Diabetes and the Female Heart

Abstract

Type 2 diabetes is a major risk factor for heart failure, with diabetic women experiencing disproportionately severe outcomes compared to diabetic men. The mechanisms underlying these sex specific outcomes remain unclear. This thesis investigated how sex and type 2 diabetes interact to influence cardiac mechanics, energetics, and structure, focusing on cardiac excitation contraction coupling (ECC) - a critical cellular event that leads to heart muscle contraction. To achieve the project aim, I developed and applied an integrated experimental pipeline combining diabetic rat preparation, work loop calorimetry and immunofluorescence structural imaging. Four key objectives guided this work. First, I characterised, using a work-loop calorimeter, baseline sex‑differences in mechanoenergetics of isolated healthy trabeculae, to understand differences in indices of functional performance including activation heat, cross-bridge heat, force length work output, and mechanical efficiency between males and females. Second, I investigated to establish a type 2 diabetes model in both sexes using a high-fat diet and low-dose streptozotocin injections. Third, using the work-loop calorimeter, I studied isolated diabetic left ventricular trabeculae to assess whether cardiac mechanoenergetics were sex- and diabetes-dependent. Finally, I employed super-resolution Stimulated Emission Depletion (STED) microscopy and automated image analysis pipelines to quantify key ECC proteins organisation: transverse tubules (T tubule), ryanodine receptor type 2 (RyR2) clusters, and filamentous actin (F-actin). Results showed that while diabetic rats developed systemic dysfunction including glucose intolerance and alterations in plasma biomarkers, myocardial energetics were preserved at the trabecula level. Baseline comparisons revealed no sex differences in mechanoenergetic indices in healthy muscle. In the diabetic model, neither sex nor diabetes altered twitch kinetics, energetic cost, and mechanical efficiency over a wide range of workloads, indicating preserved mechanoenergetic performance despite systemic disease. Structural analyses revealed clear spatial disorganisation only in diabetic males, with reduced T-tubule area alongside enlarged RyR2 clusters. F-actin organisation remained unchanged in all groups. Collectively, this work provides the first direct quantification of sex-specific cardiac mechanoenergetic performance in type 2 diabetes and links structural to function. By integrating functional and structural investigation, this thesis establishes a framework for future research into diabetic cardiomyopathy and highlights the importance of incorporating sex as a biological variable in cardiovascular research