Hee-Yul Ahn

Chungbuk National University, Chinsen, North Chungcheong, South Korea

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Publications (10)23.79 Total impact

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    Chan-Hyung Kim · Jia Hao · Hee-Yul Ahn · Si Wook Kim
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    ABSTRACT: Akt/protein kinase B is a well-known cell survival factor and activated by many stimuli including mechanical stretching. Therefore, we evaluated the cardioprotective effect of a brief mechanical stretching of rat hearts and determined whether activation of Akt through phosphatidylinositol 3-kinase (PI3K) is involved in stretch-induced cardioprotection (SIC). Stretch preconditioning reduced infarct size and improved post-ischemic cardiac function compared to the control group. Phosphorylation of Akt and its downstream substrate, GSK-3β, was increased by mechanical stretching and completely blocked by wortmannin, a PI3K inhibitor. Treatment with lithium or SB216763 (GSK-3β inhibitors) before ischemia induction mimicked the protective effects of SIC on rat heart. Gadolinium (Gd3+), a blocker of stretch-activated ion channels (SACs), inhibited the stretch-induced phosphorylation of Akt and GSK-3β. Furthermore, SIC was abrogated by wortmannin and Gd3+. In vivo stretching induced by an aorto-caval shunt increased Akt phosphorylation and reduced myocardial infarction; these effects were diminished by wortmannin and Gd3+ pretreatment. Our results showed that mechanical stretching can provide cardioprotection against ischemia-reperfusion injury. Additionally, the activation of Akt, which might be regulated by SACs and the PI3K pathway, plays an important role in SIC.
    Journal of Veterinary Science 09/2012; 13(3):235. DOI:10.4142/jvs.2012.13.3.235 · 1.16 Impact Factor
  • Ji-Young Choi · Tae-Sun Ha · Hye-Young Park · Hee-Yul Ahn
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    ABSTRACT: Background: Adenosine monophosphate (AMP)-activated protein kinase (AMPK), as a sensor of cellular energy status, has been known to play an important role in the pathophysiology of diabetes and its complications. As AMPK is also expressed in podocytes, it is possible that podocyte AMPK would be an important contributing factor in the development of diabetic proteinuria. We investigated the roles of AMPK in the pathological changes of podocytes induced by angiotensin II (Ang II), a major injury inducer in diabetic proteinuria. Methods: Mouse podocytes were incubated in media containing various concentrations of Ang II and AMPK-modulating agents. The changes of AMPKα were analyzed by confocal imaging and Western blotting in response to Ang II. Results: Ang II changed the localization of AMPKα from peripheral cytoplasm into internal cytoplasm and peri- and intranuclear areas in podocytes. Ang II also reduced AMPKα (Thr172) phosphorylation in time- and dose-sensitive manners. In particular, 10(-7 )M Ang II reduced phospho-AMPKα significantly and continuously at 6, 24, and 48 h. AMPK activators, metformin and 5-aminoimidazole-4-carboxamide-1β-riboside, restored the suppressed AMPKα (Thr172) phosphorylation. Losartan, an Ang II type 1 receptor antagonist, also recovered the suppression and the mal-localization of AMPKα, which were induced by Ang II. PD98059, a mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) kinase (MEK) inhibitor, also restored the AMPKα (Thr172) phosphorylation suppressed by Ang II. Conclusion: We suggest that Ang II induces the relocation and suppression of podocyte AMPKα via Ang II type 1 receptor and MAPK signaling pathway, which would be an important mechanism in Ang II-induced podocyte injury.
    Clinical and Experimental Nephrology 06/2012; 17(1). DOI:10.1007/s10157-012-0649-8 · 2.02 Impact Factor
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    ABSTRACT: AMP-activated protein kinase (AMPK) protects various tissues and cells from ischemic insults and is activated by many stimuli including mechanical stretch. Therefore, this study investigated if the activation of AMPK is involved in stretch-induced cardioprotection (SIC). Intraventricular balloon and aorto-caval shunt (ACS) were used to stretch rat hearts ex vivo and in vivo, respectively. Stretch preconditioning reduced myocardial infarct induced by ischemia-reperfusion (I/R) and improved post-ischemic functional recovery. Phosphorylation of AMPK and its downstream substrate, acetyl-CoA carboxylase (ACC) were increased by mechanical stretch and ACC phosphorylation was completely blocked by the AMPK inhibitor, Compound C. AMPK activator (AICAR) mimicked SIC. Gadolinium, a blocker of stretch-activated ion channels (SACs), inhibited the stretch-induced phosphorylation of AMPK and ACC, whereas diltiazem, a specific L-type calcium channel blocker, did not affect AMPK activation. Furthermore, SIC was abrogated by Compound C and gadolinium. The in vivo stretch induced by ACS increased AMPK activation and reduced myocardial infarct. These findings indicate that stretch preconditioning can induce the cardioprotection against I/R injury, and activation of AMPK plays an important role in SIC, which might be mediated by SACs.
