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Hyo-Eun Kim, Sung-E Choi, Soo-Jin Lee, Ji-Hyun Lee, Youn-Jung Lee, Sang Sun Kang, Jaesun Chun and Yup Kang

The present study was undertaken to determine how tumour necrosis factor-α (TNF-α) elicits the inhibition of glucose-stimulated insulin secretion (GSIS) in rat insulinoma cells (INS)-1 β-cells. TNF-α pretreatment did not change the expression levels of insulin, PDX-1, glucose transporter 2, glucokinase, KATP channels, Ca2 + channels, and exocytotic molecules and, furthermore, did not reduce the glucose-stimulated ATP level. On the other hand, TNF-α reduced the glucose-stimulated influx of Ca2 +. The TNF-α treatment was thought to activate c-Jun N-terminal kinase (JNK), p38 mitogen-activated protein kinase (MAPK), and NF-κB inflammatory signals, since TNF-α increased phospho-JNK and phospho-p38 and reduced IκB levels. Inhibitors of these signaling pathways prevented the TNF-α-induced reduction of the Ca2 + influx and GSIS. Overexpression of MEKK3, a possible mediator from the TNF-α receptor to the JNK/p38 and NK-κB signaling cascade, increased the levels of phospho-JNK, phospho-p38, and NF-κB, and reduced the glucose-stimulated Ca2 + influx and GSIS. The reduction of the Ca2 + influx and GSIS in MEKK3-overexpressing INS-1 cells was also prevented by inhibitors of JNK, p38, and NF-κB. These data demonstrate that TNF-α inhibits GSIS by reducing the glucose-stimulated Ca2 + influx, possibly through the activation of JNK and p38 MAPK and NF-κB inflammatory signals. Thus, our findings suggest that the activation of stress and inflammatory signals can contribute to the inhibition of GSIS in the development of diabetes.

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Eun Soo Lee, Mi-Hye Kwon, Hong Min Kim, Nami Kim, You Mi Kim, Hyeon Soo Kim, Eun Young Lee and Choon Hee Chung

Dibenzoylmethane (DBM) is a beta-diketone analog of curcumin. Numerous studies have shown the beneficial effects of curcumin on diabetes, obesity and diabetic complications including diabetic nephropathy. Recently, we investigated the beneficial metabolic effects of DBM on high-fat diet-induced obesity. However, the effects and mechanisms of action of DBM in the kidney are currently unknown. To investigate the renoprotective effects of DBM in type 2 diabetes, we administered DBM (100 mg/kg) orally for 12 weeks to high-fat diet-induced diabetic model mice. We used mouse renal mesangial (MES13) and macrophage (RAW 264.7) cells to examine the mechanism of action of DBM (20 μM). After DBM treatment, the albumin-to-creatinine ratio was significantly decreased compared to that of the high-fat-diet group. Moreover, damaged renal ultra-structures and functions including increased glomerular volume, glomerular basement membrane thickness and inflammatory signals were ameliorated after DBM treatment. Stimulation of MES13 and RAW264.7 cells by palmitate or high-dose glucose with lipopolysaccharides increased inflammatory signals and macrophage migration. However, these changes were reversed by DBM treatment. In addition, DBM inhibited NADPH oxidase 2 and 4 expression and oxidative DNA damage. Collectively, these data suggested that DBM prevented diabetes-induced renal injury through its anti-inflammatory and antioxidant effects.

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Eun-Jin Kang, So-Hye Hong, Jae-Eon Lee, Seung Chul Kim, Hoe-Saeng Yang, Pyong in Yi, Sang-Myeong Lee and Beum-Soo An

Pregnenolone sulfate (PS) is a neuroactive steroid hormone produced in the brain. In this study, the effects of PS on synthesis and secretion of rat pituitary prolactin (PRL) were examined. To accomplish this, GH3 rat pituitary adenoma cells were treated with PS, which showed significantly increased mRNA and protein levels of PRL compared with the control. The mechanism of action responsible for the effects of PS on PRL synthesis and secretion was investigated by pretreating cells with inhibitors of traditional PRL- or the PS-related signaling pathway. PS-stimulated PRL transcription was significantly reduced by inhibitors of PKA, PKC and MAPK, but unchanged by GABAAR and NMDAR inhibitors. Western blotting analysis revealed that the total ERK1/2 level was upregulated in a time-dependent manner following PS treatment. An approximate 10% increase in GH3 cell proliferation was also observed in response to PS relative to the control. In the animal study, levels of PRL in the pituitary and in serum were elevated by PS. PS-stimulated PRL synthesis was also found to be associated with decreased expression of PRL target genes such as GNRH1, FSHB and LHB. These findings show that PS upregulates PRL synthesis and secretion in vivo and in vitro via MAPK signaling, suggesting that it has the potential for use as a therapeutic hormone to treat PRL-related disorders such as hypoprolactinemia and low milk supply.

