Background: In cardiomyocytes from patients with hypertrophic cardiomyopathy, mechanical dysfunction and arrhythmogenicity are caused by mutation‐driven changes in myofilament function combined with excitation‐contraction (E‐C) coupling abnormalities related to adverse remodeling. Whether myofilament or E‐C coupling alterations are more relevant in disease development is unknown. Here, we aim to investigate whether the relative roles of myofilament dysfunction and E‐C coupling remodeling in determining the hypertrophic cardiomyopathy phenotype are mutation specific. Methods and Results: Two hypertrophic cardiomyopathy mouse models carrying the R92Q and the E163R TNNT2 mutations were investigated. Echocardiography showed left ventricular hypertrophy, enhanced contractility, and diastolic dysfunction in both models; however, these phenotypes were more pronounced in the R92Q mice. Both E163R and R92Q trabeculae showed prolonged twitch relaxation and increased occurrence of premature beats. In E163R ventricular myofibrils or skinned trabeculae, relaxation following Ca ²⁺ removal was prolonged; resting tension and resting ATPase were higher; and isometric ATPase at maximal Ca ²⁺ activation, the energy cost of tension generation, and myofilament Ca ²⁺ sensitivity were increased compared with that in wild‐type mice. No sarcomeric changes were observed in R92Q versus wild‐type mice, except for a large increase in myofilament Ca ²⁺ sensitivity. In R92Q myocardium, we found a blunted response to inotropic interventions, slower decay of Ca ²⁺ transients, reduced SERCA function, and increased Ca ²⁺ /calmodulin kinase II activity. Contrarily, secondary alterations of E‐C coupling and signaling were minimal in E163R myocardium. Conclusions: In E163R models, mutation‐driven myofilament abnormalities directly cause myocardial dysfunction. In R92Q, diastolic dysfunction and arrhythmogenicity are mediated by profound cardiomyocyte signaling and E‐C coupling changes. Similar hypertrophic cardiomyopathy phenotypes can be generated through different pathways, implying different strategies for a precision medicine approach to treatment.

The early phases of embryonic development and cancer share similar strategies to improve their survival in an inhospitable environment: both proliferate in a hypoxic and catecholamine‐rich context, increasing aerobic glycolysis. Recent studies show that β3‐adrenergic receptor (β3‐AR) is involved in tumor progression, playing an important role in metastasis. Among β‐adrenergic receptors, β3‐AR is the last identified member of this family, and it is involved in cancer cell survival and induction of stromal reactivity in the tumor microenvironment. β3‐AR is well known as a strong activator of uncoupling protein 1 (UCP1) in brown fat tissue. Interestingly, β3‐AR is strongly expressed in early embryo development and in many cancer tissues. Induction of uncoupling protein 2 (UCP2) has been related to cancer metabolic switch, leading to accelerated glycolysis and reduced mitochondrial activity. In this study, for the first time, we demonstrate that β3‐AR is able to promote this metabolic shift in both cancer and embryonic stem cells, inducing specific glycolytic cytoplasmic enzymes and a sort of mitochondrial dormancy through the induction of UCP2. The β3‐AR/UCP2 axis induces a strong reduction of mitochondrial activity by reducing ATP synthesis and mitochondrial reactive oxygen species (mtROS) content. These effects are reverted by SR59230A, the specific β3‐AR antagonist, causing an increase in mtROS. The increased level of mtROS is neutralized by a strong antioxidant activity in embryonic stem cells, but not in cancer stem cells, where it causes a dramatic reduction in tumor cell viability. These results lead to the possibility of a selective antitumor therapeutic use of SR59230A. Notably, we demonstrate the presence of β3‐AR within the mitochondrial membrane in both cell lines, leading to the control of mitochondrial dormancy.

Maturation of human embryonic stem cell-derived cardiomyocytes (hESC-CM) is accompanied by changes in ion channel expression, with relevant electrophysiological consequences. In rodent CM, the properties of hyperpolarization-activated cyclic nucleotide-gated channel (HCN)4, a major f-channel isoform, depends on the association with caveolin-3 (Cav3). To date, no information exists on changes in Cav3 expression and its associative relationship with HCN4 upon hESC-CM maturation. We hypothesize that Cav3 expression and its compartmentalization with HCN4 channels during hESC-CM maturation accounts for the progression of f-current properties toward adult phenotypes. To address this, hESC were differentiated into spontaneously beating CM and examined at ∼30, ∼60, and ∼110 days of differentiation. Human adult and fetal CM served as references. HCN4 and Cav3 expression and localization were analyzed by real time PCR and immunocyto/histochemistry. F-current was measured in patch-clamped single cells. HCN4 and Cav3 colocalize in adult human atrial and ventricular CM, but not in fetal CM. Proteins and mRNA for Cav3 were not detected in undifferentiated hESC, but expression increased during hESC-CM maturation. At 110 days, HCN4 appeared to be colocalized with Cav3. Voltage-dependent activation of the f-current was significantly more positive in fetal CM and 60-day hESC-CM (midpoint activation, V_1/2, ∼ −82 mV) than in 110-day hESC-CM or adult CM (V_1/2∼−100 mV). In the latter cells, caveolae disruption reversed voltage dependence toward a more positive or an immature phenotype, with V_1/2 at −75 mV, while in fetal CM voltage dependence was not affected. Our data show, for the first time, a developmental change in HCN4-Cav3 association in hESC-CM. Cav3 expression and its association with ionic channels likely represent a crucial step of cardiac maturation.