BPS2026 – Designer peptide modulators of sodium channels attenuate CaMKII-dependent arrhythmias

Voltage-gated sodium channels are essential for cardiac electrical activity, and their dysfunction contributes to the development of arrhythmias. Sodium channel function is critically modulated by intracellular regulatory proteins, including calmodulin (CaM), Ca/CaM-dependent protein kinase II (CaMKII), and intracellular fibroblast growth factor homologous factors (FHFs). In heart failure (HF), the late sodium current (I Na,Late ) is markedly enhanced and contributes to arrhythmogenic action potentials (APs). CaMKII is upregulated in HF, and its transgenic overexpression (CaMKII-TG) induces eccentric cardiac hypertrophy, HF, and arrhythmias. We tested antiarrhythmic effects of two newly designed modulatory peptides of I Na,Late in CaMKII-TG mice: the FHF1 A -mimicking N-terminal 39-aa FHF inhibiting x region (FixR) and the engineered late-current inhibitor X by inactivation-gate release (ELIXIR), a de novo AI-designed peptide. Cell pretreatment with the tat-conjugated cell-penetrating peptide (cpp) versions of FixR and ELIXIR in CaMKII-TG ventricular myocytes significantly inhibited the enhanced I Na,Late and attenuated proarrhythmogenic AP changes (AP duration prolongation, increased beat-to-beat variability, heightened alternans susceptibility) and delayed afterdepolarizations (DADs). We also tested for in vivo FixR effects via adenoviral delivery in CaMKII-TG. FixR significantly reduced QT prolongation on ECG and decreased in vivo arrhythmia susceptibility in CaMKII-TG mice. In healthy controls, FixR and ELIXIR had minimal effect on physiological I Na,Late and did not significantly alter any AP or ECG parameters. In conclusion, FixR and ELIXIR are selective for I Na,Late and have potent antiarrhythmic properties, highlighting the potential of rational protein design in engineering synthetic ion channel modulators for the treatment of cardiac arrhythmias.