Publications by authors named "Hwan Tae Park"

84 Publications

Guidelines for the use and interpretation of assays for monitoring autophagy (4th edition).

Autophagy 2021 Jan 8;17(1):1-382. Epub 2021 Feb 8.

University of Crete, School of Medicine, Laboratory of Clinical Microbiology and Microbial Pathogenesis, Voutes, Heraklion, Crete, Greece; Foundation for Research and Technology, Institute of Molecular Biology and Biotechnology (IMBB), Heraklion, Crete, Greece.

In 2008, we published the first set of guidelines for standardizing research in autophagy. Since then, this topic has received increasing attention, and many scientists have entered the field. Our knowledge base and relevant new technologies have also been expanding. Thus, it is important to formulate on a regular basis updated guidelines for monitoring autophagy in different organisms. Despite numerous reviews, there continues to be confusion regarding acceptable methods to evaluate autophagy, especially in multicellular eukaryotes. Here, we present a set of guidelines for investigators to select and interpret methods to examine autophagy and related processes, and for reviewers to provide realistic and reasonable critiques of reports that are focused on these processes. These guidelines are not meant to be a dogmatic set of rules, because the appropriateness of any assay largely depends on the question being asked and the system being used. Moreover, no individual assay is perfect for every situation, calling for the use of multiple techniques to properly monitor autophagy in each experimental setting. Finally, several core components of the autophagy machinery have been implicated in distinct autophagic processes (canonical and noncanonical autophagy), implying that genetic approaches to block autophagy should rely on targeting two or more autophagy-related genes that ideally participate in distinct steps of the pathway. Along similar lines, because multiple proteins involved in autophagy also regulate other cellular pathways including apoptosis, not all of them can be used as a specific marker for autophagic responses. Here, we critically discuss current methods of assessing autophagy and the information they can, or cannot, provide. Our ultimate goal is to encourage intellectual and technical innovation in the field.
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http://dx.doi.org/10.1080/15548627.2020.1797280DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7996087PMC
January 2021

Potential neuron-autonomous Purkinje cell degeneration by 2',3'-cyclic nucleotide 3'-phosphodiesterase promoter/Cre-mediated autophagy impairments.

FASEB J 2021 Jan;35(1):e21225

Peripheral Neuropathy Research Center (PNRC), Department of Molecular Neuroscience, College of Medicine, Department of Translational Biomedical Sciences, Graduate School of Dong-A University, Dong-A University, Busan, Republic of Korea.

Studies of neuroglial interaction largely depend on cell-specific gene knockout (KO) experiments using Cre recombinase. However, genes known as glial-specific genes have recently been reported to be expressed in neuroglial stem cells, leading to the possibility that a glia-specific Cre driver results in unwanted gene deletion in neurons, which may affect sound interpretation. 2',3'-Cyclic nucleotide 3'-phosphodiesterase (CNP) is generally considered to be an oligodendrocyte (OL) marker. Accordingly, Cnp promoter-controlled Cre recombinase has been used to create OL-specific gene targeting mice. However, in this study, using Rosa26-tdTomato-reporter/Cnp-Cre mice, we found that many forebrain neurons and cerebellar Purkinje neurons belong to the lineages of Cnp-expressing neuroglial stem cells. To answer whether gene targeting by Cnp-Cre can induce neuron-autonomous defects, we conditionally deleted an essential autophagy gene, Atg7, in Cnp-Cre mice. The Cnp-Cre-mediated Atg7 KO mice showed extensive p62 inclusion in neurons, including cerebellar Purkinje neurons with extensive neurodegeneration. Furthermore, neuronal areas showing p62 inclusion in Cnp-Cre-mediated Atg7 KO mice overlapped with the neuronal lineage of Cnp-expressing neuroglial stem cells. Moreover, Cnp-Cre-mediated Atg7-KO mice did not develop critical defects in myelination. Our results demonstrate that a large population of central neurons are derived from Cnp-expressing neuroglial stem cells; thus, conditional gene targeting using the Cnp promoter, which is known to be OL-specific, can induce neuron-autonomous phenotypes.
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http://dx.doi.org/10.1096/fj.202001366RRDOI Listing
January 2021

Finger drop sign as a new variant of acute motor axonal neuropathy.

Muscle Nerve 2021 03 22;63(3):336-343. Epub 2020 Dec 22.

Department of Neurology, Dong-A University College of Medicine, Busan, Republic of Korea.

We propose the finger drop sign as a new clinical variant of acute motor axonal neuropathy (AMAN) defined by immunological and radiological evidence. We identified eight consecutive patients who had AMAN. All of them developed prominent involvement of the finger extensors. We performed magnetic resonance imaging (MRI) of the extremity muscles and serological assays for antiganglioside antibodies and Campylobacter jejuni. Patients with AMAN showed characteristic and a markedly sustained weakness of the finger extensors with a distinctive pattern of the finger drop sign. Limb MRI revealed unevenly distributed abnormal signals in the muscles mainly innervated by the posterior interosseous nerve. All tested patients showed positivity for immunoglobulin G antibody against ganglioside complex of GM1 and phosphatidic acid. A pathophysiological understanding of this unique syndrome can provide further insight into antiganglioside-antibody-mediated axonal injury in Guillain-Barré syndrome.
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http://dx.doi.org/10.1002/mus.27126DOI Listing
March 2021

Exosomes derived from differentiated Schwann cells inhibit Schwann cell migration via microRNAs.

Neuroreport 2020 05;31(7):515-522

Department of Molecular Neuroscience, College of Medicine, Dong-A University, Busan, South Korea.

Exosomes derived from Schwann cells have been known to have a variety of functions in the development and repair of the peripheral nervous system, and cyclic AMP (cAMP) is a key inducer of Schwann cell differentiation. In the present study, we aimed to study the effect of exosomes derived from differentiated Schwann cells on the expression of microRNAs (miRNAs). To show that miRNAs were altered from exosomes derived from Schwann cells, we conducted next-generation sequencing (NGS) arrays with exosomes derived from cAMP-induced differentiated Schwann cells and control. NGS arrays revealed that 22 miRNAs, 33 small nucleolar RNAs, one antisense RNA, and two mRNAs were upregulated, while 37 mRNAs, one tRNA, and 35 antisense RNAs were downregulated. We also confirmed that miRNA211 and miR92a-3p were upregulated, while the expression levels of hypoxia-inducible factor, rat cyclin-dependent kinase 2, and rat platelet-derived growth factor C were reduced in exosomes derived from cAMP-induced differentiated Schwann cells. Venn diagrams were used to identify overlapping miRNA targets from highly expressed miRNAs (miR211-5p, miR211-3p, and miR92a-3p). The pathways identified via Kyoto Encyclopedia of Genes and Genomes analysis of the target genes are associated with nerve regeneration and Schwann cell proliferation such as the tumor necrosis factor signaling pathway, dopaminergic synapse, and neurotrophin signaling, and cAMP-dependent signaling pathways. Additionally, we observed that exosomes derived from differentiated Schwann cells suppressed Schwann cell migration, while control exosomes obtained from undifferentiated Schwann cells did not. Together, the results suggested that exosomes released from differentiated Schwann cells regulated Schwann cell migration through changes in miRNA expression.
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http://dx.doi.org/10.1097/WNR.0000000000001435DOI Listing
May 2020

Loss-of-function of EBP50 is a new cause of hereditary peripheral neuropathy: EBP50 functions in peripheral nerve system.