    Korean Journal of Physiology and Pharmacology 02/2010; 14(1):1-9. DOI:10.4196/kjpp.2010.14.1.1 · 1.38 Impact Factor
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    Tae-Sun Ha · Eun-Jeong Hong · Eun-Mi Ahn · Hee-Yul Ahn
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    ABSTRACT: An early feature of diabetic nephropathy is the alteration of the glomerular basement membrane (GBM), which may result in microalbuminuria, subsequent macroproteinuria, and eventual chronic renal failure. Although type IV collagen is the main component of thickened GBM in diabetic nephropathy, cellular metabolism of each alpha chains of type IV collagen has not been well studied. To investigate the regulation of alpha(IV) chains in diabetic conditions, we examined whether glucose and advanced glycosylation endproduct (AGE) regulate the metabolism of each alpha(IV) chains in the diabetic tissue and glomerular epithelial cells (GEpC). Glomerular collagen alpha3(IV) and alpha5(IV) chains protein were higher and more intense in immunofluorescence staining according to diabetic durations compared to controls. In vitro, mainly high glucose and partly AGE usually increased total collagen protein of GEpC by [(3)H]-proline incorporation assay and each alpha(IV) chain proteins including alpha1(IV), alpha3(IV), and alpha5(IV) in time-dependent and subchain-specific manners. However, the changes of each alpha(IV) chains mRNA expression was not well correlated to the those of each chain proteins. The present findings suggest that the metabolism of individual alpha(IV) chains of GBM is differentially regulated in diabetic conditions and those changes might be induced not only by transcriptional level but also by post-translational modifications.
    Journal of Korean medical science 10/2009; 24(5):837-43. DOI:10.3346/jkms.2009.24.5.837 · 1.27 Impact Factor
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    ABSTRACT: Inhibition of cardiac hypertrophy leads to a significant reduction in cardiovascular mortality and morbidity. Quercetin is by far the most abundant flavonoid and believed to ameliorate cardiovascular disease. Therefore, we investigated whether quercetin supplementation could attenuate the development of cardiac hypertrophy induced by pressure overload. Three weeks after suprarenal transverse abdominal aortic constriction, heart to body weight (HW/BW) ratio increased compared to the sham group (3.40 +/- 0.06 mg/g versus 2.83 +/- 0.02 mg/g, P<0.001). The quercetin administered group showed complete inhibition of cardiac hypertrophy (2.85 +/- 0.01 mg/g, P<0.001). Malonyldialdehyde production induced by pressure overload was suppressed by quercetin. The activities of extracellular signal-regulated kinase (ERK1/2), p38 MAP kinase, Akt and GSK-3beta were significantly increased with pressure overload and attenuated by quercetin treatment. We conclude that quercetin appears to block the development of cardiac hypertrophy induced by pressure overload in rats and that these effects may be mediated through reduced oxidant status and inhibition of ERK1/2, p38 MAP kinase, Akt and GSK-3beta activities.
