Sillje, H. H. W. | Search bioRxiv

bioRxiv2024

Unbiased complexome profiling and global proteomics analysis reveals mitochondrial impairment and potential changes at the intercalated disk in presymptomatic R14Delta/+ mice hearts

BackgroundPhospholamban (PLN) is a sarco-endoplasmic reticulum (SER) membrane protein that regulates cardiac contraction/relaxation by reversibly inhibiting the SERCA2a Ca2+-reuptake pump. The R14{Delta}-PLN mutation causes severe cardiomyopathy that is resistant to conventional treatment. Protein complexes and higher-order supercomplexes such as intercalated disk components and Ca+2-cycling domains underlie many critical cardiac functions, a subset of which may be disrupted by R14{Delta}-PLN. MethodsWe developed an improved complexome profiling (CP) workflow specifically geared towards identifying disruption of very high molecular-weight (>2 MDa) protein complexes and supercomplexes in presymptomatic R14{Delta}/+ mice hearts. Ventricular tissues were homogenized under non-denaturing conditions, fractionated by size-exclusion chromatography (SEC) and subjected to quantitative data-independent acquisition mass spectrometry (DIA-MS) proteomics analysis. Systematic analysis of CP data using conventional strategies yielded limited insights, likely due to underrepresentation of cardiac-specific complexes in the curated protein complex databases used as ground-truth for analysis. We thus developed PERCOM: a novel data analysis strategy that does not rely upon protein complex databases and can, furthermore, be implemented on widely available spreadsheet software. ResultsSEC-DIA-MS coupled with PERCOM identified 296 proteins with disrupted elution profiles in presymptomatic 28wk-old R14{Delta}/+ mice. Hits were significantly enriched for mitochondrial and intercalated disk (ICD) components. Alterations to mitochondrial and ICD supercomplexes were observed in mice as young as 9wks of age and were associated with reduced expression of mitochondrial proteins and maximal oxygen consumption rate. ConclusionUsing a novel CP workflow, we identify mitochondrial alterations as an early-stage R14{Delta}-PLN event and provide preliminary data showing effects at the ICD. These molecular components underlie critical cardiac functions and their alteration at a young age may contribute to R14{Delta}-PLN pathogenesis.

cell biology↗

bioRxiv2023

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

AimsThe 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 and ResultsCa2+ 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 analysed during modulation of sarcoplasmic reticulum (SR) and cytosolic Ca2+ compartments. Transcripts and proteins of relevant signalling pathways were evaluated. The mutation was characterized by hyperdynamic Ca2+ handling, similar to that induced by PLN antagonism. Albeit all components of energy metabolism were depressed at rest, functional signs of mitochondrial damage or energy starvation were absent and cell energy charge was preserved. The response of mitochondrial O2 consumption to SERCA2a blockade was lost in mutant myocytes (SR-mitochondrial uncoupling) and ER-stress signalling was activated. Conclusions1) PLN R14del+/- loses its ability to inhibit SERCA2a, which argues against SERCA2a superinhibition as a mechanism of ACM; 2) depression of resting energy metabolism may at least partly reflect impairment of SR-mitochondrial coupling; 3) ER-stress may be an early factor in the pathogenesis.

physiology↗