Human cardiac tissues produce lower contractile stress and exhibit slower cross-bridge cycling in type 2 diabetes

Background: Diabetes mellitus elevates the risk of developing heart failure and increases associated mortality rates. While the clinical features of diabetic cardiomyopathy have been extensively studied, the effects of diabetes and associated changes in metabolic state on contractile cross-bridge function are less well-understood. Using our suite of experimental methods designed to measure cross-bridge kinetics and metabolite sensitivity, we aim to elucidate the mechanistic pathways by which cross-bridge alterations contribute to the organ-level dysfunction observed in diabetic cardiomyopathy. Methods: Atrial trabeculae from non-diabetic and type 2 diabetic patients without heart failure were perme- abilised and subjected to a series of experiments to measure their cross-bridge function and sensitivity to metabo- lites. Muscle active stress production and muscle active complex modulus measurements were gathered across different concentrations of ATP and inorganic phosphate (Pi) for the two groups of muscles. To link these func- tional data to tissue structural alterations, confocal imaging was performed to quantify the trabecula myofilament content and SWATH-MS was performed to measure the composition of myosin isoforms. Results: Diabetic trabeculae generated 20 % lower active stress and had 16 % lower cross-bridge stiffness on 15 average. The reduction in active stress production can be attributed to a lower density of myocytes in the diabetic muscles. The diabetic trabeculae also had a 24 % reduction in characteristic frequencies, reflecting slower cross- bridge cycling kinetics. This result was consistent with the measurement of a reduced fraction of the alpha myosin isoform in this group of patients. The interaction between diabetic status and metabolites was more complex. Although we found that diabetes did not affect the force response to changes in ATP or Pi concentrations, we found 20 that the stiffness of cross-bridges had a lower sensitivity to ATP in diabetic tissues. Conclusions: Our key results point to potential mechanisms of clinical dysfunction in diabetic heart tissue. Lower active force production in diabetic trabeculae suggests that these patients are developing systolic dysfunc- tion. Furthermore, slower cross-bridges can contribute to diastolic dysfunction, especially at higher heart rates, by prolonging cardiac relaxation.