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      Effects of Advanced Glycation End Products on Calcium Handling in Cardiomyocytes

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          Background and Aims: Advanced glycation end products (AGEs) accumulate in diabetes and the engagement of receptor for AGE (RAGE) by AGEs contributes to the pathogenesis of diabetic cardiomyopathy. This study aims to investigate the effects of AGE/RAGE on ryanodine receptor (RyR) activity and Ca<sup>2+</sup> handling in cardiomyocytes to elucidate the possible mechanism underlying cardiac dysfunction in diabetic cardiomypathy. Methods and Results: Confocal imaging Ca<sup>2+</sup> spark, the elementary Ca<sup>2+</sup> release event reflecting RyR activity in intact cell, as well as SR Ca<sup>2+</sup> content and systolic Ca<sup>2+</sup> transient were performed in cultured neonatal rat ventricular myocytes. The results show that 50 mg/ml AGE increased the frequency of Ca<sup>2+</sup> sparks by 160%, while 150 mg/ml AGE increased it by 53%. AGE decreased the amplitude, width and duration of Ca<sup>2+</sup> sparks. Blocking RAGE with anti-RAGE IgG completely abolished the alteration of Ca<sup>2+</sup> sparks. The SR Ca<sup>2+</sup> content indicated by the amplitude (ΔF/F0) of 20 m<smlcap>M</smlcap> caffeine-elicited Ca<sup>2+</sup> transient was significantly decreased by 150 mg/ml AGE. In parallel, the amplitude of systolic Ca<sup>2+</sup> transient evoked by 1 Hz-field stimulation was remarkably decreased by 150 mg/ml AGE. The anti-RAGE antibody completely restored the impaired SR load and systolic Ca<sup>2+</sup> transient. Conclusion: AGE/RAGE signal enhanced Ca<sup>2+</sup> spark-mediated SR Ca<sup>2+</sup> leak, causing partial depletion of SR Ca<sup>2+</sup> content and consequently decreasing systolic Ca<sup>2+</sup> transient, which may contribute to contractile dysfunction in diabetic cardiomyopathy.

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          Most cited references 19

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          Advanced glycation end products and RAGE: a common thread in aging, diabetes, neurodegeneration, and inflammation.

          The products of nonenzymatic glycation and oxidation of proteins and lipids, the advanced glycation end products (AGEs), accumulate in a wide variety of environments. AGEs may be generated rapidly or over long times stimulated by a range of distinct triggering mechanisms, thereby accounting for their roles in multiple settings and disease states. A critical property of AGEs is their ability to activate receptor for advanced glycation end products (RAGE), a signal transduction receptor of the immunoglobulin superfamily. It is our hypothesis that due to such interaction, AGEs impart a potent impact in tissues, stimulating processes linked to inflammation and its consequences. We hypothesize that AGEs cause perturbation in a diverse group of diseases, such as diabetes, inflammation, neurodegeneration, and aging. Thus, we propose that targeting this pathway may represent a logical step in the prevention/treatment of the sequelae of these disorders.
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            Redox modification of ryanodine receptors contributes to sarcoplasmic reticulum Ca2+ leak in chronic heart failure.

            Abnormal cardiac ryanodine receptor (RyR2) function is recognized as an important factor in the pathogenesis of heart failure (HF). However, the specific molecular causes underlying RyR2 defects in HF remain poorly understood. In the present study, we used a canine model of chronic HF to test the hypothesis that the HF-related alterations in RyR2 function are caused by posttranslational modification by reactive oxygen species generated in the failing heart. Experimental approaches included imaging of cytosolic ([Ca(2+)](c)) and sarcoplasmic reticulum (SR) luminal Ca(2+) ([Ca(2+)]SR) in isolated intact and permeabilized ventricular myocytes and single RyR2 channel recording using the planar lipid bilayer technique. The ratio of reduced to oxidized glutathione, as well as the level of free thiols on RyR2 decreased markedly in failing versus control hearts consistent with increased oxidative stress in HF. RyR2-mediated SR Ca(2+) leak was significantly enhanced in permeabilized myocytes, resulting in reduced [Ca(2+)](SR) in HF compared to control cells. Both SR Ca(2+) leak and [Ca(2+)](SR) were partially normalized by treating HF myocytes with reducing agents. Conversely, oxidizing agents accelerated SR Ca(2+) leak and decreased [Ca(2+)](SR) in cells from normal hearts. Moreover, exposure to antioxidants significantly improved intracellular Ca(2+)-handling parameters in intact HF myocytes. Single RyR2 channel activity was significantly higher in HF versus control because of increased sensitivity to activation by luminal Ca(2+) and was partially normalized by reducing agents through restoring luminal Ca(2+) sensitivity oxidation of control RyR2s enhanced their luminal Ca(2+) sensitivity, thus reproducing the HF phenotype. These findings suggest that redox modification contributes to abnormal function of RyR2s in HF, presenting a potential therapeutic target for treating HF.
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              Decreased sarcoplasmic reticulum activity and contractility in diabetic db/db mouse heart.

              Although it is known that insulin-dependent (type 1) diabetes results in depressed contractile performance associated with diminished sarcoendoplasmic reticular Ca2+-ATPase (SERCA2a) activity, findings in insulin-resistant (type 2) diabetes suggest a less clear association. The db/db insulin-resistant mouse model exhibits decreased cardiac performance both in situ and in isolated ex vivo working hearts. In this study, contractile performance and calcium transients were measured in Langendorff-perfused hearts and isolated cardiac myocytes. Diabetic (db/db) mouse hearts demonstrated decreased rates of contraction, relaxation, and pressure development. Calcium transients from isolated myocytes revealed significantly lower diastolic and systolic levels of calcium in diabetic hearts. Furthermore, the decay rate of the calcium transient was significantly reduced in diabetic myocytes, suggesting a diminished capacity for cytosolic calcium removal not associated with a change in sodium-calcium exchanger activity. Calcium leakage from the sarcoplasmic reticulum (SR) measured using tetracaine was significantly increased in diabetic myocytes. Western blot analysis indicated only a small decrease in SERCA2a expression in diabetic mice, but a large increase in phospholamban expression. Expression of the ryanodine receptor did not differ between groups. In conclusion, the decreased contractile function observed in the db/db diabetic mouse model appears to be related to decreased calcium handling by the SR.

                Author and article information

                S. Karger AG
                September 2014
                19 August 2014
                : 129
                : 2
                : 75-83
                aDepartment of Endocrinology, The First Affiliated Hospital of Shenzhen University, Shenzhen, bDepartment of Pathophysiology, School of Medicine, Shenzhen University, Shenzhen, cDepartment of Anesthesiology, Shenzhen People's Hospital, 2nd Clinical Medical College of Jinan University, Shenzhen, and dDepartment of Pathophysiology, Southern Medical School, Guangzhou, China
                Author notes
                *Jie Liu, MD, PhD, School of Medicine, Shenzhen University, Shenzhen, Guangdong 518060 (China), E-Mail
                364779 Cardiology 2014;129:75-83
                © 2014 S. Karger AG, Basel

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                Page count
                Figures: 7, Pages: 9
                Original Research


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