Glia 2020 09 20;68(9):1794-1809. Epub 2020 Feb 20.

Department of Pharmacology, Brain Science and Engineering Institute, BK21 Plus KNU Biomedical Convergence Program, School of Medicine, Kyungpook National University, Daegu, Republic of Korea.

Finding causative genetic mutations is important in the diagnosis and treatment of hereditary peripheral neuropathies. This study was conducted to find new genes involved in the pathophysiology of hereditary peripheral neuropathy. We identified a new mutation in the EBP50 gene, which is co-segregated with neuropathic phenotypes, including motor and sensory deficit in a family with Charcot-Marie-Tooth disease. EBP50 is known to be important for the formation of microvilli in epithelial cells, and the discovery of this gene mutation allowed us to study the function of EBP50 in the nervous system. EBP50 was strongly expressed in the nodal and paranodal regions of sciatic nerve fibers, where Schwann cell microvilli contact the axolemma, and at the growth tips of primary Schwann cells. In addition, EBP50 expression was decreased in mouse models of peripheral neuropathy. Knockout mice were used to study EBP50 function in the peripheral nervous system. Interestingly motor function deficit and abnormal histology of nerve fibers were observed in EBP50 heterozygous mice at 12 months of age, but not 3 months. in vitro studies using Schwann cells showed that NRG1-induced AKT activation and migration were significantly reduced in cells overexpressing the I325V mutant of EBP50 or cells with knocked-down EBP50 expression. In conclusion, we show for the first time that loss of function due to EBP50 gene deficiency or mutation can cause peripheral neuropathy.
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http://dx.doi.org/10.1002/glia.23805DOI Listing
September 2020

Behind the pathology of macrophage-associated demyelination in inflammatory neuropathies: demyelinating Schwann cells.

Cell Mol Life Sci 2020 Jul 28;77(13):2497-2506. Epub 2019 Dec 28.

Peripheral Neuropathy Research Center (PNRC), Dong-A University College of Medicine, Busan, 49201, South Korea.

In inflammatory peripheral demyelinating disorders, demyelination represents segmental demyelination in which the myelin sheath of a myelinating Schwann cell (SC) is completely removed by macrophages or a partial myelin degeneration in the paranode occurring due to autoantibodies attacking the node/paranode. For the segmental demyelination from living myelin-forming SCs, macrophages infiltrate within the endoneurium and insinuate between myelin lamellae and the cytoplasm of SCs, and the myelin is then removed via phagocytosis. During the macrophage invasion into the SC cytoplasm from the node of Ranvier and internodal areas, the attacked SCs do not remain quiescent but transdifferentiate into inflammatory demyelinating SCs (iDSCs), which exhibit unique demyelination pathologies, such as myelin uncompaction from Schmidt-Lanterman incisures with myelin lamellae degeneration. The longitudinal extension of this self-myelin clearance process of iDSCs into the nodal region is associated with the degeneration of nodal microvilli and paranodal loops, which provides a potential locus for macrophage infiltration. In addition to the nodal intrusion, macrophages appear to be able to invade fenestrated internodal plasma membrane or the degenerated outer mesaxon of iDSC. These SC demyelination morphologies indicate that the SC reprogramming to iDSCs may be a prerequisite for macrophage-mediated inflammatory demyelination. In contrast, paranodal demyelination caused by autoantibodies to nodal/paranodal antigens does not result in iDSC-dependent macrophage infiltration and subsequent segmental demyelination. In the context of inflammatory demyelination, the novel perspective of iDSCs provides an important viewpoint to understand the pathophysiology of demyelinating peripheral neuropathies and establish diagnostic and therapeutic strategies.
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http://dx.doi.org/10.1007/s00018-019-03431-8DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7320037PMC
July 2020

Differential expression of circular RNAs in the proximal and distal segments of the sciatic nerve after injury.

Neuroreport 2020 01;31(1):76-84

Peripheral Neuropathy Research Center, Department of Molecular Neuroscience, College of Medicine, Dong-A University, Busan, South Korea.

To investigate the functions of circular RNAs (circRNAs) in axonal regeneration and degeneration after injury, circRNA expression profiles in the injured peripheral nerves were determined using a circRNA-based microarray. The results showed that 281 upregulated and 261 downregulated circRNAs were found in the proximal stump of the sciatic nerve after injury. In the distal stump after injury, 217 circRNAs were upregulated and 224 circRNAs were downregulated. The Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment and gene ontology (GO) analysis of circRNAs after injury were associated with axon regeneration pathways, including thyroid hormone, Ras signaling, endocytosis, and the ErbB signaling pathway, as well as with Schwann cell differentiation and proliferation, including the axon guidance, focal adhesion, Glutamatergic synapse, and MAPK signaling pathway. To verify the microarray results, among the regulated circRNAs, the upregulation of circRNA 012142 in both proximal and distal segments was validated using quantitative PCR analysis. The biological function of the circRNA 012412/microRNA/mRNA network based on GO analysis and KEGG pathway was identified in cell differentiation, phosphorylation, intracellular signaling transduction, and focal adhesion, the Rap1 signaling pathway. Thus, circRNAs after nerve injury may be involved in these biological functions during nerve regeneration and degeneration.
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http://dx.doi.org/10.1097/WNR.0000000000001371DOI Listing
January 2020

Serum CXCL13 reflects local B-cell mediated inflammatory demyelinating peripheral neuropathy.

Sci Rep 2019 11 11;9(1):16535. Epub 2019 Nov 11.

Peripheral Neuropathy Research Center (PNRC), Dong-A University College of Medicine, Busan, 49201, Republic of Korea.

