Mechanistic insights into arrhythmogenic right ventricular cardiomyopathy caused by desmocollin-2 mutations

Abstract

AimsRecent immunohistochemical studies observed the loss of plakoglobin (PG) from the intercalated disc (ID) as a hallmark of arrhythmogenic right ventricular cardiomyopathy (ARVC), suggesting a final common pathway for this disease. However, the underlying molecular processes are poorly understood.Methods and resultsWe have identified novel mutations in the desmosomal cadherin desmocollin 2 (DSC2 R203C, L229X, T275M, and G371fsX378). The two missense mutations (DSC2 R203C and T275M) have been functionally characterized, together with a previously reported frameshift variant (DSC2 A897fsX900), to examine their pathogenic potential towards PG's functions at the ID. The three mutant proteins were transiently expressed in various cellular systems and assayed for expression, processing, localization, and binding to other desmosomal components in comparison to wild-type DSC2a protein. The two missense mutations showed defects in proteolytic cleavage, a process which is required for the functional activation of mature cadherins. In both cases, this is thought to cause a reduction of functional DSC2 at the desmosomes in cardiac cells. In contrast, the frameshift variant was incorporated into cardiac desmosomes; however, it showed reduced binding to PG.ConclusionDespite different modes of action, for all three variants, the reduced ability to provide a ligand for PG at the desmosomes was observed. This is in agreement with the reduced intensity of PG at these structures observed in ARVC patients.

Molecular Insights into Arrhythmogenic Right Ventricular Cardiomyopathy Caused by Plakophilin-2 Missense Mutations

“…Previous reports have shown that in particular expression levels of JUP seem to be reduced in cardiac tissue from ARVC patients carrying mutations in desmosomal proteins. [14][15][16] However, our findings of unchanged expression levels are consistent in qualitative and quantitative immunofluorescence analyses of the endomyocardial biopsy, as well as in certain areas of the RV autopsy tissue ( Figures 1C and 2), but our investigations are limited to a specific missense mutation in PKP2 and tissue of 2 carriers, which will not allow us to generalize those findings. Interestingly, and in contrast to Asimaki et al, 14 our cardiac tissue samples came from 2 mutation carriers who showed only minor signs of disease, which might suggest that changes in the expression of desmosomal proteins develop with disease progression.…”

“…In contrast to mutations in other desmosomal components that have been shown to produce stable proteins, 3,15,16 in vitro studies in cardiac derived HL-1 cells indicate that mutations in ARM domains of PKP2 result in unstable proteins that undergo degradation (Figure 3; see online-only Data Supplement Figure III). Given that previous observations of N-terminally located PKP2 mutations (Q59L, Q62K, R79X) expressed in different cells have shown a similar mode of action, 17,18 we proposed that a simple cell culture model may help to decide whether a PKP2 variant is likely benign or pathogenic based on their in vitro expression pattern in HELAM2 cells.…”

“…4,14 Moreover, expression levels of other desmosomal proteins, in particular plakoglobin, have been suggested to be reduced in ARVC-related cardiac tissue. [14][15][16] In addition, cellular expression of 2 PKP2 nonsense mutations has produced unstable PKP2 proteins; 17,18 however, the process of protein degradation remains unclear. To date there are limited data about molecular and genetic mechanisms of missense mutations in the C-terminal armadillo domains, as well as their consequences in the context of human cardiac disease.…”

Different roles of cadherins in the assembly and structural integrity of the desmosome complex

“…For example, the intercalated discs that connect heart muscle cells contain one isoform of each subtype (Dsc2 and Dsg2) (Delva et al, 2009), and mutations in Dsc2 and Dsg2 cause hereditary diseases such as arrhythmogenic right ventricular cardiomyopathy (ARVC) (Bhuiyan et al, 2009;Heuser et al, 2006) and mild striate palmoplantar keratoderma (SPPK) ). Several of these hereditary mutations have been mapped to the extracellular domain of Dsg2 and Dsc2 (Gaertner et al, 2012;Gehmlich et al, 2011). In the epidermis, different Dsg and Dsc isoforms are expressed in a cell-typespecific manner, and autoimmune diseases such as pemphigus foliaceus and pemphigus vulgaris target extracellular binding of Dsg1 and Dsg3, causing loss of adhesion in the epidermis and mucosal membranes (Amagai and Stanley, 2012;Waschke, 2008).…”

Familial Evaluation for Diagnosis of Arrhythmogenic Right Ventricular Dysplasia

“…Several studies of patients with ARVD have revealed multiple pathologic mutations in DSC2 with a frequency ranging from 0 to 7% [8,9,10,11,15,16]. Desmocollin-2 is a desmosomal transmembrane protein and the exclusive desmocollin isoform expressed in cardiac tissue [1,6].…”