Hyun Jin Tae

RAGE and cardiovascular disease.

RAGE is pattern recognizing receptors for diverse endogenous ligands. RAGE activation by RAGE ligands is known to be associated with reactive oxygen species generation, activation of NF kappa B, as well as recruitment of proinflammatory cells. Activated endothelial cells, vascular smooth muscle cells in atherosclerotic plaques and activated inflammatory cells all have increased expression of RAGE, which with its interaction with RAGE ligands increases the secretion of proinflammatory cytokines and cell adhesion molecules. Furthermore, RAGE may have a significant role in leukocyte recruitment into the intima of the atherosclerosis. Initial insults resulting in endothelial dysfunction will result in leukocyte infiltration, oxidative stress and vascular inflammation that is amplified by RAGE activation. RAGE and its interaction with RAGE ligands may be important for initializing and maintaining the pathological processes that result in various entities of cardiovascular disease. Soluble RAGE competitively inhibits the binding of RAGE ligands to RAGE and attenuates the development of atherosclerosis in vivo. Thus RAGE may be a promising target for treatment of cardiovascular disease in the future.

Effects of calorie restriction on cardioprotection and cardiovascular health.

Multiple health benefits of calorie restriction (CR) and alternate day fasting (ADF) regimens are widely recognized. Experimental data concerning the effects of calorie restriction on cardiac health are more controversial, ranging from evidence that ADF protects heart from ischemic damage but results in developing of diastolic dysfunction, to reports that CR ameliorates the age-associated diastolic dysfunction. Here we investigated the effects of chronic CR on morphology and function of the cardiovascular system of aged rats and cardioprotective effect of CR against ischemic damage in the experimental rat model of MI. Cardiovascular fitness of 24-month old Fisher 344 rats maintained through life on ad libitum (AL) or CR diets was extensively evaluated via echocardiography, dobutamine stress test, pressure-volume loop analyses, pulse wave velocity measurements, and histology. Groups of 2-month old AL and 29-month old CR rats were studied for comparison. Myocardial infarction (MI) was induced by a permanent ligation of the anterior descending coronary artery in 5-month old rats maintained for 3 months on CR or AL. MI size was evaluated histologically 24 hrs following coronary ligation. Cardiac remodeling was followed-up via echocardiography. Age-associated changes in 24-month old rats consisted of 33% increase of fibrosis in the myocardium and more than 2 fold increase of the collagen in the tunica media of the aorta. There was a significant decrease in the density and total number of cardiomyocytes, while their size was increased. These morphological changes were manifested in a decline of systolic and diastolic cardiac function, increase of left ventricular and aortic stiffness, and arterio-ventricular uncoupling. Tachycardic response to dobutamine challenge was absent in the old rats. Compared to AL rats, 24-month old CR rats had reduced levels of cardiac and aortic fibrosis, increased density of cardiomyocytes that were smaller in size, attenuated diastolic dysfunction, normal systolic function and arterio-ventricular coupling. Tachycardic response to dobutamine was also intact in CR 24-month old rats and aortic stiffness was reduced. Adjustment for body weight differences through ratiometric or allometric scaling did not affect the overall pattern of differences between AL and CR rats. Attenuation of morphological and functional age-associated changes in 24-month old CR rats either was not observed at all or was smaller in 29-month old CR rats. Size of MI induced by a permanent coronary ligation as well as post-MI cardiac remodeling and function were similar in CR and AL rats. CR does not increase tolerance of myocardium to ischemic damage, but attenuates the age-associated changes in the heart and major vessels. The attenuation of age-associated changes by CR cannot be explained by the effect of lower body weight but are attributable to more intimate cellular mechanisms of CR itself. Attenuation of age-associated changes by CR waned with advancing age, and is consistent with the idea that CR postponed senescence.

A small nonerythropoietic helix B surface peptide based upon erythropoietin structure is cardioprotective against ischemic myocardial damage.

