Chronic Diabetes Increases Advanced Glycation End Products on Cardiac Ryanodine Receptors/Calcium-Release Channels

Abstract

Decrease in cardiac contractility is a hallmark of chronic diabetes. Previously we showed that this defect results, at least in part, from a dysfunction of the type 2 ryanodine receptor calcium-release channel (RyR2). The mechanism(s) underlying RyR2 dysfunction is not fully understood. The present study was designed to determine whether non-cross-linking advanced glycation end products (AGEs) on RyR2 increase with chronic diabetes and if formation of these post-translational complexes could be attenuated with insulin treatment. Overnight digestion of RyR2 from 8-week control animals (8C) with trypsin afforded 298 peptides with monoisotopic mass (M؉H ؉ ) >500. Digestion of RyR2 from 8-week streptozotocin-induced diabetic animals (8D) afforded 21% fewer peptides, whereas RyR2 from 6-week diabetic/2-week insulin-treated animals generated 304 peptides. Using an in-house PERLscript algorithm, search of matrix-assisted laser desorption ionization-time of flight mass data files identified several M؉H ؉ peaks corresponding to theoretical RyR2 peptides with single N ⑀ -(carboxymethyl)-lysine, imidazolone A, imidazone B, pyrraline, or 1-alkyl-2-formyl-3,4-glycosyl pyrrole modification that were present in 8D but not 8C. Insulin treatment minimized production of some of these nonenzymatic glycation products. These data show for the first time that AGEs are formed on intracellular RyR2 during diabetes. Because AGE complexes are known to compromise protein activity, these data suggest a potential mechanism for diabetesinduced RyR2 dysfunction. Diabetes 52:1825-1836, 2003 A significant percentage of patients with diabetes (both type 1 and type 2) develop a unique cardiomyopathy that is independent of coronary atherosclerosis (1-3). This "diabetic cardiomyopathy" as it is termed starts off with asymptomatic left ventricular diastolic dysfunction (slowing of relaxation kinetics). As the disease progresses, systolic function becomes compromised, leading to an increase in incidence of morbidity and mortality (4 -6).The release of calcium ions from internal sarcoplasmic reticulum via the type 2 ryanodine receptor calciumrelease channel (RyR2) is an integral step in the cascade of events leading to cardiac muscle contraction (7). We and others have shown that expression of this protein decreases in hearts of chronic diabetic patients (8,9) as well as in the streptozotocin (STZ)-induced diabetic rats (10 -13). Using the latter model, we found that in addition to a decrease in expression of RyR2, its functional integrity is also compromised in diabetes (14,15). This dysfunction is manifested as a decrease in RyR2 ability to bind the specific ligand [ 3 H]ryanodine and a slowing in its electrophoretic mobility using denaturing SDS-PAGE.Two distinct and separate types of post-translational modifications are likely to be induced by diabetes. First, it is well known that metabolic changes brought about by diabetes increase production of reactive oxygen species (e.g., -18]). These free radical and nonradical species react with several a...

Treinamento em natação atenua a disfução contrátil de cardiomiócitos de ratos diabéticos

“…There is evidence that the intracellular concentration of Ca 2+ is reduced in cardiomyocytes of animals with experimental diabetes 23 . This occurs due to the increased activity of sodium and calcium exchanger (NCX) and decreased uptake of Ca 2+ by the sarcoplasmic reticulum (SR) via calcium ATPase of the SR (SERCA2) 15 and reduced release of Ca 2+ of SR, via ryanodine receptors (RyR2) 24 . Moreover, it is possible that the reduced density of transverse tubules in cardiomyocytes of diabetic animals can change the space between the L-type calcium channels and RyR2, which reduces the efficiency of excitation-contraction coupling 15 .…”

“…The speed of contraction of cardiomyocytes is controlled by proteins that regulate intracellular Ca 2+ movement and the rate of ATP hydrolysis which, in turn, regulates the rate of formation of crossed bridges 21 . Cardiomyocytes of diabetic animals reduce the expression of regulatory proteins such as CaMKII, NCX, RyR2, SERCA2 and phospholamban (PLB) 5,7,15,[24][25][26] , which may delay the availability of Ca 2+ for cell contraction.…”

“…Another program of continuous running with high intensity (18 m/ min, 5.0% inclination, 60 min/day) led to negative changes, as it prolonged cell contraction time and did not alter the amplitude of contraction of rat cardiomyocytes 14 . However, running programs on a treadmill with higher intensity (20)(21)(22)(23)(24)(25)Introduction Diabetes mellitus type 1 is a risk factor for cardiovascular events, including the development of diabetic cardiomyopathy. The inability to maintain glucose homeostasis in the myocardium compromises cardiac structure and function in humans and animals with experimental diabetes [1][2][3][4] .…”

Insulin Resistance and Cardiomyopathy

“…On the other hand, hyperglycemia also shifts the glucose glycolytic pathway into alternative pathways that are considered mediators of hyperglycemia induced cellular injury (26). The damage resulting from hyperglycemia includes elevation of advanced glycation end products (AGEs), hexosamine and polyol pathway, activation of beta 2 isoform PKC and alteration of myocardial structure and function (41)(42)(43)(44)(45)(46)(47). In addition, it has been suggested that hyperglycemia is linked to altering the expression and function of both the ryanodine receptor (RyR) and sarco/endoplasmic reticulum Ca 2+ -ATPase (SERCA), and this alteration may contribute to impair myocardial systolic and diastolic function (26).…”

Upregulation of Ryanodine Receptor Calcium Channels (RyR2) in Rats with Induced Diabetes after 4 Weeks of High Intensity Interval Training

“…Diabetic cardiomyopathy has been diagnosed in clinical and animal diabetic models without any symptom of vascular damage (2). At molecular level, these changes are probably derived from changes in expression and/or activity of various proteins involved in maintaining or regulating intracellular calcium homeostasis (3,4). Ryanodine receptors (RyR2) are among these groups of proteins.…”