Hyockman Kwon

Tunable Heptamethine–Azo Dye Conjugate as an NIR Fluorescent Probe for the Selective Detection of Mitochondrial Glutathione over Cysteine and Homocysteine

Although a lot of mitochondria-targeting biothiol probes have been developed and applied to cellular imaging through thiol-induced disulfide cleavage or Michael addition reactions, relatively few probes assess mitochondrial GSH with high selectivity over Cys and Hcy and with NIR fluorescence capable of noninvasive imaging in biological samples. In order to monitor mitochondrial GSH with low background autofluorescence, we designed a heptamethine-azo conjugate as an NIR fluorescent probe by introducing a tunable lipophilic cation unit as the biomarker for mitochondria and a nitroazo group as the GSH-selective reaction site as well as the fluorescence quencher. The probe exhibited a dramatic off-on NIR fluorescence response toward GSH with high selectivity over other amino acids including Cys and Hcy. Further application to cellular imaging indicated that the probe was highly responsive to the changes of mitochondrial GSH in cells.

Ratiometric Fluorescence Imaging of Cellular Glutathione

A fluorescent probe (1) with a hydrogen bond was designed for the detection of GSH. The probe exhibited a rapid and ratiometric fluorescence response to GSH through a Michael reaction and allowed us to obtain clear cellular images for GSH.

Neuregulin Stimulates Myogenic Differentiation in an Autocrine Manner

During myogenesis, mononucleated myoblasts form multinucleated myotubes by membrane fusion. Efficiency of this intercellular process can be maximized by a simultaneous progress, with a time window, of other neighboring myoblasts in the differentiation program. This phenomenon has been described as the community effect. It proposes the existence of a molecule that acts as a differentiation-inducing signal to a group of identical cells. Here ,we show that neuregulin is a strong candidate for this molecule in myoblast differentiation. The expression of neuregulin increased rapidly but transiently at early stage of differentiation of rat L6 cells. Neuregulin showed a potent differentiation-promoting activity in membrane fusion and expression of myosin heavy chain. The antibodies raised against neuregulin and its cognate receptor ErbB3, which were capable of neutralizing the signal pathway, inhibited myotube formation and expression of myosin heavy chain in both L6 cells and primary rat myoblasts. The progress of differentiation was mostly halted after the expression of myogenin and cell cycle arrest. These results suggest that the activation of an autocrine signaling of neuregulin may provide a basic mechanism for the community effect observed in the differentiation of the embryonic muscle cells.

Effects of Polygala tenuifolia root extract on proliferation of neural stem cells in the hippocampal CA1 region

Neurogenesis persists in the adult mammalian brain and can be a target for modulation for therapeutic purposes. This study investigated the effect of a Polygala tenuifolia root extract on the proliferation of a stem cell population in the rat hippocampus. The root extract of P. tenuifolia (2 mg/kg/day, 14 times intraperitoneal injections) increased the incorporation of bromodeoxyuridine (BrdU) into cells in the hippocampal CA1 region. This activity was enriched in the saponin‐containing fraction. The majority of cells labelled with BrdU were immunoreactive to nestin or Tuj1 and the percentages of nestin/BrdU‐ and Tuj1/BrdU‐double positive cells were increased by the P. tenuifolia root extract, suggesting that the P. tenuifolia root extract promotes the proliferation of neural stem cells. In addition, this extract promoted the neurite outgrowth of rat neuronal precursor cells, HiB5. These activities of P. tenuifolia root extract may contribute to the therapeutic benefits of herbal medicines containing P. tenuifolia root for the treatment of patients with insomnia, neurosis and dementia. Copyright

OPPOSITE EFFECT OF INTRACELLULAR CA2+ AND PROTEIN KINASE C ON THE EXPRESSION OF INWARDLY RECTIFYING K+ CHANNEL 1 IN MOUSE SKELETAL MUSCLE