Immune damages on the peripheral myelin sheath under pro-inflammatory milieu result in primary demyelination in inflammatory demyelinating neuropathy. Inflammatory cytokines implicating in the pathogenesis of inflammatory demyelinating neuropathy have been used for the development of potential biomarkers for the diagnosis of the diseases. In this study, we have found that macrophages, which induce demyelination, expressed a B-cell-recruiting factor CXC chemokine ligand 13 (CXCL13) in mouse and human inflammatory demyelinating nerves. The serum levels of CXCL13 were also higher in inflammatory demyelinating neuropathic patients but not in acute motor axonal neuropathy or a hereditary demyelinating neuropathy, Charcot-Marie-Tooth disease type 1a. In addition, CXCL13-expressing macrophages were not observed in the sciatic nerves after axonal injury, which causes the activation of innate immunity and Wallerian demyelination. Our findings indicate that the detection of serum CXCL13 will be useful to specifically recognize inflammatory demyelinating neuropathies in human.
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http://dx.doi.org/10.1038/s41598-019-52643-2DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6848485PMC
November 2019

Heat Shock Protein 90 is Required for cAMP-Induced Differentiation in Rat Primary Schwann Cells.

Neurochem Res 2019 Nov 12;44(11):2643-2657. Epub 2019 Oct 12.

Department of Biochemistry, Dong-A University College of Medicine, 32, Daesingongwon-ro, Seo-Gu, Busan, 49201, Republic of Korea.

Schwann cells (SCs) play an important role in producing myelin for rapid neurotransmission in the peripheral nervous system. Activation of the differentiation and myelination processes in SCs requires the expression of a series of transcriptional factors including Sox10, Oct6/Pou3f1, and Egr2/Krox20. However, functional interactions among several transcription factors are poorly defined and the important components of the regulatory network are still unknown. Until now, available evidence suggests that SCs require cAMP signaling to initiate the myelination program. Heat shock protein 90 (Hsp90) is known as a chaperone required to stabilize ErbB2 receptor. In recent years, it was reported that cAMP transactivated the ErbB2/ErbB3 signaling in SCs. However, the relationship between Hsp90 and cAMP-induced differentiation in SCs is undefined. Here we investigated the role of Hsp90 during cAMP-induced differentiation of SCs using Hsp90 inhibitor, geldanamycin and Hsp90 siRNA transfection. Our results showed that dibutyryl-cAMP (db-cAMP) treatment upregulated Hsp90 expression and led to nuclear translocation of Gab1/ERK, the downstream signaling pathway of the ErbB2 signaling mechanism in myelination. The expression of myelin-related genes and nuclear translocation of Gab1/ERK following db-cAMP treatment was inhibited by geldanamycin pretreatment and Hsp90 knockdown. These findings suggest that Hsp90 might play a role in cAMP-induced differentiation via stabilization of ErbB2 and nuclear translocation of Gab1/ERK in SCs.
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http://dx.doi.org/10.1007/s11064-019-02885-3DOI Listing
November 2019

Downregulation MIWI-piRNA regulates the migration of Schwann cells in peripheral nerve injury.

Biochem Biophys Res Commun 2019 11 17;519(3):605-612. Epub 2019 Sep 17.

Peripheral Neuropathy Research Center, Department of Molecular Neuroscience, College of Medicine, Dong-A University, Dongdaesin-Dong, Seo-Gu, Busan, 602-714, South Korea.

Although MIWI (PIWI in humans) regulates spermatogenesis and translation machinery, its role in peripheral nerve injury is poorly understood. In this study, we characterized the expression profiles of MIWI after sciatic nerve injury. The results revealed that MIWI was downregulated after sciatic nerve injury. MIWI was colocalized with S100 (a Schwan cell marker), and TOM20 (a mitochondrial marker) on uncut nerves, while some MIWI was also colocalized with myelin protein zero (a myelin marker) on injured nerves. Immunofluorescence revealed that some MIWI was colocalized with SOX10 in the nuclear compartment following nerve injury. MIWI depletion by MIWI siRNA resulted in the reduction of EGR2. To characterize the expression of PIWI interacting RNA (piRNA) during sciatic nerve injury, microarray-based piRNA was conducted. The results revealed that 3447 piRNAs were upregulated, while 4117 piRNAs were downregulated after nerve transection. Interestingly, piR 009614 downregulated the mRNA level of MBP and enhanced the migration of RT-4 Schwann cells. Together, our results suggest that the MIWI-piRNA complex may play a role in Schwann cell responses to nerve injury.
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http://dx.doi.org/10.1016/j.bbrc.2019.09.008DOI Listing
November 2019

p75 and neural cell adhesion molecule 1 can identify pathologic Schwann cells in peripheral neuropathies.

Ann Clin Transl Neurol 2019 07 2;6(7):1292-1301. Epub 2019 Jul 2.

Peripheral Neuropathy Research Center (PNRC), Dong-A University College of Medicine, Busan, 49201, Republic of Korea.

Objective: Myelinated Schwann cells (SCs) in adult peripheral nerves dedifferentiate into immature cells in demyelinating neuropathies and Wallerian degeneration. This plastic SC change is actively involved in the myelin destruction and clearance as demyelinating SCs (DSCs). In inherited demyelinating neuropathy, pathologically differentiated and dysmyelinated SCs constitute the main nerve pathology.

Methods: We investigated whether this SC plastic status in human neuropathic nerves could be determined by patient sera to develop disease-relevant serum biomarkers. Based on proteomics analysis of the secreted exosomes from immature SCs, we traced p75 neurotrophin receptor (p75) and neural cell adhesion molecule 1 (NCAM) in the sera of patients with peripheral neuropathy.

Results: Enzyme-linked immunosorbent assay (ELISA) revealed that p75 and NCAM were subtype-specifically expressed in the sera of patients with peripheral neuropathy. In conjunction with these ELISA data, pathological analyses of animal models and human specimens suggested that the presence of DSCs in inflammatory neuropathy and of supernumerary nonmyelinating or dysmyelinating SCs in inherited neuropathy could potentially be distinguished by comparing the expression profiles of p75 and NCAM.

Interpretation: This study indicates that the identification of disease-specific pathological SC stages might be a valuable tool for differential diagnosis of peripheral neuropathies.
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http://dx.doi.org/10.1002/acn3.50828DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6649441PMC
July 2019

Pattern of Extraocular Muscle Involvements in Miller Fisher Syndrome.

J Clin Neurol 2019 Jul;15(3):308-312

Department of Neurology, Dong-A University College of Medicine, Busan, Korea.

Background And Purpose: The most-common initial manifestation of Miller Fisher syndrome (MFS) is diplopia due to acute ophthalmoplegia. However, few studies have focused on ocular motility findings in MFS. This study aimed to determine the pattern of extraocular muscle (EOM) paresis in MFS patients.

Methods: We consecutively recruited MFS patients who presented with ophthalmoplegia between 2010 and 2015. The involved EOMs and the strabismus pattern in the primary position were analyzed. Antecedent infections, other involved cranial nerves, and laboratory findings were also reviewed. We compared the characteristics of the patients according to the severity of ophthalmoplegia between complete ophthalmoplegia (CO) and incomplete ophthalmoplegia (IO).

