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Early consequences of the phospholamban mutation PLN-R14del+/- in a transgenic mouse model
Claudia Maniezzi1, Marem Eskandr1, Chiara Florindi1
1Department of Biotechnology and Bioscience, University of Milano-Bicocca, Milan, Italy.
Insights
The phospholamban (PLN) R14del mutation causes arrhythmogenic cardiomyopathy by disrupting calcium handling and energy metabolism, not by SERCA2a superinhibition. Early metabolic stress and signaling changes are key to this condition.
Area of Science:
- Cardiology
- Molecular Biology
- Biochemistry
Background:
- The heterozygous phospholamban (PLN) R14del mutation is linked to severe arrhythmogenic cardiomyopathy (ACM).
- Pathogenesis is often attributed to "superinhibition" of SERCA2a, but altered energy metabolism is also implicated.
Purpose of the Study:
- Evaluate Ca2+ dynamics and energy metabolism in a pre-clinical mouse model of PLN R14del.
- Investigate the causal link between these factors and ACM development.
Main Methods:
- Assessed Ca2+ handling, energy metabolism, mitochondrial integrity, and redox homeostasis in ventricular myocytes of young, asymptomatic transgenic mice.
- Compared mutation effects with pharmacological PLN antagonism and modulated Ca2+ compartments.
- Analyzed relevant signaling pathways at transcript and protein levels.
Main Results:
- PLN R14del myocytes exhibited hyperdynamic Ca2+ handling, suggesting a loss of SERCA2a inhibition.
- Energy metabolism was depressed, with reduced energy charge during stimulation.
- Cellular responses indicated adaptation to perturbed Ca2+ dynamics and stress.
Conclusions:
- The PLN R14del mutation impairs SERCA2a inhibition, challenging the superinhibition hypothesis.
- Depressed energy metabolism, Ca2+ dependency, and signaling activation suggest early metabolic stress in ACM pathogenesis.
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.