Strong cardioprotective properties of erythropoietin (EPO) reported over the last 10 years have been difficult to translate to clinical applications for ischemic cardioprotection owing to undesirable parallel activation of erythropoiesis and thrombogenesis. A pyroglutamate helix B surface peptide (pHBP), recently engineered to include only a part of the EPO molecule that does not bind to EPO receptor and thus, is not erythropoietic, retains tissue protective properties of EPO. Here we compared the ability of pHBP and EPO to protect cardiac myocytes from oxidative stress in vitro and cardiac tissue from ischemic damage in vivo. HBP, similar to EPO, increased the reactive oxygen species (ROS) threshold for induction of the mitochondrial permeability transition by 40%. In an experimental model of myocardial infarction induced by permanent ligation of a coronary artery in rats, a single bolus injection of 60 µg/kg of pHBP immediately after coronary ligation, similar to EPO, reduced apoptosis in the myocardial area at risk, examined 24 h later, by 80% and inflammation by 34%. Myocardial infarction (MI) measured 24 h after coronary ligation was similarly reduced by 50% in both pHBP- and EPO-treated rats. Two wks after surgery, left ventricular remodeling (ventricular dilation) and functional decline (fall in ejection fraction) assessed by echocardiography were significantly and similarly attenuated in pHBP- and EPO-treated rats, and MI size was reduced by 25%. The effect was retained during the 6-wk follow-up. A single bolus injection of pHBP immediately after coronary ligation was effective in reduction of MI size in a dose as low as 1 µg/kg, but was ineffective at a 60 µg/kg dose if administered 24 h after MI induction. We conclude that pHBP is equally cardioprotective with EPO and deserves further consideration as a safer alternative to rhEPO in the search for therapeutic options to reduce myocardial damage following blockade of the coronary circulation.

Chronic Administration of Small Nonerythropoietic Peptide Sequence of Erythropoietin Effectively Ameliorates the Progression of Postmyocardial Infarction–Dilated Cardiomyopathy

The cardioprotective properties of erythropoietin (EPO) in preclinical studies are well documented, but erythropoietic and prothrombotic properties of EPO preclude its use in chronic heart failure (CHF). We tested the effect of long-term treatment with a small peptide sequence within the EPO molecule, helix B surface peptide (HBSP), that possesses tissue-protective, but not erythropoietic properties of EPO, on mortality and cardiac remodeling in postmyocardial infarction–dilated cardiomyopathy in rats. Starting 2 weeks after permanent left coronary artery ligation, rats received i.p. injections of HBSP (60 µg/kg) or saline two times per week for 10 months. Treatment did not elicit an immune response, and did not affect the hematocrit. Compared with untreated rats, HBSP treatment reduced mortality by 50% (P < 0.05). Repeated echocardiography demonstrated remarkable attenuation of left ventricular dilatation (end-diastolic volume: 41 versus 86%; end-systolic volume: 44 versus 135%; P < 0.05), left ventricle functional deterioration (ejection fraction: −4 versus −63%; P < 0.05), and myocardial infarction (MI) expansion (3 versus 38%; P < 0.05). A hemodynamic assessment at study termination demonstrated normal preload independent stroke work (63 ± 5 versus 40 ± 4; P < 0.05) and arterioventricular coupling (1.2 ± 0.2 versus 2.7 ± 0.7; P < 0.05). Histologic analysis revealed reduced apoptosis (P < 0.05) and fibrosis (P < 0.05), increased cardiomyocyte density (P < 0.05), and increased number of cardiomyocytes in myocardium among HBSP-treated rats. The results indicate that HBSP effectively reduces mortality, ameliorates the MI expansion and CHF progression, and preserves systolic reserve in the rat post-MI model. There is also a possibility that HBSP promoted the increase of the myocytes number in the myocardial wall remote from the infarct. Thus, HBSP peptide merits consideration for clinical testing.

