Cardiac troponins may be irreversibly modified by glycation: novel potential mechanisms of cardiac performance modulation

Abstract

Dynamic movements of the cardiac troponin complex are an important component of the cardiac cycle. Whether cardiac troponins are subjected to irreversible advanced glycation end-product (AGE) modification is unknown. This study interrogated human and rat cardiac troponin-C, troponin-I and troponin-T to identify endogenous AGE modifications using mass spectrometry (LC-MS/MS). AGE modifications were detected on two amino acid residues of human troponin-C (Lys6, Lys39), thirteen troponin-I residues (Lys36, Lys50, Lys58, Arg79, Lys117, Lys120, Lys131, Arg148, Arg162, Lys164, Lys183, Lys193, Arg204), and three troponin-T residues (Lys107, Lys125, Lys227). AGE modifications of three corresponding troponin-I residues (Lys58, Lys120, Lys194) and two corresponding troponin-T residues (Lys107, Lys227) were confirmed in cardiac tissue extracts from an experimental rodent diabetic model. Additionally, novel human troponin-I phosphorylation sites were detected (Thr119, Thr123). Accelerated AGE modification of troponin-C was evident in vitro with hexose sugar exposure. This study provides the first demonstration of the occurrence of cardiac troponin complex AGE-modifications. These irreversible AGE modifications are situated in regions of the troponin complex known to be important in myofilament relaxation, and may be of particular pathological importance in the pro-glycation environment of diabetic cardiomyopathy.

Acute total body ionizing gamma radiation induces long-term adverse effects and immediate changes in cardiac protein oxidative carbonylation in the rat

“…While this is the first report of cTnT carbonylation, other post translational modifications, such as phosphorylation, methionine oxidation, and glycosylation have been previously reported for cardiac troponin T, I, and C subunits present in myocardial contractile machinery [49][50][51]. The irreversible oxidative carbonylation can act as an alternative mechanism by which the protein may be dissociated from its complex in the myocardium and subsequently released into the blood.…”

Site-specific acetyl-mimetic modification of cardiac troponin I modulates myofilament relaxation and calcium sensitivity

“…The detailed fragmentation spectrum showing b and y ion identification confirms the site-specific acetylation of K132 on TnI. B. Schematic illustrating troponin I binding regions demonstrating the location of the common lysines (4: K107, K132, K178, K194) found to be acetylated in cTnI by proteomic screens in rat and guinea pig [10,12]. K132 is within a region that binds cTnC and in the actin binding region.…”

“…These changes influence both the calcium sensitivity of myofilament steadystate isometric force production as well relaxation kinetics [1,7]. While phosphorylation has been the most studied PTM of sarcomeric proteins, it has become evident that many different modifications occur normally and in disease, including acetylation, glycation, oxidation, citrullination, and succinylation [8][9][10][11][12]. These PTMs have the potential to impact sarcomeric protein interactions and thereby alter the properties of contraction and relaxation.…”

Elevated myocardial fructose and sorbitol levels are associated with diastolic dysfunction in diabetic patients, and cardiomyocyte lipid inclusions in vitro

“…We have previously shown that the fructose-specific transporter GLUT5 is expressed in cardiomyocytes and provided evidence that fructose availability can modulate cardiomyocyte excitation-contraction coupling in vitro 12 . Additionally, fructose can directly impact structure and function of proteins via post-translational modifications which are both irreversible (advanced glycation end-products) and reversible (O-GlcNAcylation) 4 , 13 . The detrimental actions of fructose have been most well described in the liver, where increased fructose has been linked to lipid accumulation, ATP depletion, and insulin resistance 14 .…”