Early consequences of the phospholamban mutation PLN-R14del^+/− in a transgenic mouse model

Aims: The heterozygous phospholamban (PLN) mutation R14del (PLN R14del^+/−) is associated with a severe arrhythmogenic cardiomyopathy (ACM) developing in the adult. “Superinhibition” of SERCA2a by PLN R14del is widely assumed to underlie the pathogenesis, but alternative mechanisms such abnormal energy metabolism have also been reported. This work aims to (1) to evaluate Ca²⁺ dynamics and energy metabolism in a transgenic (TG) mouse model of the mutation prior to cardiomyopathy development; (2) to test whether they are causally connected. Methods: Ca²⁺ dynamics, energy metabolism parameters, reporters of mitochondrial integrity, energy, and redox homeostasis were measured in ventricular myocytes of 8–12 weeks-old, phenotypically silent, TG mice. Mutation effects were compared to pharmacological PLN antagonism and analyzed during modulation of sarcoplasmic reticulum (SR) and cytosolic Ca²⁺ compartments. Transcripts and proteins of relevant signaling pathways were evaluated. Results: The mutation was characterized by hyperdynamic Ca²⁺ handling, compatible with a loss of SERCA2a inhibition by PLN. All components of energy metabolism were depressed; myocyte energy charge was preserved under quiescence but reduced during stimulation. Cytosolic Ca²⁺ buffering or SERCA2a blockade reduced O₂ consumption with larger effect in the mutant. Signaling changes suggest cellular adaptation to perturbed Ca²⁺ dynamics and response to stress. Conclusions: (1) PLN R14del^+/− loses its ability to inhibit SERCA2a, which argues against SERCA2a superinhibition as a pathogenetic mechanism; (2) depressed energy metabolism, its enhanced dependency on Ca²⁺ and activation of signaling responses point to an early involvement of metabolic stress in the pathogenesis of this ACM model.