Striated muscle tropomyosin isoforms differentially regulate cardiac performance and myofilament calcium sensitivity

Tropomyosin (TM) plays a central role in calcium mediated striated muscle contraction. There are three muscle TM isoforms: α-TM, β-TM, and γ-TM. α-TM is the predominant cardiac and skeletal muscle isoform. β-TM is expressed in skeletal and embryonic cardiac muscle. γ-TM is expressed in slow-twitch musculature, but is not found in the heart. Our previous work established that muscle TM isoforms confer different physiological properties to the cardiac sarcomere. To determine whether one of these isoforms is dominant in dictating its functional properties, we generated single and double transgenic mice expressing β-TM and/or γ-TM in the heart, in addition to the endogenously expressed α-TM. Results show significant TM protein expression in the βγ-DTG hearts: α-TM: 36%, β-TM: 32%, and γ-TM: 32%. These βγ-DTG mice do not develop pathological abnormalities; however, they exhibit a hyper contractile phenotype with decreased myofilament calcium sensitivity, similar to γ-TM transgenic hearts. Biophysical studies indicate that γ-TM is more rigid than either α-TM or β-TM. This is the first report showing that with approximately equivalent levels of expression within the same tissue, there is a functional dominance of γ-TM over α-TM or β-TM in regulating physiological performance of the striated muscle sarcomere. In addition to the effect expression of γ-TM has on Ca2+ activation of the cardiac myofilaments, our data demonstrates an effect on cooperative activation of the thin filament by strongly bound rigor cross-bridges. This is significant in relation to current ideas on the control mechanism of the steep relation between Ca2+ and tension.

Ghrelin augments murine T-cell proliferation by activation of the phosphatidylinositol-3-kinase, extracellular signal-regulated kinase and protein kinase C signaling pathways

Thymic atrophy occurs during normal aging, and is accelerated by exposure to chronic stressors that elevate glucocorticoid levels and impair the naïve T cell output. The orexigenic hormone ghrelin was recently shown to attenuate age‐associated thymic atrophy. Here, we report that ghrelin enhances the proliferation of murine CD4+ primary T cells and a CD4+ T‐cell line. Ghrelin induced activation of the ERK1/2 and Akt signaling pathways, via upstream activation of phosphatidylinositol‐3‐kinase and protein kinase C, to enhance T‐cell proliferation. Moreover, ghrelin induced expression of the cell cycle proteins cyclin D1, cyclin E, cyclin‐dependent kinase 2 (CDK2) and retinoblastoma phosphorylation. Finally, ghrelin activated the above‐mentioned signaling pathways and stimulated thymocyte proliferation in young and older mice in vivo.

Tellurium Compound AS101 Ameliorates Experimental Autoimmune Encephalomyelitis by VLA-4 Inhibition and Suppression of Monocyte and T Cell Infiltration into the CNS

Multiple sclerosis (MS) is an inflammatory autoimmune disease of the central nervous system (CNS) involving demyelinating and neurodegenerative processes. Several of the major pathological CNS alterations and behavioral deficits of MS are recapitulated in the experimental autoimmune encephalitis (EAE) mouse model in which the disease process is induced by administration of myelin peptides. Development of EAE requires infiltration of inflammatory cytokine-generating monocytes and macrophages, and auto-reactive T cells, into the CNS. Very late antigen-4 (VLA-4, α4β1) is an integrin molecule that plays a role in inflammatory responses by facilitating the migration of leukocytes across the blood–brain barrier during inflammatory disease, and antibodies against VLA-4 exhibit therapeutic efficacy in mouse and monkey MS models. Here, we report that the tellurium compound AS101 (ammonium trichloro (dioxoethylene-o,o′) tellurate) ameliorates EAE by inhibiting monocyte and T cell infiltration into the CNS. CD49d is an alpha subunit of the VLA-4 (α4β1) integrin. During the peak stage of EAE, AS101 treatment effectively ameliorated the disease process by reducing the number of CD49d+ inflammatory monocyte/macrophage cells in the spinal cord. AS101 treatment markedly reduced the pro-inflammatory cytokine levels, while increasing anti-inflammatory cytokine levels. In contrast, AS101 treatment did not affect the peripheral populations of CD11b+ monocytes and macrophages. AS101 treatment reduced the infiltration of CD4+ and CD49+/VLA4 T cells. In addition, treatment of T cells from MS patients with AS101 resulted in apoptosis, while such treatment did not affect T cells from healthy donors. These results suggest that AS101 reduces accumulation of leukocytes in the CNS by inhibiting the activity of the VLA-4 integrin and provide a rationale for the potential use of Tellurium IV compounds for the treatment of MS.