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Mi Ae Cho, Mi Kyung Lee, Kee-Hyun Nam, Woung Youn Chung, Cheong Soo Park, Ju Hyeong Lee, Taewoong Noh, Woo Ick Yang, Yumie Rhee, Sung-Kil Lim, Hyun Chul Lee and Eun Jig Lee

Medullary thyroid carcinoma (MTC) originates from parafollicular C cells. Estrogen receptor β(ERβ) expressionwas detected in normal parafollicular C cells and MTC tumor tissue, but ERα expression in MTC tumors still remains undetermined. The appearance and loss of ERα or ERβ expression has been known to play a role in the development and progression of many human cancers. We performed immunohistochemical studies of ERα, ERβ, and Ki67, a mitotic index, in 11 human MTC tissue samples. ERα was detected in 10 cases (91%), and ERβ expression was observed in 8 cases (72.7%). A majority (8/10) of ERα-positive tumors showing ERβ Ki67 expression was detected in three cases (27.3%). Neither clinical parameters nor tumor node metastasis (TNM) tumor staging was correlated with the positivity for ERs or Ki67. To investigate the biological role of each ER, we used ER-negative MTC TT cells and adenoviral vectors carrying ERα (Ad-ERα), ERβ (Ad-ERβ), estrogen response element (ERE)-Luc (Ad-ERE-Luc), and activator protein 1 (AP1)-Luc (Ad-AP1-Luc). Estrogen stimulated and anti-estrogen, ICI 182 780, suppressed ERE reporter activity in TT cells expressing ERα or ERβ, suggesting that both ERs use the same classical ERE-mediated pathway. Ad-ERα infection stimulated TT cell growth; in contrast, Ad-ERβ infection suppressed their growth. Apoptosis was detected in Ad-ERβ-infected TT cells. Estrogen and anti-estrogen suppressed AP1 activity in Ad-ERα-infected cells, whereas upon Ad-ERβ infection estrogen further stimulated AP1 activity which in turn is suppressed by anti-estrogen, suggesting that each ER acts differently through a non-ERE-mediated pathway. Our results suggest that ERα and ERβ may play different roles in MTC tumor growth and progression.

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Yeon-Ju Lee, Se-Hui Jung, JongYun Hwang, Sohee Jeon, Eun-Taek Han, Won Sun Park, Seok-Ho Hong, Young-Myeong Kim and Kwon-Soo Ha

Cysteamine (an aminothiol), which is derived from coenzyme A degradation and metabolized into taurine, has beneficial effects against cystinosis and neurodegenerative diseases; however, its role in diabetic complications is unknown. Thus, we sought to determine the preventive effect of cysteamine against hyperglycemia-induced vascular leakage in the retinas of diabetic mice. Cysteamine and ethanolamine, the sulfhydryl group-free cysteamine analogue, inhibited vascular endothelial growth factor (VEGF)-induced stress fiber formation and vascular endothelial (VE)-cadherin disruption in endothelial cells, which play a critical role in modulating endothelial permeability. Intravitreal injection of the amine compounds prevented hyperglycemia-induced vascular leakage in the retinas of streptozotocin-induced diabetic mice. We then investigated the potential roles of reactive oxygen species (ROS) and transglutaminase (TGase) in the cysteamine prevention of VEGF-induced vascular leakage. Cysteamine, but not ethanolamine, inhibited VEGF-induced ROS generation in endothelial cells and diabetic retinas. In contrast, VEGF-induced TGase activation was prevented by both cysteamine and ethanolamine. Our findings suggest that cysteamine protects against vascular leakage through inhibiting VEGF-induced TGase activation rather than ROS generation in diabetic retinas.

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Mahendra Prasad Bhatt, Yeon-Ju Lee, Se-Hui Jung, Yong Ho Kim, Jong Yun Hwang, Eun-Taek Han, Won Sun Park, Seok-Ho Hong, Young-Myeong Kim and Kwon-Soo Ha

C-peptide exerts protective effects against diabetic complications; however, its role in inhibiting hyperglycemic memory (HGM) has not been elucidated. We investigated the beneficial effect of C-peptide on HGM-induced vascular damage in vitro and in vivo using human umbilical vein endothelial cells and diabetic mice. HGM induced apoptosis by persistent generation of intracellular ROS and sustained formation of ONOO and nitrotyrosine. These HGM-induced intracellular events were normalized by treatment with C-peptide, but not insulin, in endothelial cells. C-peptide also inhibited persistent upregulation of p53 and activation of mitochondrial adaptor p66shc after glucose normalization. Further, C-peptide replacement therapy prevented persistent generation of ROS and ONOO in the aorta of diabetic mice whose glucose levels were normalized by the administration of insulin. C-peptide, but not insulin, also prevented HGM-induced endothelial apoptosis in the murine diabetic aorta. This study highlights a promising role for C-peptide in preventing HGM-induced intracellular events and diabetic vascular damage.