Effects Of Advanced Glycation End Products On Calcium Handling In Cardiomyocytes

Advanced glycation end products (AGE), the products of nonenzymatiac glyca-tion and oxidation of proteins and lipids, accumulate in diverse biological settings,su-ch as diabetes, inflammation, renal failure and aging. The receptor for AGE (RAGE) is the best characterized cell surface molecule that recognizes AGE and has been sho-wn to be expressed in various organs including the heart The engagement of RAGE by AGE in a variety of settings triggers rapid generation of reactive oxygen species (ROS) and the upregulation of inflammatory pathways Recent studies indicate that accumulation of AGE in heart tissue and AGE/RAGE interaction contr-ibutes to the pathogenesis of diabetic cardiomyopathy A prominent manifestation of diabetic cardiomyopathy is cardiac contractile dysfunction. However, the mechanisms underlying the development of contractile dysfunction of the heart are largely unknown.Ca2+ plays an essential role in cardiac excitation contraction coupling. In mammalian heart, the major source of Ca2+ or contractile activation is sarcoplasmic reticulum (SR). In systole, large amounts of Ca2+ are released from SR upon depolarization induced Ca2+ influx, giving rise to an intracellular Ca2+ transient that triggers myofilament contraction The ryanodine receptor (RyR) in SR gates Ca 2+release from SR via the Ca2+ induced Ca2+ release mechanism. Meanwhile, the activity of RyR in diastole determines the occurrence of sporadic Ca2+ sparks, the elementary intracellular Ca2+release from 4-6 neighboring RyRs, controlling SR Ca 2+ content. Abnormal RyR function has been demonstrated to induce cardiac dysfunction of various causes, such as ischemia-reperfusion, hypertrophy and heart failure. In myocardial ischemia-reperfusion, a hyperactive RyR-mediated SR Ca 2+leak has been suggested to contribute to ventricular arrhythmia, myocardial infarction and left ventricular re-modeling In failing heart, SR Ca2+ leak impairs cardiac contractile function and induces ventricular arrhythmia Abnormal RyR function has also been demonstrated in streptozotocin-induced typeldiabetes,although the pathological significance is not well characterized.The interaction of AGE/RAGE has been suggested to impair cardiac Ca2+ handling by reducing the systolic and diastolic intracellular Ca2+ concentration and prolonging the decay time of the Ca2+ transient Whether AGE/RAGE modulates RyR function and impairs Ca2+ handling remains unknown. It is well documented that RyR is sensitive to the intracellular redox status due to rich free thiol groups in its structure. An increase in intracellular oxidative stress upregulates RyR activity, re-sulting in an SR leak Given that the AGE/RAGE signal induces ROS overproduction, we hypothesized that the AGE/RAGE signal increased SR Ca2+ leak by increasing RyR activity and consequently impairing cardiac Ca2+ homeostasis. In this study, we tested this hypothesis and confirmed that AGE/RAGE induced hyperactive RyRs in cardiomyocytes by enhancing oxidative stress in RyRs. Furthermore, we demonstrated that the hyperactive RyR mediated SR leak reduced SR Ca2+ content, resulting in a decrease in the systolic Ca2+ transient.Object:Advanced glycation end products (AGEs) accumulate in diabetes and the engagbement of receptor for AGE (RAGE) by AGEs contributes to the pathogensis of diabetic cardiomyopathy. This study aims to investigate the effects of AGE/RAGE on ryanodine receptor (RyR) activity and Ca2+ handling in cardiomyocytes to elucidate the possible mechanism underlying cardiac dysfunction in diabetic cardiomypathy.Methods:Confocal imaging Ca2+ spark, the elementary Ca2+ release event reflecting RyR activity in intact cell, as well as SR Ca2+ content and systolic Ca2+ transient were performed in cultured neonatal rat ventricular myocytes.Results:The results show that 50 mg/ml AGE increased the frequency of Ca2+ sparks by 160%, while 150 mg/ml AGE increased it by 53%. AGE decreased the amplitude, width and duration of Ca2+ sparks. Blocking RAGE with anti-RAGE IgG completely abolished the alteration of Ca2+ sparks. The SR Ca2+ content indicated by the amplitude caffeine-elicited Ca2+ transient was significantly decreased by 150 mg/ml AGE. In parallel, the amplitude of systolic Ca2+ 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 Ca2+ transient. Conclusion: AGE/RAGE signal enhanced Ca2+ spark-mediated SR Ca2+ leak, causing partial depletion of SR Ca2+ content and consequently decreasing systolic Ca2+ transient, which may contribute to contractile dysfunction in diabetic cardiomyopathy.