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

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 (Lys(6), Lys(39)), thirteen troponin-I residues (Lys(36), Lys(50), Lys(58), Arg(79), Lys(117), Lys(120), Lys(131), Arg(148), Arg(162), Lys(164), Lys(183), Lys(193), Arg(204)), and three troponin-T residues (Lys(107), Lys(125), Lys(227)). AGE modifications of three corresponding troponin-I residues (Lys(58), Lys(120), Lys(194)) and two corresponding troponin-T residues (Lys(107), Lys(227)) were confirmed in cardiac tissue extracts from an experimental rodent diabetic model. Additionally, novel human troponin-I phosphorylation sites were detected (Thr(119), Thr(123)). 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.