Protein quality control pathways as modifiers of disease severity in PLN cardiomyopathy

Abstract

Phospholamban (PLN) cardiomyopathy is a genetic heart disease caused by mutation in PLN gene, which results in protein aggregates formation and disrupted calcium homeostasis in cardiomyocytes, leading to progressive cardiac dysfunction. PLN cardiomyopathies are characterized by substantial heterogeneity in clinical presentation and disease severity, even among patients carrying the same pathogenic variant (PLN-R14del). The mechanisms underlying these differences remain incompletely understood. We hypothesized that variability in the activity of protein quality control systems contributes to differential disease severity by modulating the handling of misfolded and aggregated proteins in cardiomyocytes.

To address this, we analyzed plasma samples from patients with confirmed mutation displaying variable clinical phenotypes. Protein-level analyses performed on peripheral blood samples revealed differences in the expression of genes involved in protein homeostasis, including pathways related to deubiquitination, proteosomal degradation and endoplasmic reticulum (ER) stress responses. These findings were complemented by studies in patient-derived induced pluripotent stem cell–derived cardiomyocytes (iPSC-CMs) obtained from patients susceptible vs. resilient to cardiomyopathy development. The cells recapitulated key molecular features observed in patient samples.

Specifically, the imaging approaches demonstrated the presence of PLN protein aggregates in PLN-R14del iPSC-CMs in contrast to control cardiomyocytes, while the bigger and more numerous aggregates were observed in the susceptible group. Moreover, in iPSC-CMs, we detected genotype- and phenotype-dependent differences in mRNA and protein expression of components of the ubiquitin–proteasome system and autophagy machinery. Our data suggest that the autophagy is properly initiated in susceptible PLN-R14del iPSC-CMs, but completion of the degradation process is impaired, leading to proteostatic stress, accumulation of protein aggregates and contributing to disease progression.

Together, our results suggest that the PLN cardiomyopathy severity may be influenced by inter-individual differences in the efficiency of protein aggregate clearance pathways. These data highlight protein quality control systems as potential modifiers of disease phenotype and suggest that therapeutic strategies aimed at modulating deubiquitination, autophagy, or ER stress responses could represent promising avenues for future intervention in selected patient subgroups.