Results: Twenty-five patients (15 males and 10 females) with bilateral ophthalmoplegia were included in the study. The most-involved and last-to-recover EOM was the lateral rectus muscle. CO and IO were observed in 11 and 14 patients, respectively. The patients were aged 59.0±18.4 years (mean±SD) in the CO group and 24.9±7.4 years in the IO group (<0.01), and comprised 63.6% and 21.4% females, respectively (=0.049). Elevated cerebrospinal fluid protein was identified in 60.0% of patients with CO and 7.7% of patients with IO (=0.019) for a mean follow-up time from the initial symptom onset of 3.7 days.

Conclusions: The lateral rectus muscle is the most-involved and last-to-recover EOM in ophthalmoplegia. The CO patients were much older and were more likely to be female and have an elevation of cerebrospinal fluid protein than the IO patients.
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http://dx.doi.org/10.3988/jcn.2019.15.3.308DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6620438PMC
July 2019

miR-381 Attenuates Peripheral Neuropathic Phenotype Caused by Overexpression of PMP22.

Exp Neurobiol 2019 Apr 30;28(2):279-288. Epub 2019 Apr 30.

Department of Biochemistry, College of Medicine, Dong-A University, Busan 49201, Korea.

Charcot-Marie Tooth disease type 1A (CMT1A), the major type of CMT, is caused by duplication of peripheral myelin protein 22 () gene whose overexpression causes structural and functional abnormalities in myelination. We investigated whether miRNA-mediated regulation of PMP22 expression could reduce the expression level of PMP22, thereby alleviating the demyelinating neuropathic phenotype of CMT1A. We found that several miRNAs were down-regulated in C22 mouse, a CMT1A mouse model. Among them, miR-381 could target 3' untranslated region (3'UTR) of in vitro based on Western botting and quantitative Real Time-PCR (qRT-PCR) results. In vivo efficacy of miR-381 was assessed by administration of LV-miR-381, an miR-381 expressing lentiviral vector, into the sciatic nerve of C22 mice by a single injection at postnatal day 6 (p6). Administration of LV-miR-381 reduced expression level of PMP22 along with elevated level of miR-381 in the sciatic nerve. Rotarod performance analysis revealed that locomotor coordination of LV-miR-381 administered C22 mice was significantly enhanced from 8 weeks post administration. Electrophysiologically, increased motor nerve conduction velocity was observed in treated mice. Histologically, toluidine blue staining and electron microscopy revealed that structural abnormalities of myelination were improved in sciatic nerves of LV-miR-381 treated mice. Therefore, delivery of miR-381 ameliorated the phenotype of peripheral neuropathy in CMT1A mouse model by down-regulating expression. These data suggest that miRNA can be used as a potent therapeutic strategy to control diseases with copy number variations such as CMT1A.
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http://dx.doi.org/10.5607/en.2019.28.2.279DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6526106PMC
April 2019

Assessment of mitophagy in mt-Keima revealed an essential role of the PINK1-Parkin pathway in mitophagy induction .

FASEB J 2019 09 23;33(9):9742-9751. Epub 2019 May 23.

Peripheral Neuropathy Research Center, College of Medicine, Dong-A University, Busan, Korea.

Mitophagy has been implicated in mitochondrial quality control and in various human diseases. However, the study of mitophagy remains limited. We previously explored mitophagy using a transgenic mouse expressing the mitochondria-targeted fluorescent protein Keima (mt-Keima). Here, we generated mt-Keima to extend our efforts to study mitophagy . A series of experiments confirmed that mitophagy can be faithfully and quantitatively measured in mt-Keima . We also showed that alterations in mitophagy upon environmental and genetic perturbation can be measured in mt-Keima . Analysis of different tissues revealed a variation in basal mitophagy levels in tissues. In addition, we found a significant increase in mitophagy levels during embryogenesis. Importantly, loss-of-function genetic analysis demonstrated that the phosphatase and tensin homolog-induced putative kinase 1 (PINK1)-Parkin pathway is essential for the induction of mitophagy in response to hypoxic exposure and rotenone treatment. These studies showed that the mt-Keima system is a useful tool for understanding the role and molecular mechanism of mitophagy . In addition, we demonstrated the essential role of the PINK1-Parkin pathway in mitophagy induction in response to mitochondrial dysfunction.-Kim, Y. Y., Um, J.-H., Yoon, J.-H., Kim, H., Lee, D.-Y., Lee, Y. J., Jee, H. J., Kim, Y. M., Jang, J. S., Jang, Y.-G., Chung, J., Park, H. T., Finkel, T., Koh, H., Yun, J. Assessment of mitophagy in mt-Keima revealed an essential role of the PINK1-Parkin pathway in mitophagy induction .
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http://dx.doi.org/10.1096/fj.201900073RDOI Listing
September 2019

Aminosalicylic acid reduces ER stress and Schwann cell death induced by MPZ mutations.

Int J Mol Med 2019 Jul 2;44(1):125-134. Epub 2019 May 2.

Department of Biochemistry, College of Medicine, Dong‑A University, Busan 49201, Republic of Korea.

Mutations in myelin protein zero (MPZ) cause inherited peripheral neuropathies, including Charcot‑Marie‑Tooth disease (CMT) and Dejerine‑Sottas neuropathy. Mutant MPZ proteins have previously been reported to cause CMT via enhanced endoplasmic reticulum (ER) stress and Schwann cell (SC) death, although the pathological mechanisms have not yet been elucidated. In this study, we generated an in vitro model of rat SCs expressing mutant MPZ (MPZ V169fs or R98C) proteins and validated the increase in cell death and ER stress induced by the overexpression of the MPZ mutants. Using this model, we examined the efficacy of 3 different aminosalicylic acids (ASAs; 4‑ASA, sodium 4‑ASA and 5‑ASA) in alleviating pathological phenotypes. FACS analysis indicated that the number of apoptotic rat SCs, RT4 cells, induced by mutant MPZ overexpression was significantly reduced following treatment with each ASA. In particular, treatment with 4‑ASA reduced the levels of ER stress markers in RT4 cells induced by V169fs MPZ mutant overexpression and relieved the retention of V169fs mutant proteins in the ER. Additionally, the level of an apoptotic signal mediator (p‑JNK) was only decreased in the RT4 cells expressing R98C MPZ mutant protein following treatment with 4‑ASA. Although 4‑ASA is known as a free radical scavenger, treatment with 4‑ASA in the in vitro model did not moderate the level of reactive oxygen species, which was elevated by the expression of mutant MPZ proteins. On the whole, the findings of this study indicate that treatment with 4‑ASA reduced the ER stress and SC death caused by 2 different MPZ mutants and suggest that ASA may be a potential therapeutic agent for CMT.
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http://dx.doi.org/10.3892/ijmm.2019.4178DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6559330PMC
July 2019

Drp1 Phosphorylation Is Indispensable for Steroidogenesis in Leydig Cells.