The level of inwardly rectifying K+ channel 1 (IRK1) mRNA decreased upon denervation and increased during muscle differentiation in mouse skeletal muscle. To identify the mechanism(s) underlying the regulation of IRK1 mRNA expression, we examined its expression using the well differentiated C2C12 mouse skeletal muscle cell line as a model system. Since nerve-induced muscle activity results in contraction, it was questioned whether the changes in IRK1 expression might be relevant to the increased intracellular calcium that functions as a cytoplasmic messenger in excitation-contraction coupling. Indeed, activation of either l-type calcium channels or ryanodine receptors increased the level of IRK1 mRNA. More directly, ionomycin activated the IRK1 expression in time- and dose-dependent manners, which was abolished by treatment with EGTA. Genistein, a tyrosine kinase inhibitor, also abolished the stimulating effect of ionomycin. Meanwhile, activation of protein kinase C by 12-O-tetradecanoylphorbol acetate (TPA) markedly decreased the level of IRK1 mRNA, which required ongoing protein synthesis. Actinomycin D experiments revealed that ionomycin increased the half-life of IRK1 mRNA from 0.86 to 1.97 h, but TPA decreased it to 0.38 h. However, neither ionomycin nor TPA appreciably altered the rate of IRK1 gene transcription. Based on these observations, we conclude that intracellular calcium and protein kinase C are oppositely involved in the muscle activity-dependent regulation of IRK1 gene expression and that both act at the level of mRNA stability.

Ratiometric fluorescence probes based on a Michael acceptor type of coumarin and their application for the multichannel imaging of in vivo glutathione

A series of Michael acceptors based on a coumarin moiety, were developed as fluorescent probes for ratiometric detection of in vivo glutathione. The α,β-unsaturated Michael acceptors were transformed into non-conjugated molecules through the Michael addition of biothiols. The resulting UV-vis and fluorescence spectra of the probes revealed characteristic ratiometric responses, which were successfully applied for the multichannel imaging of in vivo glutathione.

Neuroprotective effects of berberine in neurodegeneration model rats induced by ibotenic acid

Abstract Berberine, an isoquinoline alkaloid found in Coptidis Rhizoma (goldenthread) extract, has multiple pharmacological effects such as anti‐inflammatory, antimicrobial and anti‐ischemic effects. In the present study, we examined the effects of berberine on neuronal survival and differentiation in a hippocampal precursor cell line and in the memory deficient rat model. Berberine increased in a dose dependent manner the survival of hippocampal precursor cells as well as differentiated cells. In addition, berberine promoted neuronal differentiation of hippocampal precursor cells. In the memory deficient rat model induced by stereotaxic injection of ibotenic acid into entorhinal cortex (Ibo model), hippocampal cells were increased about 2.7 fold in the pyramidal layer of CA1 region and about 2 fold in the dentate gyrus by administration of berberine after 2 weeks of ibotenic acid injection. Furthermore, neuronal cells immunoreactive to calbindin were increased in the hippocampus and entorhinal cortex area by administration of berberine. Taken together, these results suggest that berberine has neuroprotective effect in the Ibo model rat brain by promoting the neuronal survival and differentiation.

A fluoresceinylcarbonate-based fluorescent probe for the sensitive detection of biothiols in a HEPES buffer and its cellular expression

A fluoresceinylcarbonate-based fluorescent probe (1) with a disulfide bond was designed for the detection of biothiols in an aqueous solvent. The probe showed a more rapid and sensitive response to biothiols than other various amino acids through the disulfide bond cleavage and the subsequent intramolecular cyclization. When glutathione was added to the probe, fluorescence of 1 was significantly enhanced and was observable with the naked eye and in living cells.

Cycloserine-induced encephalopathy: evidence on brain MRI

Cycloserine is a structural analogue of the amino acid D-alanine commonly used as an anti-tuberculosis antibiotic. The nervous system is a frequent target of its adverse effects, which include drowsiness, dizziness, headache, lethargy, depression, tremor, dysarthria, hyperreflexia, paraesthesia, anxiety, confusion, seizure and coma [1]. However, this neurotoxicity has not been confirmed by neuroimaging studies. We report the recent experience of a case potentially related to the toxicity of cycloserine.

Upregulation of amyloid precursor protein by platelet-derived growth factor in hippocampal precursor cells.

Amyloid precursor protein generates the secreted amyloid precursor protein &agr;, which protects hippocampal neurons from ischemic injury and facilitates neuronal survival and synaptogenesis in the developing nervous system. Here, we examined whether platelet-derived growth factor regulates the generation of secreted amyloid precursor protein &agr; during the neuronal differentiation of hippocampal precursor cells, HiB5. We showed that platelet-derived growth factor promoted amyloid precursor protein production and secreted amyloid precursor protein &agr; secretion. These effects of platelet-derived growth factor were diminished by the PI3K-specific inhibitor wortmannin and the protein kinase C-specific inhibitor GF109203X, suggesting the involvement of the PI3K and protein kinase C-signaling pathway. Furthermore, the conditioned media enriched with secreted amyloid precursor protein &agr; promoted the survival of HiB5 cells during neuronal differentiation. These results suggest that the neurotrophic effect of platelet-derived growth factor is mediated in part via upregulation of the expression and release of secreted amyloid precursor protein &agr;.