Super-Resolution 3D Imaging Reveals Disarray of Dyadic Calcium Ion Channels in Failing Hearts Expressing Low Thyroid Hormone Function

Ventricular remodeling occurring in heart failure (HF) involves structural disarray of the sarcolemma T-tubule (TT)–sarcoplasmic reticulum (SR) dyad junctions, thereby disrupting the close apposition of L-type Ca2+ channels (CaV1.2) with ryanodine receptors (RyR2) that trigger SR Ca2+ release and myofilament contraction. In a rat ischemic heart failure model expressing low thyroid hormone (TH) function, we used 3D stochastic optical reconstruction microscopy (STORM) to image RyR2 clusters with CaV1.2 channels, and the associated protein junctophilin-2 (Jph2). We tested whether treatment with T3, the biologically active form of TH, throughout progression of the disease would preserve T-tubule structure and dyadic ion channel organization. Confocal microscopy of isolated cardiomyocytes (CMs) stained with ANEPPS membrane dye showed significantly decreased TT density in diseased CMs while T3 treatment attenuated TT disorganization. 3D STORM images of dyadic ion channels labeled with fluorescent-tagged antibodies to RyR-Dylight550, Jph-CF647 and CaV1.2/IgG-Dylight488 were captured. A density-based algorithm defined RyR2 clusters, and a 400 nm spherical 3D volume of interest around each RyR2 cluster’s centroid determined the number of CaV1.2 and Jph2 localizations associated with each RyR2 cluster. Analysis revealed significant reduction in RyR2 cluster size and number with reduced co-localized Jph2 in failing CMs. T3 treatment increased RyR2 cluster numbers and cluster volumes albeit non-significantly, with increased co-clustering of Jph2. The number of CaV1.2 co-localized with RyR2 clusters trended lower in the failing CMs. These results support maintaining TH homeostasis in optimizing the nanoscale organization of Ca2+ ion channels in triggering Ca2+ release and myofibrillar contraction in patients with heart disease.