | - Weiyi Xu
- School of Biomedical Sciences, The University of Hong Kong, Hong Kong SAR, China
| | - Shuo Han
- Department of Medicine, LKS Faculty of Medicine, The University of Hong Kong, Hong Kong SAR, China
| | - Hong Feng
- Department of Medicine, LKS Faculty of Medicine, The University of Hong Kong, Hong Kong SAR, China
| | - Yaping Li
- Ophthalmology, The Second Hospital of Jilin University, Changchun 130022, China
| | - Junhui Chen
- Intervention and Cell Therapy Center, Peking University Shenzhen Hospital, Shenzhen 518036, China
| | - Zhengqin Yin
- Southwest Eye Hospital, Third Military Medical University, Chongqing 400038, China
| | - Can Liao
- Prenatal Diagnostic Centre and Cord Blood Bank, Guangzhou Women and Children's Medical Center, Guangzhou Medical University, Guangzhou 510623, China
| | - Hung-Fat Tse
- Department of Medicine, LKS Faculty of Medicine, The University of Hong Kong, Hong Kong SAR, China.
| | - Aimin Xu
- Department of Medicine, LKS Faculty of Medicine, The University of Hong Kong, Hong Kong SAR, China; State Key Laboratory of Pharmaceutical Biotechnology, The University of Hong Kong, Hong Kong SAR, China.
| | - Qizhou Lian
- Department of Medicine, LKS Faculty of Medicine, The University of Hong Kong, Hong Kong SAR, China; Prenatal Diagnostic Centre and Cord Blood Bank, Guangzhou Women and Children's Medical Center, Guangzhou Medical University, Guangzhou 510623, China; State Key Laboratory of Pharmaceutical Biotechnology, The University of Hong Kong, Hong Kong SAR, China.
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Effect of 6-Shogaol on the Glucose Uptake and Survival of HT1080 Fibrosarcoma Cells. Pharmaceuticals (Basel) 2019; 12:ph12030131. [PMID: 31505728 PMCID: PMC6789756 DOI: 10.3390/ph12030131] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2019] [Revised: 08/10/2019] [Accepted: 09/03/2019] [Indexed: 12/29/2022] Open
Abstract
Ginger is a plant that is native to southern China. In the last decade and research on the components of ginger has significantly increased; of these components, 6-shogaol exhibits the greatest potential antitumor capacity. However, the molecular mechanism through which 6-shogaol exerts its effects has not yet been elucidated. In this study, the effect of 6-shogaol on tumor cells that were derived from human fibrosarcoma (HT1080) was evaluated. Cell viability was determined by a (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) MTT assay testing different concentrations of 6-shogaol (2.5–150 μM). Subsequently, the effect of 6-shogaol on reactive oxygen species (ROS) production, glucose uptake, and protein expression of the signaling pathway phosphatase and tensin homolog/ protein kinase B /mammalian target of rapamycin (PTEN/Akt/mTOR) was measured. 6-Shogaol reduced the viability of the tumor cells and caused an increase in ROS production, which was attenuated with the addition of N-acetylcysteine, and the recovery of cell viability was observed. The increase in ROS production in response to 6-shogaol was associated with cell death. Similarly, glucose uptake decreased with incremental concentrations of 6-shogaol, and an increase in the expression of mTOR-p and Akt-p proteins was observed; PTEN was active in all the treatments with 6-shogaol. Thus, the results suggest that cells activate uncontrolled signaling pathways, such as phosphoinositide 3-kinase (PI3K)/Akt/mTOR, among other alternative mechanisms of metabolic modulation and of survival in order to counteract the pro-oxidant effect of 6-shogaol and the decrease in glucose uptake. Interestingly, a differential response was observed when non-cancerous cells were treated with 6-shogaol.
