Molecular basis for clinical heterogeneity in inherited cardiomyopathies due to myopalladin mutations

Abstract

Abnormalities in Z-disc proteins cause hypertrophic (HCM), dilated (DCM) and/or restrictive cardiomyopathy (RCM), but disease-causing mechanisms are not fully understood. Myopalladin (MYPN) is a Z-disc protein expressed in striated muscle and functions as a structural, signaling and gene expression regulating molecule in response to muscle stress. MYPN was genetically screened in 900 patients with HCM, DCM and RCM, and disease-causing mechanisms were investigated using comparative immunohistochemical analysis of the patient myocardium and neonatal rat cardiomyocytes expressing mutant MYPN. Cardiac-restricted transgenic (Tg) mice were generated and protein-protein interactions were evaluated. Two nonsense and 13 missense MYPN variants were identified in subjects with DCM, HCM and RCM with the average cardiomyopathy prevalence of 1.66%. Functional studies were performed on two variants (Q529X and Y20C) associated with variable clinical phenotypes. Humans carrying the Y20C-MYPN variant developed HCM or DCM, whereas Q529X-MYPN was found in familial RCM. Disturbed myofibrillogenesis with disruption of α-actinin2, desmin and cardiac ankyrin repeat protein (CARP) was evident in rat cardiomyocytes expressing MYPN(Q529X). Cardiac-restricted MYPN(Y20C) Tg mice developed HCM and disrupted intercalated discs, with disturbed expression of desmin, desmoplakin, connexin43 and vinculin being evident. Failed nuclear translocation and reduced binding of Y20C-MYPN to CARP were demonstrated using in vitro and in vivo systems. MYPN mutations cause various forms of cardiomyopathy via different protein-protein interactions. Q529X-MYPN causes RCM via disturbed myofibrillogenesis, whereas Y20C-MYPN perturbs MYPN nuclear shuttling and leads to abnormal assembly of terminal Z-disc within the cardiac transitional junction and intercalated disc.

Novel mutations in the sarcomeric protein myopalladin in patients with dilated cardiomyopathy

“…Moreover, transgenic mice with cardiac-restricted overexpression of p.Y20C mutant showed disrupted intercalated disks and developed hypertrophic cardiomyopathy. 15 It would provide strong evidence for the pathological role of the MYPN mutations identified in our study if knock-in mouse models with the corresponding substitution mutations of the homologous amino acids were to develop DCM.…”

“…3 Recently, four other point mutations have been detected exclusively in DCM patients (p.I213V, p.Y339F, p.A611T, and p.A882T), and only one of these mutations (p.Y339F) was predicted as damaging. 15 The p.Y20C variant reported by these authors was not restricted to DCM patients as it was also found in a patient with hypertrophic cardiomyopathy. Moreover, transgenic mice with cardiac-restricted overexpression of p.Y20C mutant showed disrupted intercalated disks and developed hypertrophic cardiomyopathy.…”

“…As a number of missense mutations in genes encoding for titin and titin-associated proteins have recently been reported to be responsible for DCM, 3,[12][13][14][15][19][20][21][22][23][24][25] we searched in a well-characterized sample of DCM patients for unknown SNPs and/or mutations in the human MYPN and ANKRD1 genes. In order to extend our knowledge on disease-causing mutations in these two proteins expressed in heart tissue, we screened the coding sequences and corresponding intron flanks of the two genes and found two novel non-synonymous mutations in the MYPN gene and only one rare synonymous SNP in the coding region of the ANKRD1 gene.…”

“…11 Recently, mutations in the myopalladin-encoding MYPN and the CARP-encoding ANKRD1 gene (also termed ankyrin-repeat domain 1-encoded cardiac adriamycin responsive protein) have been reported in patients with DCM. 3,[12][13][14][15] As titin-binding proteins have been proposed to link mechanical load sensing in sarcomeres to myocardial gene expression, we extended the search for novel point mutations in a heterogeneous, but clinically well-characterized cohort of familial and sporadic DCM cases. Based on a mutational screening approach, we here present additional genetic variants identified in the two titinassociated proteins, which were thought to be most probably disease causing.…”

Recent Developments in the Genetics of Cardiomyopathies

“…Zebrafish models have, however, been used to demonstrate the role of BAG3 mutations in DCM [28]. Another alternative is to use mouse models [34,35]. A recent functional study in mice demonstrated that certain mutations in MYPN may result in disturbed myofibrillogenesis or disrupted intercalated discs leading to various forms of cardiomyopathy, including HCM and RCM [35].…”