Endocrinology 2019 04;160(4):729-743

Department of Anatomy and Cell Biology, College of Medicine, Dong-A University, Busan, Republic of Korea.

The initial steps of steroidogenesis occur in the mitochondria. Dynamic changes in the mitochondria are associated with their fission and fusion. Therefore, understanding the cellular and molecular relationships between steroidogenesis and mitochondrial dynamics is important. The hypothesis of the current study is that mitochondrial fission and fusion are closely associated with steroid hormone synthesis in testicular Leydig cells. Steroid hormone production, induced by dibutyryl cAMP (dbcAMP) in Leydig cells, was accompanied by increased mitochondrial mass. Mitochondrial elongation increased during the dbcAMP-induced steroid production, whereas mitochondrial fragmentation was reduced. Among the mitochondrial-shaping proteins, the level of dynamin-associated protein 1 (Drp1) was altered in response to dbcAMP stimulation. The increase in Drp1 Ser 637 phosphorylation correlated with steroid hormone production in the MA-10 Leydig cells as well as in the primary adult rat Leydig cells. Drp1 was differentially expressed in the Leydig cells during testicular development. Finally, gonadotropin administration altered the status of Drp1 phosphorylation in the Leydig cells of immature rat testes. Overall, mitochondrial dynamics is directly linked to steroidogenesis, and Drp1 plays an important regulatory role during steroidogenesis. This study shows that Drp1 level is regulated by cAMP and that its phosphorylation via protein kinase A (PKA) activation plays a decisive role in mitochondrial shaping by offering an optimal environment for steroid hormone biosynthesis in Leydig cells. Therefore, it is suggested that PKA-mediated Drp1 Ser 637 phosphorylation is indispensable for steroidogenesis in the Leydig cells, and this phosphorylation results in mitochondrial elongation via the relative attenuation of mitochondrial fission during steroidogenesis.
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http://dx.doi.org/10.1210/en.2019-00029DOI Listing
April 2019

Activation of the Nrf2/HO-1 signaling pathway contributes to the protective effects of baicalein against oxidative stress-induced DNA damage and apoptosis in HEI193 Schwann cells.

Int J Med Sci 2019 1;16(1):145-155. Epub 2019 Jan 1.

Anti-Aging Research Center and Department of Biochemistry, Dongeui University College of Korean Medicine, Busan 47227, Republic of Korea.

Baicalein, a flavonoid extracted from the roots of Georgi., has various pharmacological effects due to its high antioxidant activity. However, no study has yet been conducted on the protective efficacy of baicalein against oxidative stress in Schwann cells. In this study, we evaluated the protective effect of baicalein on DNA damage and apoptosis induced by hydrogen peroxide (HO) in HEI193 Schwann cells. For this purpose, HEI193 cells exposed to HO in the presence or absence of baicalein were applied to cell viability assay, immunoblotting, Nrf2-specific small interfering RNA (siRNA) transfection, comet assay, and flow cytometry analyses. Our results showed that baicalein effectively inhibited HO-induced cytotoxicity and DNA damage associated with the inhibition of reactive oxygen species (ROS) accumulation. Baicalein also weakened HO-induced mitochondrial dysfunction, increased the Bax/Bcl-2 ratio, activated caspase-9 and -3, and degraded poly(ADP-ribose) polymerase. In addition, baicalein increased not only the expression but also the phosphorylation of nuclear factor-erythroid 2 related factor 2 (Nrf2) and promoted the expression of heme oxygenase-1 (HO-1), a critical target enzyme of Nrf2, although the expression of kelch-like ECH-associated protein-1 was decreased. However, the inhibition of Nrf2 expression by transfection with Nrf2-siRNA transfection abolished the expression of HO-1 and antioxidant potential of baicalein. These results demonstrate that baicalein attenuated HO-induced apoptosis through the conservation of mitochondrial function while eliminating ROS in HEI193 Schwann cells, and the antioxidant efficacy of baicalein implies at least a Nrf2/HO-1 signaling pathway-dependent mechanism. Therefore, it is suggested that baicalein may have a beneficial effect on the prevention and treatment of peripheral neuropathy induced by oxidative stress.
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http://dx.doi.org/10.7150/ijms.27005DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6332480PMC
April 2019

Protective Effect of Baicalein on Oxidative Stress-induced DNA Damage and Apoptosis in RT4-D6P2T Schwann Cells.

Int J Med Sci 2019 1;16(1):8-16. Epub 2019 Jan 1.

Anti-Aging Research Center, Dong-eui University, Busan 47340, Republic of Korea.

Due to its high antioxidant activity, baicalein, a kind of flavonoid present in Radical Scutellariae, has various pharmacological effects. However, the protective effect against oxidative stress in Schwann cells, which plays an important role in peripheral neuropathy, has not yet been studied. In this study, the effects of baicalein on hydrogen peroxide (HO)-induced DNA damage and apoptosis in RT4-D6P2T Schwann cells were evaluated. Cell viability assay was performed using MTT assay and colony formation assay. Apoptosis was assessed by flow cytometry analysis and DNA fragmentation assay. The effects on DNA damage and ATP content were analyzed by comet method and luminometer. In addition, changes in protein expression were observed by Western blotting. Our results show that baicalein significantly inhibits HO-induced cytotoxicity through blocking reactive oxygen species (ROS) generation. We also demonstrate that baicalein is to block HO-induced DNA damage as evidenced by inhibition of DNA tail formation and γH2AX phosphorylation. Moreover, baicalein significantly attenuated HO-induced apoptosis and mitochondrial dysfunction, and restored inhibition of ATP production. The suppression of apoptosis by baicalein in HO-stimulated cells was associated with reduction of increased Bax/Bcl-2 ratio, activation of caspase-9 and -3, and degradation of poly (ADP-ribose) polymerase. These results demonstrate that baicalein eliminates HO-induced apoptosis through conservation of mitochondrial function by the removal of ROS. Therefore, it is suggested that baicalein protects Schwann cells from oxidative stress, and may be beneficial for the prevention and treatment of peripheral neuropathy induced by oxidative stress.
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http://dx.doi.org/10.7150/ijms.29692DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6332490PMC
April 2019

A Variant Identified in a Sporadic Amyotrophic Lateral Sclerosis Patient Impairs Microtubule Stability and Axonal Mitochondria Distribution.

Exp Neurobiol 2018 Dec 12;27(6):550-563. Epub 2018 Dec 12.

Department of Brain and Cognitive Sciences and Dental Research Institute, Seoul National University, Seoul 08826, Korea.