Long-term low dose dietary resveratrol supplement reduces cardiovascular structural and functional deterioration in chronic heart failure in rats

A short-term exposure to resveratrol at high dosages exerts a remarkable cardioprotective effect. Whether a long-term exposure to resveratrol at low dosages that can be obtained through consumption of a resveratrol-rich diet is beneficial to heart diseases is unknown. We tested the effects of a resveratrol-enriched diet on cardiovascular remodeling of chronic heart failure (CHF) in rats resulting from permanent ligation of left coronary artery. Two weeks after surgery, rats were started on either a resveratrol-enriched (R; 5 mg/kg per day; n = 23) or normal (Control; n = 23) diet for next 10 months. Serial echocardiography in Control showed a significant decline in LV ejection fraction, increases in LV end-systolic and end-diastolic volumes, and expansion in myocardial infarct from pre-treatment values. In R, compared with Control, there were substantial improvements in those parameters. End-point LV pressure-volume loop analysis showed a significantly improved LV systolic function and AV-coupling, an index of energy transfer efficacy between the heart and aortic tree, in R compared with Control (p < 0.05). Aortic pulse wave velocity, a measure of arterial stiffness, was significantly lower in R (389 ± 15 cm/s; p < 0.05) compared with Control (489 ± 38 cm/s). These results demonstrated that long-term dietary resveratrol supplement reduces cardiovascular structural and functional deterioration in CHF.

Linkage of Cardiac Gene Expression Profiles and ETS2 with Lifespan Variability in Rats

Longevity variability is a common feature of aging in mammals, but the mechanisms responsible for this remain largely unknown. Using microarray datasets coupled with prediction analysis of microarrays (PAM), we identified a set of 252 cardiac transcripts predictive of relative lifespan in Wistar and Fisher 344 rats. Prediction analysis of microarrays ‘tests’ of rat heart transcriptomes from a third longer lived Fisher × Norway Brown rat strain validated the predictive value of this gene subset. The expression patterns of these genes were highly conserved, and corresponding promoter regions were employed to identify common cis–elements and trans‐activating factors implicated in their control. Specifically, four transcription factors (Max, Ets2, Erg, and Msx2) present in heart displayed longevity‐dependent, strain‐independent changes in abundance, but only ETS2 had an expression profile that directly correlated with the relative lifespan gene set. In heart, ETS2 was prevalent in cardiomyocytes (CMs) and showed a high degree of myocyte‐to‐myocyte variability predominantly in adult rat hearts prior to the exponential increase in the rate of mortality. Exclusively in this group, elevated ETS2 significantly overlapped with TUNEL staining in heart myocytes. In response to sympathetic stimuli, ETS2 is also up‐regulated, and functionally, adenovirus‐mediated over‐expression of ETS2 promotes apoptosis‐inducing factor‐mediated, caspase‐independent programmed necrosis exclusively in CMs that can be fully inhibited by the PARP‐1 inhibitor DPQ. We conclude that variations in ETS2 abundance in hearts of adult rodents and the associated loss of CMs contribute at least partially, to the longevity variability observed during normal aging of rats through activation of programmed necrosis.

Vessel Ultrasound Sonographic Assessment of Soluble Receptor for Advanced Glycation End Products Efficacy in a Rat Balloon Injury Model

Objective We aimed to assess the therapeutic efficacy of differentially modified soluble receptor for advanced glycation end products (sRAGE) in vivo using vessel ultrasound sonography and to compare the sonography data with those from postmortem histomorphologic analyses to have a practical reference for future clinical applications. Methods Vessel ultrasound sonography was performed in a sRAGE-treated rat carotid artery balloon injury model at different time points after the surgery, and therapeutic efficacy of different doses of sRAGE produced in Chinese hamster ovary cells and with different N-glycoform modifications were assessed. Results Vessel ultrasound sonography found that sRAGE produced in Chinese hamster ovary cells with complex N-glycoform modifications is highly effective, and is consistent with our recent findings in the same model assessed with histology. We also found that sonography is less sensitive than histology when a higher dose of sRAGE is administered. Conclusions Sonograph results are consistent with those obtained from histology; that is, sRAGE produced in Chinese hamster ovary cells has significantly higher efficacy than insect cell-originated sRAGE cells.