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Wang L, Shi KP, Li H, Huang H, Wu WB, Cai CS, Zhang XT, Zhu XB. Activation of the TRAAK two-pore domain potassium channels in rd1 mice protects photoreceptor cells from apoptosis. Int J Ophthalmol 2019; 12:1243-1249. [PMID: 31456913 DOI: 10.18240/ijo.2019.08.03] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2019] [Accepted: 07/24/2019] [Indexed: 11/23/2022] Open
Abstract
AIM To investigate the expression of TWIK-related arachidonic acid-stimulated K+ channel (TRAAK) in retinal degeneration mice (rd1) and further evaluate how TRAAK affect photoreceptor cell apoptosis. METHODS The rd1 mice were distributed into blank (no treatment), control (1.4% DMSO, intraperitoneal injection) and riluzole groups (4 mg/kg·d, intraperitoneal injection) from postnatal 7d to 10, 14 and 18d; C57 group (no treatment), as age-matched wild-type control. The thickness of the outer nuclear layer (ONL) of retina was detected by paraffin section hematoxylin and eosin staining. The expression of TRAAK and the apoptosis of the ONL cells were detected by immunostaining, Western blotting, and real-time polymerase chain reaction. RESULTS The channel agonist riluzole activated TRAAK and delayed the apoptosis of photoreceptor cells in ONL layer of rd1 mice. Both at mRNA and protein levels, after riluzole treatment, TRAAK expression was significantly upregulated, when compared with the control and blank group. Then we detected a series of apoptosis related mRNA and protein. The anti-apoptotic factor Bcl-2 downregulated and the pro-apoptotic factors Bax and cleaved-caspase-3 upregulated significantly. CONCLUSION Riluzole elevates the expression of TRAAK and inhibits the development of apoptosis. Activation of TRAAK may have some potential effects to put off photoreceptor apoptosis.
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Affiliation(s)
- Lei Wang
- State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou 510060, Guangdong Province, China
| | - Kang-Pei Shi
- State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou 510060, Guangdong Province, China
| | - Han Li
- State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou 510060, Guangdong Province, China
| | - Hao Huang
- State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou 510060, Guangdong Province, China
| | - Wen-Bin Wu
- State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou 510060, Guangdong Province, China
| | - Chu-Sheng Cai
- State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou 510060, Guangdong Province, China
| | - Xiao-Tong Zhang
- State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou 510060, Guangdong Province, China
| | - Xiao-Bo Zhu
- State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou 510060, Guangdong Province, China
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Zhang XT, Xu Z, Shi KP, Guo DL, Li H, Wang L, Zhu XB. Elevated expression of TREK-TRAAK K 2P channels in the retina of adult rd1 mice. Int J Ophthalmol 2019; 12:924-929. [PMID: 31236347 DOI: 10.18240/ijo.2019.06.07] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2018] [Accepted: 04/28/2019] [Indexed: 11/23/2022] Open
Abstract
AIM To examine the expression of Twik-related K+ channel 1 (TREK-1), Twik-related K+ channel 2 (TREK-2), and Twik-related arachidonic acid-stimulated K+ channel (TRAAK) in the retina of adult rd1 mice and to detect the protective roles of TREK-TRAAK two-pore-domain K+ (K2P) channels against retinal degeneration. METHODS Twenty-eight-day-old C57BL/6J mice and 28-day-old rd1 mice were used in this study. Retinal protein, retinal RNA, and embedded eyeballs were prepared from these two groups of mice. Real-time quantitative polymerase chain reaction and Western blot analyses were used to assess the gene transcription and protein levels, respectively. Retinal structures were observed using hematoxylin and eosin (H&E) staining. Immunohistochemistry was utilized to observe the retinal localization of TREK-TRAAK channels. Current changes in retinal ganglion cells (RGCs) after activation of TREK-TRAAK channels were examined using a patch-clamp technique. RESULTS Compared with C57BL/6J mice, rd1 mice exhibited significantly higher retinal mRNA and protein expression levels of TREK-1, TREK-2, and TRAAK channels. In both groups, immunohistochemistry showed expression of TREK-TRAAK channels in retinal layers. After addition of the TREK-TRAAK channel agonist arachidonic acid (AA), whole-cell voltage step evoked currents were significantly higher in RGCs from rd1 mice than in RGCs from control C57BL/6J mice, suggesting that TREK-TRAAK channels were opened in RGCs from rd1 mice. CONCLUSION TREK-TRAAK K2P channels' expression is increased in adult rd1 mice. AA induced the opening of TREK-TRAAK K2P channels in adult rd1 mice and may thus counterbalance depolarization of RGCs and protect the retina from excitotoxicity. TREK-TRAAK channels may play a protective role against retinal degeneration.
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Affiliation(s)
- Xiao-Tong Zhang
- State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou, 510060, Guangdong Province, China
| | - Zhen Xu
- State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou, 510060, Guangdong Province, China
| | - Kang-Pei Shi
- State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou, 510060, Guangdong Province, China
| | - Dian-Lei Guo
- State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou, 510060, Guangdong Province, China
| | - Han Li
- State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou, 510060, Guangdong Province, China
| | - Lei Wang
- State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou, 510060, Guangdong Province, China
| | - Xiao-Bo Zhu
- State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou, 510060, Guangdong Province, China
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