Arrhythmogenic right ventricular cardiomyopathy (ARVC) is an inherited heart muscle disease, frequently accompanied by sudden cardiac death and terminal heart failure. Genotyping of ARVC patients might be used for palliative treatment of the affected family. We genotyped a cohort of 22 ARVC patients referred to molecular genetic screening in our heart center for mutations in the desmosomal candidate genes JUP, DSG2, DSC2, DSP and PKP2 known to be associated with ARVC. In 43% of the cohort, we found disease-associated sequence variants. In addition, we screened for desmin mutations and found a novel desmin-mutation p.N116S in a patient with ARVC and terminal heart failure, which is located in segment 1A of the desmin rod domain. The mutation leads to the aggresome formation in cardiac and skeletal muscle without signs of an overt clinical myopathy. Cardiac aggresomes appear to be prominent, especially in the right ventricle of the heart. Viscosimetry and atomic force microscopy of the desmin wild-type and N116S mutant isolated from recombinant Escherichia coli revealed severe impairment of the filament formation, which was supported by transfections in SW13 cells. Thus, the gene coding for desmin appears to be a novel ARVC gene, which should be included in molecular genetic screening of ARVC patients.

Background: Heterozygous DES mutations affect filament formation leading to skeletal and cardiomyopathies. Results: Our results reveal different extent of filament formation defects by various desmin mutants under heterozygous conditions. Conclusion: Analysis of interaction and co-localization of mutant and wild-type desmin proves the co-existence of heterogeneous filaments in living cells. Significance: These results might be of relevance for the understanding of filament formation defects.

In biological adhesion, the biophysical mechanism of specific biomolecular interaction can be divided in slip and catch bonds, respectively. Conceptually, slip bonds exhibit a reduced bond lifetime under increased external force and catch bonds, in contrast, exhibit an increased lifetime (for a certain force interval). Since 2003, a handful of biological systems have been identified to display catch bond properties. Upon investigating the specific interaction between the unique hydrophilic domain (HD) of the human cell-surface sulfatase Sulf1 against its physiological glycosaminoglycan (GAG) target heparan sulfate (HS) by single molecule force spectroscopy (SMFS), we found clear evidence of catch bond behavior in this system. The HD, ∼320 amino acids long with dominant positive charge, and its interaction with sulfated GAG-polymers were quantitatively investigated using atomic force microscopy (AFM) based force clamp spectroscopy (FCS) and dynamic force spectroscopy (DFS). In FCS experiments, we found that the catch bond character of HD against GAGs could be attributed to the GAG 6-O-sulfation site whereas only slip bond interaction can be observed in a GAG system where this site is explicitly lacking. We interpreted the binding data within the theoretical framework of a two state two path model, where two slip bonds are coupled forming a double-well interaction potential with an energy difference of ΔE ≈ 9 kBT and a compliance length of Δx ≈ 3.2 nm. Additional DFS experiments support this assumption and allow identification of these two coupled slip-bond states that behave consistently within the Kramers-Bell-Evans model of force-mediated dissociation.

The German family is not affected by a de novo TMEM43 mutation. It is therefore expected that an unknown number of European families may be affected by the TMEM43-p.S358L founder mutation. Due to its deleterious clinical phenotype, this mutation should be checked in any case of ARVC-related genotyping. It appears that the increased stiffness of the cell nucleus might be related to the massive loss of cardiomyocytes, which is typically found in ventricles of ARVC hearts.

T he intermediate filament (IF) protein desmin is encodedby the gene DES and contributes to the mechanical stabilization of the sarcomeres and cell contacts within the cardiac intercalated disk (ID). Desmin is the predominant IF protein of striated muscles. It belongs to the type III IF proteins characterized by a uniform assembly mechanism. In the first step of the in vitro assembly, 2 coiled-coil dimers form an antiparallel tetramer.1 These tetramers are the essential building blocks of the IF. Eight tetramers anneal in lateral orientation into unit length filaments. In the longitudinal elongation step, these unit length filaments are assembled and radially compacted into IF.2 Since the first reports on DES mutations, [3][4][5] it became obvious that DES mutations cause skeletal myopathies and different forms of cardiomyopathies. 6,7 Clinical Perspective on p 623In the meantime, >60 different DES mutations distributed over the whole sequence are known, which lead to filament formation defects with deposition of cytoplasmic desmin aggregates in the majority of cases. 8,9 However, the pathomechanisms of desmin aggregation leading to skeletal or cardiac myopathies are mechanistically not understood in detail. Moreover, 10-15 ARVC is an inherited cardiomyopathy clinically characterized by arrhythmias and predominately right ventricular dilatation leading to cardiac syncope, heart failure, or even sudden cardiac death (SCD). 16 It is well established that mutations in the genes coding for desmosomal plaque proteins cause ARVC [17][18][19] and rare forms of dilated cardiomyopathy. 20 In the cardiac muscle, desmin is found in costamers, the z-disk, and connected via plaque proteins to the cardiac desmosome within the ID. The molecular processes contributing to the destabilization of the ID through desmin filaments are fragmentarily understood. Especially, it is not known, how and which of the desmin mutations impair the connection of the IF system to the cardiac desmosome. Background-TheIn this study, we report a novel pathogenic DES mutation (c.359C>A, p.A120D), which seems to interfere particularly with the connection of desmin IF to the ID. Furthermore, we investigate whether the DES variants p.A120D and p.H326R (c.977A>G) affect the IF formation using ectopic expression cell culture systems and atomic force microscopy (AFM). These data reveal that desmin-p.A120D but not desmin-p. H326R inhibits the longitudinal assembly step, confirming its pathogenic potential. Materials and Methods Clinical Description of the PatientsIn family A, the 34-year-old female index patient (III:24) presented with atrial flutter, variable atrioventricular conduction ( Figure I in the online-only Data Supplement), and dilated atria. The average ventricular frequency was 64 bpm, and the atrial frequency was 120 bpm. In the ECG, some polymorphic premature ventricular contractions (PVCs) with a frequency of 45 to 111 bpm were detected ( Figure I in the online-only Data Supplement). The cardiological evaluation including 2-dimensional, M-m...