Plasticity of Surface Structures and β 2 -Adrenergic Receptor Localization in Failing Ventricular Cardiomyocytes During Recovery From Heart Failure

Abstract

Background— Cardiomyocyte surface morphology and T-tubular structure are significantly disrupted in chronic heart failure, with important functional sequelae, including redistribution of sarcolemmal β 2 -adrenergic receptors (β 2 AR) and localized secondary messenger signaling. Plasticity of these changes in the reverse remodeled failing ventricle is unknown. We used AAV9.SERCA2a gene therapy to rescue failing rat hearts and measured z-groove index, T-tubule density, and compartmentalized β 2 AR-mediated cAMP signals, using a combined nanoscale scanning ion conductance microscopy-Förster resonance energy transfer technique. Methods and Results— Cardiomyocyte surface morphology, quantified by z-groove index and T-tubule density, was normalized in reverse-remodeled hearts after SERCA2a gene therapy. Recovery of sarcolemmal microstructure correlated with functional β 2 AR redistribution back into the z-groove and T-tubular network, whereas minimal cAMP responses were initiated after local β 2 AR stimulation of crest membrane, as observed in failing cardiomyocytes. Improvement of β 2 AR localization was associated with recovery of βAR-stimulated contractile responses in rescued cardiomyocytes. Retubulation was associated with reduced spatial heterogeneity of electrically stimulated calcium transients and recovery of myocardial BIN-1 and TCAP protein expression but not junctophilin-2. Conclusions— In summary, abnormalities of sarcolemmal structure in heart failure show plasticity with reappearance of z-grooves and T-tubules in reverse-remodeled hearts. Recovery of surface topology is necessary for normalization of β 2 AR location and signaling responses.