Compartment-specific cAMP dysfunction in diabetic cardiomyopathy in hiPSC-derived cardiomyocytes: therapeutic potential of fibroblast growth factor 1

Background Diabetic cardiomyopathy (DCM) represents a distinct form of heart failure occurring independently of coronary artery disease, yet effective treatments remain limited. While cAMP signaling alterations have been reported in diabetic hearts, the compartment-specific consequences across distinct subcellular pools remain poorly understood. We investigated cytosolic and mitochondrial cAMP microdomain dysfunction in DCM, focusing on ADCY2 and PDE4DIP as potential regulators, and evaluated fibroblast growth factor 1 (FGF1) as a therapeutic intervention using integrated two-dimensional (2D) and three-dimensional (3D) human induced pluripotent stem cell (hiPSC)-derived cardiac models. Methods Healthy hiPSC-derived cardiomyocytes were exposed to a diabetic-like environment (high glucose, endothelin-1 and cortisol) in 2D and 3D culture. Two-dimensional studies included bulk RNA sequencing, FRET-based cAMP measurements in cytosolic and mitochondrial outer membrane compartments, and microelectrode array electrophysiology. Three-dimensional cardiac microtissues were assessed by optical mapping to characterize spatial calcium dynamics and conduction properties. Results DCM exhibited compartment-specific cAMP dysregulation associated with ADCY2 downregulation and PDE4DIP upregulation. Cytosolic compartments showed preserved baseline cAMP but attenuated forskolin responsiveness, while the mitochondrial outer membrane displayed both reduced baseline cAMP and impaired stimulated responses. Transcriptomic analysis revealed transcriptional signatures consistent with metabolic remodeling, including upregulated fatty acid oxidation machinery, Complex I dysfunction, and elevated phospholamban and CASQ2 expression. 3D optical mapping demonstrated reduced calcium transient amplitude, prolonged transient duration, and severely impaired calcium propagation velocity. FGF1 treatment normalized PDE4DIP expression and restored cAMP dynamics in 2D cultures and partially improved calcium transient amplitude in 3D microtissues, though conduction defects persisted. Conclusions Compartment-specific impairment of cAMP microdomains is associated with DCM pathogenesis. Integrated 2D–3D assessment reveals that FGF1 improves cAMP signaling but does not fully reverse metabolic, electrophysiological, or structural abnormalities, highlighting the need for combination therapies targeting both cAMP pathway integrity and conduction restoration.