    Journal of Veterinary Medical Science 07/2009; 71(6):737-43. DOI:10.1292/jvms.71.737 · 0.78 Impact Factor
  • Source
    Jia Hao · Chan-Hyung Kim · Tae-Sun Ha · Hee-Yul Ahn
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    ABSTRACT: Pressure overload diseases, such as valvular stenosis and systemic hypertension, manifest morphologically in patients as cardiac concentric hypertrophy. Prevention of cardiac remodeling due to increased pressure overload is important to reduce morbidity and mortality. Epigallocatechin-3 gallate (EGCG) is a major bioactive polyphenol present in green tea which has been found to be a nitric oxide-mediated vasorelaxant and to be cardioprotective in myocardial ischemia-reperfusion injury. Therefore, we investigated whether EGCG supplementation could reduce in vivo pressure overloadmediated cardiac hypertrophy. Cardiac hypertrophy was induced by suprarenal transverse abdominal aortic constriction (AC) in rats. Three weeks after AC surgery, heart to body weight ratio increased in the AC group by 34% compared to the sham group. EGCG administration suppressed the load-induced increase in heart weight by 69%. Attenuation of cardiac hypertrophy by EGCG was associated with attenuation of the increase in myocyte cell size and fibrosis induced by aortic constriction. Despite abolition of hypertrophy by EGCG, transstenotic pressure gradients did not change. Echocardiogram revealed that increased left ventricular systolic dimensions and deteriorated systolic function were relieved by EGCG. These results suggest that EGCG prevents the development of left ventricular concentric hypertrophy by pressure overload and may be a useful therapeutic modality to prevent cardiac remodeling in patients with pressure overload myocardial diseases.
    Journal of Veterinary Science 07/2007; 8(2):121-9. DOI:10.4142/jvs.2007.8.2.121 · 1.16 Impact Factor
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    ABSTRACT: It has been shown that green tea catechins (GTC) suppress proliferation of vascular smooth muscle cells (VSMCs) and that epigallocatechin-3-gallate (EGCG), which is a major constituent of GTC, selectively inhibits the platelet-derived growth factor-BB (PDGF-BB)-induced intracellular signaling transduction pathway. Vascular smooth muscle cell proliferation is one of major mechanisms of restenosis following percutaneous coronary intervention. This study tested whether GTC can inhibit VSMC proliferation and prevent neointimal formation in a rat carotid artery injury model. Vascular smooth muscle cell proliferation inhibition was analyzed with [3H]thymidine incorporation. Green tea catechins were applied to the endothelium-denuded carotid arteries of rats for 20 min. Angiography and morphometric analysis was performed after 2 weeks. Green tea catechins decreased [3H]thymidine incorporation stimulated with PDGF-BB dose dependently. In the absence of PDGF-BB, the decrement of [3H]thymidine incorporation was evident above a concentration of 10 micro g/ml of GTC. Carotid arteriographic evaluation showed that the minimum luminal diameter in the GTC-treated group (n=12) was 5.9 +/- 1.6 arbitrary units (a.u.) and was significantly larger than in the control group (4.3 +/- 1.4 a.u., n=10) ( P <0.05). The GTC-treated group also showed a significant reduction in neointimal formation compared with the control group (0.29 +/- 0.11 vs 0.42 +/- 0.10 mm2, P < 0.05). To identify the active ingredients, we performed a similar experiment using EGCG. The effects of EGCG were similar to those of GTC. Green tea catechins effectively inhibited VSMC proliferation. Neointimal formation was prevented in the rat carotid artery injury model by local delivery of GTC. As EGCG showed similar effects, it may be one of the major constituents of GTC having these effects.
    Heart and Vessels 09/2004; 19(5):242-7. DOI:10.1007/s00380-004-0768-6 · 2.07 Impact Factor
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    ABSTRACT: An enhanced activity of receptor tyrosine kinases (RTKs), such as the platelet-derived growth factor (PDGF) alpha-receptor (PDGF-Ralpha) or the PDGF beta-receptor (PDGF-Rbeta), is involved in the development of proliferative diseases. We have previously demonstrated that green tea catechins containing a galloyl group in the third position of the catechin structure interfere with PDGF-BB-induced mitogenic signaling pathways by inhibiting tyrosine phosphorylation of the PDGF-Rbeta. However, the underlying cellular and molecular mechanisms are unknown. Using human vascular smooth muscle cells (VSMC) and porcine endothelial cells (AEC) stably transfected with PDGF-Ralpha and -beta, respectively, we demonstrate that EGCG preferably inhibited PDGF-BB isoform-mediated signal transduction pathways and cell proliferation. To elucidate cellular and molecular mechanisms of the inhibitory effects of EGCG, we studied the distribution of incorporated EGCG into cellular compartments after subcellular fractionation. Interestingly, most (85%) of the EGCG was found in the cytoplasmic fraction, whereas only ~2% was found within the cell plasma membranes. However, no alteration of membrane fluidity has been observed after treatment of VSMC with 50 microM EGCG. Binding studies with [125I]-PDGF-BB on EGCG-treated VSMC demonstrated that the specific binding of PDGF-BB was completely abolished. Moreover, when [125I]-PDGF-BB was incubated with VSMC in the presence of EGCG, a 50% reduction of cellular [125I]-PDGF-BB binding was observed. Our findings suggest that plasma membrane incorporated EGCG or soluble EGCG directly interacts with PDGF-BB, thereby preventing specific receptor binding.