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease that is frequently linked to microtubule abnormalities and mitochondrial trafficking defects. Whole exome sequencing (WES) of patient-parent trios has proven to be an efficient strategy for identifying rare genetic variants responsible for sporadic ALS (sALS). Using a trio-WES approach, we identified a variant (c.4069G>A, p.E1357K) in a patient with early-onset sALS. To assess the pathogenic effects of this variant, we have used patient-derived skin fibroblasts and motor neuron-specific overexpression of the RAPGEF2-E1357K mutant protein in . Patient fibroblasts display reduced microtubule stability and defective microtubule network morphology. The intracellular distribution, ultrastructure, and function of mitochondria are also impaired in patient cells. Overexpression of the RAPGEF2 mutant in motor neurons reduces the stability of axonal microtubules and disrupts the distribution of mitochondria to distal axons and neuromuscular junction (NMJ) synapses. We also show that the recruitment of the pro-apoptotic protein BCL2-associated X (BAX) to mitochondria is significantly increased in patient fibroblasts compared with control cells. Finally, increasing microtubule stability through pharmacological inhibition of histone deacetylase 6 (HDAC6) rescues defects in the intracellular distribution of mitochondria and BAX. Overall, our data suggest that the variant identified in this study can drive ALS-related pathogenic effects through microtubule dysregulation.
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http://dx.doi.org/10.5607/en.2018.27.6.550DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6318558PMC
December 2018

MicroRNAs 93-5p, 106b-5p, 17-5p, and 140-5p target the expression of early growth response protein 2 in Schwann cells.

Neuroreport 2019 02;30(3):241-246

Department of Molecular Neuroscience, Peripheral Neuropathy Research Center, College of Medicine, Dong-A University, Busan, South Korea.

Early growth response protein 2 (EGR2) is an essential transcription factor for peripheral nerve myelination. Schwann cells (SCs), the peripheral myelin-forming glial cells, express high levels of EGR2 during postnatal myelination. In contrast, SCs exhibit low EGR2 expression during Wallerian degeneration after injury. In this study, we screened 10 potential microRNAs (miRNAs) (20a-5p, 137-5p, 140-5p, 148b-3p, 150-5p, 17-5p, 93-5p, 20b-5p, 106b-5p, and 152-3p) that potentially target EGR2 using miRNA algorithms and identified that miRNAs 106b-5p, 140-5p, 93-5p, and 17-5p target EGR2 in SCs. These miRNAs directly target EGR2 by binding to the 3'-untranslated region to suppress EGR2 mRNA levels. Additionally, the levels of miRNAs 93-5p, 106b-5p, 17-5p, and 140-5p were decreased in the sciatic nerves during postnatal development; however, these miRNAs were increased on day 1 after sciatic nerve injury. Taken together, these findings suggest that the expression of EGR2 during postnatal development and Wallerian degeneration could be regulated by the inverse expression of miRNAs 106b-5p, 140-5p, 93-5p, and 17-5p, which target EGR2.
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http://dx.doi.org/10.1097/WNR.0000000000001193DOI Listing
February 2019

Upregulation of microRNA 344a-3p is involved in curcumin induced apoptosis in RT4 schwannoma cells.

Cancer Cell Int 2018 4;18:199. Epub 2018 Dec 4.

Peripheral Neuropathy Research Center, Department of Molecular Neuroscience, College of Medicine, Dong-A University, Dongdaesin-Dong, Seo-Gu, Busan, 602-714 South Korea.

Background: Schwannoma arising from peripheral nervous sheaths is a benign tumor.

Methods: To evaluate cell cytotoxicity, (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) tetrazolium reduction and terminal deoxynucleotidyltransferase UTP nick-end labeling (TUNEL) assays were used. A microRNA (miRNA) array was used to identify the miRNAs involved in curcumin-induced apoptosis. To examine miRNA expression, quantitative RT-PCR was used.

Results: In this study, curcumin exerted cellular cytotoxicity against RT4 schwannoma cells, with an increase in TUNEL-positive cells. Curcumin also activated the expression of apoptotic proteins, such as polyADP ribose polymerase, caspase-3, and caspase-9. The miRNA array revealed that seven miRNAs (miRNA 350, miRNA 17-2-3p, let 7e-3p, miRNA1224, miRNA 466b-1-3p, miRNA 18a-5p, and miRNA 322-5p) were downregulated following treatment with both 10 and 20 μM curcumin in RT4 cells, while four miRNAs (miRNA122-5p, miRNA 3473, miRNA182, and miRNA344a-3p) were upregulated. Interestingly, transfection with a miRNA 344a-3p mimic downregulated the mRNA expression of Bcl2 and upregulated that of Bax, Curcumin treatment in RT 4 cells also reduced the mRNA expression of Bcl2 and enhanced expression of Bax, Overexpression of miRNA344a-3p mimic combined with curcumin treatment activated the expression of apoptotic proteins, including procaspase-9 and cleaved caspase-3 while inhibition of miRNA 344a-3p using miR344a-3p inhibitor repressed cleaved caspase-3 and -9 in curcumin treated RT-4 cells compared to control.

Conclusions: Our findings demonstrate that curcumin induces apoptosis in schwannoma cells via miRNA 344a-3p. Thus, curcumin may serve as a potent therapeutic agent for the treatment of schwannoma.
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http://dx.doi.org/10.1186/s12935-018-0693-xDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6278133PMC
December 2018

Isorhamnetin alleviates lipopolysaccharide-induced inflammatory responses in BV2 microglia by inactivating NF-κB, blocking the TLR4 pathway and reducing ROS generation.

Int J Mol Med 2019 Feb 20;43(2):682-692. Epub 2018 Nov 20.

Department of Biochemistry, Dongeui University College of Korean Medicine, Busan 47227, Republic of Korea.

