P62-positive aggregates are homogenously distributed in the myocardium and associated with the type of mutation in genetic cardiomyopathy.

Zoë Joy Klooster,Frederique S A M Schuiringa,Johannes Peter Tintelen,Wouter P Te Rijdt,Folkert W Asselbergs,Jolanthe Lingeman,Albert J H Suurmeijer,Roel Goldschmeding,Shahrzad Sepehrkhouy,Dennis Dooijes,Magdalena Harakalova,Aryan Vink

doi:10.1111/jcmm.16388

Abstract

Genetic cardiomyopathy is caused by mutations in various genes. The accumulation of potentially proteotoxic mutant protein aggregates due to insufficient autophagy is a possible mechanism of disease development. The objective of this study was to investigate the distribution in the myocardium of such aggregates in relation to specific pathogenic genetic mutations in cardiomyopathy hearts. Hearts from 32 genetic cardiomyopathy patients, 4 non‐genetic cardiomyopathy patients and 5 controls were studied. Microscopic slices from an entire midventricular heart slice were stained for p62 (sequestosome‐1, marker for aggregated proteins destined for autophagy). The percentage of cardiomyocytes with p62 accumulation was higher in cardiomyopathy hearts (median 3.3%) than in healthy controls (0.3%; P < .0001). p62 accumulation was highest in the desmin (15.6%) and phospholamban (7.2%) groups. P62 accumulation was homogeneously distributed in the myocardium. Fibrosis was not associated with p62 accumulation in subgroup analysis of phospholamban hearts. In conclusion, accumulation of p62‐positive protein aggregates is homogeneously distributed in the myocardium independently of fibrosis distribution and associated with desmin and phospholamban cardiomyopathy. Proteotoxic protein accumulation is a diffuse process in the myocardium while a more localized second hit, such as local strain during exercise, might determine whether this leads to regional myocyte decay.

Highlights

We investigated the presence of p62 proteotoxic aggregates in genetic cardiomyopathies caused by pathogenic mutations in different cardiomyopathy-related genes (DES, CRYAB, PLN, PKP2, DSP, lamin A/C (LMNA), MYBPC3, MYH7, TNNI3 and TNNT2)
For p62 quantification, the heart slice was divided into five regions for the free wall of the left ventricle (LV; anterior, anterolateral, lateral, posterolateral and posterior), one region for the septum and two regions for the right ventricle (RV; posterior and anterior) as we have described previously (Figure 1).[8,9]
We show that proteotoxic stress in phospholamban cardiomyopathy is present in a relatively large percentage of cardiomyocytes in the myocardium as compared to most other genetic cardiomyopathies

Summary

Introduction

In hearts of cardiomyopathy patients with a pathogenic variant in the gene encoding phospholamban (PLN), we have recently demonstrated aggregates that are both p62 and phospholamban positive.[5] This suggests that the autophagy system is not able to remove all the mutant phospholamban protein, resulting in accumulation of p62- positive proteotoxic perinuclear aggregates in the cardiomyocytes. In the whole group of cardiomyopathy hearts, no significant differences were observed between the percentage of p62-positive cells in the RV (2.3% [0.9-4.9]), septum (3.1% [1.5-6.8]) and LV (3.6%[1.4- 6.4]).

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Results

Conclusion