    The FASEB Journal 02/2004; 18(1):128-30. DOI:10.1096/fj.03-0007fje · 5.04 Impact Factor
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    ABSTRACT: Abnormal proliferation of vascular smooth muscle cells (VSMC) as well as the platelet-derived growth factor (PDGF) plays an important role in the development of proliferative cardiovascular diseases. In this study, we show that treatment of rat and human aortic VSMC with 50 microM 2-(3,4-dihydroxyphenyl)-3,4-dihydro-2H-1-benzopyran-3,5,7-triol (catechin) and epicatechin (EC) fails to inhibit the PDGF-Rb-activated intracellular signal transduction pathway and VSMC growth. In contrast, 10-50 microM epigallocatechin-3 gallate (EGCG), epicatechin-3 gallate (ECG), and catechin-3 gallate (CG), which all have a galloyl group in the 3-position of the catechin structure, effectively inhibit tyrosine-phosphorylation of PDGF-Rb, PI 3'-K, and PLC-gamma1 as well as the PDGF-BB-induced increase in [Ca2+]i. The PDGF-BB-induced increase in DNA synthesis and cell number was inhibited by ECG, EGCG, and CG, but not by catechin and EC. Epigallocatechin (EGC) that has a galloyl group in the 2-position effectively inhibited VSMC growth without affecting the PDGF-Rb signal pathway. A reduction of 45% and 70% of the intimal and medial cell number in the S-phase, respectively, has been observed in the catheter-injured left carotid artery 7 days after treatment of Wistar Kyoto rats with 10 mg/day EGCG. These results suggest that the galloyl group in the P3-position of the catechin structure is essential for inhibiting the PDGF-Rbeta-mediated intracellular signal transduction pathway.
    The FASEB Journal 07/2002; 16(8):893-5. DOI:10.1096/fj.01-0799fje · 5.04 Impact Factor
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    ABSTRACT: The effect of the green tea compounds 2-(3,4-dihydroxyphenyl)-3, 4-dihydro-2H-1-benzopyran-3,5,7-triol (catechin), epicathechin (EC), epigallocathechin-3 gallate (EGCG), epicathechin-3 gallate (ECG) and catechin-3 gallate (CG) on the tyrosine phosphorylation of PDGF beta-receptor (PDGF-Rbeta) and on the anchorage-independent growth of A172 glioblastoma cells in semisolid agar has been investigated. Treatment of A172 glioblastoma with 50 microM CG, ECG, EGCG and 25 microM Tyrphostin 1296 resulted in an 82+/-17%, 77+/-21%, 75+/-8% and 55+/-11%, respectively (mean+/-S.D., n=3) inhibition of the PDGF-BB-induced tyrosine phosphorylation of PDGF-Rbeta. The PDGF-Rbeta downstream intracellular transduction pathway including tyrosine phosphorylation of phospholipase C-gamma1 (PLC-gamma1) and phosphatidylinositol 3'-kinase (PI 3'-K) was also inhibited. Spheroid formation was completely inhibited by 50 microM ECG, CG, EGCG and by 25 microM Tyrphostin 1296. We conclude that catechins of the green tea possessing the gallate group in their chemical structure act as anticancer agents probably partly via their ability to suppress the tyrosine kinase activity of the PDGF-Rbeta.
    FEBS Letters 05/2000; 471(1):51-5. DOI:10.1016/S0014-5793(00)01360-0 · 3.17 Impact Factor

Publication Stats

248 Citations
23.79 Total Impact Points


  • 2004–2012
    • Chungbuk National University
      • • College of Medicine
      • • Department of Medicine
      • • Department of Pediatrics
      Chinsen, North Chungcheong, South Korea
  • 2000
    • University of Bonn
      • Medizinische Klinik und Poliklinik II
      Bonn, North Rhine-Westphalia, Germany