Isorhamnetin, which is a flavonoid predominantly found in fruits and leaves of various plants, including Hippophae rhamnoides L. and Oenanthe javanica (Blume) DC, is known to possess various pharmacological effects. However, the anti‑inflammatory potential of isorhamnetin remains poorly studied. Therefore, the present study aimed to investigate the inhibitory potential of isorhamnetin against inflammatory responses in lipopolysaccharide (LPS)‑stimulated BV2 microglia. To measure the effects of isorhamnetin on inflammatory mediators and cytokines, and reactive oxygen species (ROS) generation, the following methods were used: cell viability assay, griess assay, ELISA, reverse transcriptase‑polymerase chain reaction, flow cytometry, western blotting and immunofluorescence staining. The results revealed that isorhamnetin significantly suppressed LPS‑induced secretion of pro‑inflammatory mediators, including nitric oxide (NO) and prostaglandin E2, without exhibiting significant cytotoxicity. Consistent with these results, isorhamnetin inhibited LPS‑stimulated expression of regulatory enzymes, including inducible NO synthase and cyclooxygenase‑2 in BV2 cells. Isorhamnetin also downregulated LPS‑induced production and expression of pro‑inflammatory cytokines, such as tumor necrosis factor‑α and interleukin‑1β. The mechanism underlying the anti‑inflammatory effects of isorhamnetin was subsequently evaluated; this flavonoid inhibited the nuclear factor (NF)‑κB signaling pathway by disrupting degradation and phosphorylation of inhibitor κB‑α in the cytoplasm and blocking translocation of NF‑κB p65 into the nucleus. In addition, isorhamnetin effectively suppressed LPS‑induced expression of Toll‑like receptor 4 (TLR4) and myeloid differentiation factor 88. It also suppressed the binding of LPS with TLR4 in BV2 cells. Furthermore, isorhamnetin markedly reduced LPS‑induced generation of ROS in BV2 cells, thus indicating a strong antioxidative effect. Collectively, these results suggested that isorhamnetin may suppress LPS‑mediated inflammatory action in BV2 microglia through inactivating the NF‑κB signaling pathway, antagonizing TLR4 and eliminating ROS accumulation. Further studies are required to fully understand the anti‑inflammatory effects associated with the antioxidant capacity of isorhamnetin; however, the findings of the present study suggested that isorhamnetin may have potential benefits in inhibiting the onset and treatment of neuroinflammatory diseases.
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http://dx.doi.org/10.3892/ijmm.2018.3993DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6317673PMC
February 2019

The conceptual introduction of the "demyelinating Schwann cell" in peripheral demyelinating neuropathies.

Glia 2019 04 30;67(4):571-581. Epub 2018 Oct 30.

INSERM U1051, Institut des Neurosciences de Montpellier (INM), Université de Montpellier, Montpellier, France.

Myelinating Schwann cells undergo irreversible demyelination in many demyelinating neuropathies that show complete demyelination of the internode. Dedifferentiation, reprogramming, and myelin clearance processes-which are specifically discussed in this article-appear to be shared by various demyelinating peripheral conditions, such as Wallerian degeneration, immune-mediated, and toxic demyelinating diseases. We propose to introduce the concept of the "demyelinating Schwann cell (DSC)" as a novel cell phenotype, which has specific properties required for myelin sheath clearance. We anticipate that the introduction of the DSC concept will provide a significant advance in understanding the pathophysiological mechanisms of demyelinating peripheral neuropathies.
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http://dx.doi.org/10.1002/glia.23509DOI Listing
April 2019

Palmitate induces lipoapoptosis in Schwann cells through ROS generation-mediated STAMP2 downregulation.

Biochem Biophys Res Commun 2018 09 11;503(3):1260-1266. Epub 2018 Jul 11.

Department of Anatomy and Cell Biology, Dong-A University College of Medicine and Mitochondria Hub Regulation Center, 3-1 Dongdaesin-Dong, Seo-Gu, Busan, Republic of Korea. Electronic address:

Free fatty acids (FFAs) are considered the principal inducers of lipotoxicity, leading to cell dysfunction and/or cell death. Lipotoxicity in Schwann cells (SCs) damages neurons, which may be associated with peripheral neuropathies and axon degeneration. However, the molecular mechanism by which FFAs exert lipotoxicity in SCs remains to be established. In the present study, we demonstrate that palmitate exerts lipotoxicity in SCs through apoptosis and that palmitate-induced lipotoxicity in SCs is mediated through reactive oxygen species (ROS) generation. We observed that the six-transmembrane protein of prostate 2 (STAMP2), which plays a pivotal role in lipid homeostasis, is expressed in SCs. We further demonstrate that palmitate induces lipoapoptosis in SCs through ROS generation-mediated STAMP2 downregulation and that STAMP2 depletion accelerates the palmitate-exerted lipoapoptosis in SCs, indicating that STAMP2 confers on SCs the ability to resist palmitate-induced lipotoxicity. In conclusion, palmitate induces lipoapoptosis in SCs through ROS generation-mediated STAMP2 downregulation. Our findings indicate that ROS and STAMP2 may represent suitable targets for pharmacological interventions targeting lipotoxicity-associated peripheral neuropathies and axon degeneration.
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http://dx.doi.org/10.1016/j.bbrc.2018.07.034DOI Listing
September 2018

MicroRNA Mediated Regulation of Schwann Cell Migration and Proliferation in Peripheral Nerve Injury.

Biomed Res Int 2018 30;2018:8198365. Epub 2018 Apr 30.

Peripheral Neuropathy Research Center, Department of Physiology, College of Medicine, Dong-A University, Busan, Republic of Korea.

Schwann cells (SCs) contribute to nerve repair following injury; however, the underlying molecular mechanism is poorly understood. MicroRNAs (miRNAs), which are short noncoding RNAs, have been shown to play a role in neuronal disease. In this work, we show that miRNAs regulate the peripheral nerve system by modulating the migration and proliferation of SCs. Thus, miRNAs expressed in peripheral nerves may provide a potential therapeutic target for peripheral nerve injury or repair.
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http://dx.doi.org/10.1155/2018/8198365DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5952561PMC
October 2018

Natural agents mediated autophagic signal networks in cancer.

Cancer Cell Int 2017 28;17:110. Epub 2017 Nov 28.

Peripheral Neuropathy Research Center, Department of Physiology, College of Medicine, Dong-A University, Dongdaesin-Dong, Seo-Gu, Busan, 602-714 Republic of Korea.

Recent studies suggested that natural compounds are important in finding targets for cancer treatments. Autophagy ("self-eating") plays important roles in multiple diseases and acts as a tumor suppressor in cancer. Here, we examined the molecular mechanism by which natural agents regulate autophagic signals. Understanding the relationship between natural agents and cellular autophagy may provide more information for cancer diagnosis and chemoprevention.
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http://dx.doi.org/10.1186/s12935-017-0486-7DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5704453PMC
November 2017

Isocitrate protects DJ-1 null dopaminergic cells from oxidative stress through NADP+-dependent isocitrate dehydrogenase (IDH).

PLoS Genet 2017 Aug 21;13(8):e1006975. Epub 2017 Aug 21.

Department of Pharmacology, Peripheral Neuropathy Research Center (PNRC), Dong-A University College of Medicine, Busan, Republic of Korea.

