Cardiomyocyte Na+ and Ca2+ mishandling drives vicious cycle involving CaMKII, ROS, and ryanodine receptors.

Cardiomyocyte Na+ and Ca2+ mishandling, upregulated Ca2+/calmodulin-dependent kinase II (CaMKII), and increased reactive oxygen species (ROS) are characteristics of various heart diseases, including heart failure (HF), long QT (LQT) syndrome, and catecholaminergic polymorphic ventricular tachycardia (CPVT). These changes may form a vicious cycle of positive feedback to promote cardiac dysfunction and arrhythmias. In HF rabbit cardiomyocytes investigated in this study, the inhibition of CaMKII, late Na+ current (INaL), and leaky ryanodine receptors (RyRs) all attenuated the prolongation and increased short-term variability (STV) of action potential duration (APD), but in age-matched controls these inhibitors had no or minimal effects. In control cardiomyocytes, we enhanced RyR leak (by low [caffeine] plus isoproterenol mimicking CPVT) which markedly increased STV and delayed afterdepolarizations (DADs). These proarrhythmic changes were significantly attenuated by both CaMKII inhibition and mitochondrial ROS scavenging, with a slight synergy with INaL inhibition. Inducing LQT by elevating INaL (by Anemone toxin II, ATX-II) caused markedly prolonged APD, increased STV, and early afterdepolarizations (EADs). Those proarrhythmic ATX-II effects were largely attenuated by mitochondrial ROS scavenging, and partially reduced by inhibition of CaMKII and pathological leaky RyRs using dantrolene. In human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) bearing LQT3 mutation SCN5A N406K, dantrolene significantly attenuated cell arrhythmias and APD prolongation. Targeting critical components of the Na+-Ca2+-CaMKII-ROS-INaL arrhythmogenic vicious cycle may exhibit important on-target and also trans-target effects (e.g., INaL and RyR inhibition can alter INaL-mediated LQT3 effects). Incorporating this vicious cycle into therapeutic strategies provides novel integrated insight for treating cardiac arrhythmias and diseases.

Predictive Male-to-Female Translation of Cardiac Electrophysiological Response to Drugs.

Despite evidence that women are at higher risk of drug-induced torsade de pointes and sudden cardiac death, female sex is vastly underrepresented in cardiovascular research, thus limiting our fundamental understanding of sex-specific arrhythmia mechanisms and our ability to predict arrhythmia propensity. To address this urgent clinical and preclinical need, we developed a quantitative tool that predicts the electrophysiological response to drug administration in female cardiomyocytes starting from data collected in males. We demonstrate the suitability of our translator for sex-specific cardiac safety assessment and include proof-of-concept application of our translator to in vitro and in vivo data.

Sex-dependent effects of developmental hypoxia on cardiac mitochondria from adult murine offspring.

Insufficient oxygen supply (hypoxia) during fetal and embryonic development can lead to latent phenotypical changes in the adult cardiovascular system, including altered cardiac function and increased susceptibility to ischemia reperfusion injury. While the cellular mechanisms underlying this phenomenon are largely unknown, several studies have pointed towards metabolic disturbances in the heart of offspring from hypoxic pregnancies. To this end, we investigated mitochondrial function in the offspring of a mouse model of prenatal hypoxia. Pregnant C57 mice were subjected to either normoxia (21%) or hypoxia (14%) during gestational days 6-18. Offspring were reared in normoxia for up to 8 months and mitochondrial biology was assessed with electron microscopy (ultrastructure), spectrophotometry (enzymatic activity of electron transport chain complexes), microrespirometry (oxidative phosphorylation and H202 production) and Western Blot (protein expression). Our data showed that male adult offspring from hypoxic pregnancies possessed mitochondria with increased H202 production and lower respiratory capacity that was associated with reduced protein expression of complex I, II and IV. In contrast, females from hypoxic pregnancies had a higher respiratory capacity and lower H202 production that was associated with increased enzymatic activity of complex IV. From these results, we speculate that early exposure to hypoxia has long term, sex-dependent effects on cardiac metabolic function, which may have implications for cardiovascular health and disease in adulthood.