Summary The Cancer Genome Atlas (TCGA) project has analyzed mRNA expression, miRNA expression, promoter methylation, and DNA copy number in 489 high-grade serous ovarian adenocarcinomas (HGS-OvCa) and the DNA sequences of exons from coding genes in 316 of these tumors. These results show that HGS-OvCa is characterized by TP53 mutations in almost all tumors (96%); low prevalence but statistically recurrent somatic mutations in 9 additional genes including NF1, BRCA1, BRCA2, RB1, and CDK12; 113 significant focal DNA copy number aberrations; and promoter methylation events involving 168 genes. Analyses delineated four ovarian cancer transcriptional subtypes, three miRNA subtypes, four promoter methylation subtypes, a transcriptional signature associated with survival duration and shed new light on the impact on survival of tumors with BRCA1/2 and CCNE1 aberrations. Pathway analyses suggested that homologous recombination is defective in about half of tumors, and that Notch and FOXM1 signaling are involved in serous ovarian cancer pathophysiology.

Bayer AG.

Rationale Beta-adrenergic receptor (β-AR) stimulation produces sarcoplasmic reticulum (SR) Ca2+ overload and delayed after-depolarizations (DADs) in isolated ventricular myocytes. How DADs are synchronized to overcome the source-sink mismatch and produce focal arrhythmia in the intact heart remains unknown. Objective To determine if local β-AR stimulation produces spatio-temporal synchronization of DADs and to examine the effects of tissue geometry and cell-cell coupling on the induction of focal arrhythmia. Methods and Results Simultaneous optical mapping of transmembrane potential (Vm) and Ca2+ transients (CaT) was performed in normal rabbit hearts during subepicardial injections (50µL) of norepinephrine (NE) or control (normal Tyrodes). Local NE produced premature ventricular complexes (PVCs) from the injection site, which were dose-dependent (low-dose [30–60µM]: 0.45±0.62 vs. high-dose [125–250µM]: 1.33±1.46 PVCs/injection, p<0.0001) and were inhibited by propranolol. NE-induced PVCs exhibited abnormal Vm-Ca2+ delay at the initiation site, and were inhibited by either SERCA inhibition or reduced perfusate [Ca2+], indicating a Ca2+-mediated mechanism. NE-induced PVCs were more common at RV vs. LV sites (1.48±1.50 vs. 0.55±0.89, p<0.01) which was unchanged following chemical ablation of endocardial Purkinje fibers, suggesting source-sink interactions may contribute to the greater propensity to RV PVCs. Partial gap junction uncoupling with carbenoxolone (25µM) increased focal activity (2.18±1.43 vs. 1.33±1.46 PVCs/injection, p<0.05), further supporting source-sink balance as a critical mediator of Ca2+-induced PVCs. Conclusions These data provide the first experimental demonstration that localized β-AR stimulation produces spatio-temporal synchronization of SR Ca2+ overload and release in the intact heart and highlight the critical nature of source-sink balance in initiating focal arrhythmias.

Rationale Sarcoplasmic reticulum (SR) Ca2+ cycling is key to normal excitation-contraction coupling but may also contribute to pathological cardiac alternans and arrhythmia. Objective To measure intra-SR free [Ca2+] ([Ca2+]SR) changes in intact hearts during alternans and ventricular fibrillation (VF). Methods and Results Simultaneous optical mapping of Vm (with RH237) and [Ca2+]SR (with Fluo-5N AM) was performed in Langendorff-perfused rabbit hearts. Alternans and VF were induced by rapid pacing. SR Ca2+ and action potential duration (APD) alternans occurred in-phase, but SR Ca2+ alternans emerged first as cycle length was progressively reduced (217±10ms vs. 190±13ms, p<0.05). Ryanodine receptor (RyR) refractoriness played a key role in the onset of SR Ca2+ alternans, with SR Ca2+ release alternans routinely occurring without changes in diastolic [Ca2+]SR. Sensitizing RyR with caffeine (200μM) significantly reduced the pacing threshold for both SR Ca2+ and APD alternans (188±15ms and 173±12ms, p<0.05 vs. baseline). Caffeine also reduced the magnitude of spatially discordant SR Ca2+ alternans, but not APD alternans, the pacing threshold for discordance, or threshold for VF. During VF, [Ca2+]SR was high, but RyR remained nearly continuously refractory, resulting in minimal SR Ca2+ release throughout VF. Conclusions In intact hearts RyR refractoriness initiates SR Ca2+ release alternans, that can be amplified by diastolic [Ca2+]SR alternans and lead to APD alternans. Sensitizing RyR suppresses spatially concordant, but not discordant SR Ca2+ and APD alternans. Despite increased [Ca2+]SR during VF, SR Ca2+ release was nearly continuously refractory. This novel method provides insight into SR Ca2+ handling during cardiac alternans and arrhythmia.

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