DJ-1 is one of the causative genes for early onset familiar Parkinson's disease (PD) and is also considered to influence the pathogenesis of sporadic PD. DJ-1 has various physiological functions which converge on controlling intracellular reactive oxygen species (ROS) levels. In RNA-sequencing analyses searching for novel anti-oxidant genes downstream of DJ-1, a gene encoding NADP+-dependent isocitrate dehydrogenase (IDH), which converts isocitrate into α-ketoglutarate, was detected. Loss of IDH induced hyper-sensitivity to oxidative stress accompanying age-dependent mitochondrial defects and dopaminergic (DA) neuron degeneration in Drosophila, indicating its critical roles in maintaining mitochondrial integrity and DA neuron survival. Further genetic analysis suggested that DJ-1 controls IDH gene expression through nuclear factor-E2-related factor2 (Nrf2). Using Drosophila and mammalian DA models, we found that IDH suppresses intracellular and mitochondrial ROS level and subsequent DA neuron loss downstream of DJ-1. Consistently, trimethyl isocitrate (TIC), a cell permeable isocitrate, protected mammalian DJ-1 null DA cells from oxidative stress in an IDH-dependent manner. These results suggest that isocitrate and its derivatives are novel treatments for PD associated with DJ-1 dysfunction.
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http://dx.doi.org/10.1371/journal.pgen.1006975DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5578699PMC
August 2017

Schwann cell dedifferentiation-associated demyelination leads to exocytotic myelin clearance in inflammatory segmental demyelination.

Glia 2017 11 10;65(11):1848-1862. Epub 2017 Aug 10.

Department of Physiology, Peripheral Neuropathy Research Center, College of Medicine, Dong-A University, Busan, 49201, Republic of Korea.

Schwann cells (SCs), which form the peripheral myelin sheath, have the unique ability to dedifferentiate and to destroy the myelin sheath under various demyelination conditions. During SC dedifferentiation-associated demyelination (SAD) in Wallerian degeneration (WD) after axonal injury, SCs exhibit myelin and junctional instability, down-regulation of myelin gene expression and autophagic myelin breakdown. However, in inflammatory demyelinating neuropathy (IDN), it is still unclear how SCs react and contribute to segmental demyelination before myelin scavengers, macrophages, are activated for phagocytotic myelin digestion. Here, we compared the initial SC demyelination mechanism of IDN to that of WD using microarray and histochemical analyses and found that SCs in IDN exhibited several typical characteristics of SAD, including actin-associated E-cadherin destruction, without obvious axonal degeneration. However, autophagolysosome activation in SAD did not appear to be involved in direct myelin lipid digestion by SCs but was required for the separation of SC body from destabilized myelin sheath in IDN. Thus, lysosome inhibition in SCs suppressed segmental demyelination by preventing the exocytotic myelin clearance of SCs. In addition, we found that myelin rejection, which might also require the separation of SC cytoplasm from destabilized myelin sheath, was delayed in SC-specific Atg7 knockout mice in WD, suggesting that autophagolysosome-dependent exocytotic myelin clearance by SCs in IDN and WD is a shared mechanism. Finally, autophagolysosome activation in SAD was mechanistically dissociated with the junctional destruction in both IDN and WD. Thus, our findings indicate that SAD could be a common myelin clearance mechanism of SCs in various demyelinating conditions.
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http://dx.doi.org/10.1002/glia.23200DOI Listing
November 2017

Cooperative interaction of hepatocyte growth factor and neuregulin regulates Schwann cell migration and proliferation through Grb2-associated binder-2 in peripheral nerve repair.

Glia 2017 11 19;65(11):1794-1808. Epub 2017 Jul 19.

Department of Physiology, Peripheral Neuropathy Research Center (PNRC), College of Medicine, Dong-A University, Busan, South Korea.

The sequential reactive changes in Schwann cell phenotypes in transected peripheral nerves, including dedifferentiation, proliferation and migration, are essential for nerve repair. Even though the injury-induced migratory and proliferative behaviors of Schwann cells resemble epithelial and mesenchymal transition (EMT) in tumors, the molecular mechanisms underlying this phenotypic change of Schwann cells are still unclear. Here we show that the reactive Schwann cells exhibit migratory features dependent on the expression of a scaffolding oncoprotein Grb2-associated binder-2 (Gab2), which was transcriptionally induced by neuregulin 1-ErbB2 signaling following nerve injury. Injury-induced Gab2 expression was dependent on c-Jun, a transcription factor critical to a Schwann cell reprograming into a repair-type cell. Interestingly, the injury-induced activation (tyrosine phosphorylation) of Gab2 in Schwann cells was regulated by an EMT signal, the hepatocyte growth factor-c-Met signaling, but not by neuregulin 1. Gab2 knockout mice exhibited a deficit in nerve repair after nerve transection due to limited Schwann cell migration. Furthermore, Gab2 was required for the proliferation of Schwann cells following nerve injury and in vitro, and was over-expressed in human Schwann cell-derived tumors. In contrast, the tyrosine phosphorylation of Gab1 after nerve injury was principally regulated by the neuregulin 1-ErbB2 signaling and was indispensable for remyelination after crush injury, but not for the proliferation and migration of Schwann cells. Our findings indicate that Gab1 and Gab2 in Schwann cells are nonredundant and play a crucial role in peripheral nerve repair.
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http://dx.doi.org/10.1002/glia.23195DOI Listing
November 2017

The Scaffolding Protein, Grb2-associated Binder-1, in Skeletal Muscles and Terminal Schwann Cells Regulates Postnatal Neuromuscular Synapse Maturation.

Exp Neurobiol 2017 Jun 16;26(3):141-150. Epub 2017 Jun 16.

Department of Physiology, College of Medicine, Dong-A University, Busan 49201, Korea.

The vertebrate neuromuscular junction (NMJ) is considered as a "tripartite synapse" consisting of a motor axon terminal, a muscle endplate, and terminal Schwann cells that envelope the motor axon terminal. The neuregulin 1 (NRG1)-ErbB2 signaling pathway plays an important role in the development of the NMJ. We previously showed that Grb2-associated binder 1 (Gab1), a scaffolding mediator of receptor tyrosine kinase signaling, is required for NRG1-induced peripheral nerve myelination. Here, we determined the role of Gab1 in the development of the NMJ using muscle-specific conditional Gab1 knockout mice. The mutant mice showed delayed postnatal maturation of the NMJ. Furthermore, the selective loss of the gene in terminal Schwann cells produced delayed synaptic elimination with abnormal morphology of the motor endplate, suggesting that Gab1 in both muscles and terminal Schwann cells is required for proper NMJ development. Gab1 in terminal Schwann cells appeared to regulate the number and process elongation of terminal Schwann cells during synaptic elimination. However, Gab2 knockout mice did not show any defects in the development of the NMJ. Considering the role of Gab1 in postnatal peripheral nerve myelination, our findings suggest that Gab1 is a pleiotropic and important component of NRG1 signals during postnatal development of the peripheral neuromuscular system.
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http://dx.doi.org/10.5607/en.2017.26.3.141DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5491582PMC
June 2017