Desmoglein 2 mutation provokes skeletal muscle actin expression and accumulation at intercalated discs in murine hearts

Abstract

Arrhythmogenic cardiomyopathy (AC) is an incurable progressive disease that is linked to mutations in genes coding for components of desmosomal adhesions that are localized to the intercalated disc region, which electromechanically couples adjacent cardiomyocytes. To date, the underlying molecular dysfunctions are not well characterized. In two murine AC models, we find an upregulation of the skeletal muscle actin gene (Acta1), which is known to be a compensatory reaction to compromised heart function. Expression of this gene is elevated prior to visible morphological alterations and clinical symptoms, and persists throughout pathogenesis with an additional major rise during the chronic disease stage. We provide evidence that the increased Acta1 transcription is initiated through nuclear activation of the serum response transcription factor (SRF) by its transcriptional co-activator megakaryoblastic leukemia 1 protein (MKL1, also known as MRTFA). Our data further suggest that perturbed desmosomal adhesion causes Acta1 overexpression during the early stages of the disease, which is amplified by transforming growth factor β (TGFβ) release from fibrotic lesions and surrounding cardiomyocytes during later disease stages. These observations highlight a hitherto unknown molecular AC pathomechanism.

Inflammation shapes pathogenesis of murine arrhythmogenic cardiomyopathy

“…Similar phenomena are observed during the acute phase of Dsg2-related AC. Thus, the pro-inflammatory cytokines Tnfα and Il1β were detected together with the mRNA of the pro-fibrotic cytokines Lgals3 and, as previously described, also Tgfβ1 and Tgfβ3 [38]. T cells persist in the myocardial infarction and AC models.…”

“…The chronic nature of this response is reflected by the continued presence of macrophages, dendritic cells, and T cells in scar tissue. Furthermore, the previously reported connexin 43 redistribution in cardiomyocytes next to immune cell-enriched scars, alterations of actin distribution and actin isoform expression as well as pathological cardiomyocyte hypertrophy in murine Dsg2 mutants [31,38,39] are known to be induced by the macrophage-derived cytokines TNFα, IL1β, TGFβ and also CX3CL1 [24,27,28,36,47,66]. These cytokines are also likely involved in the formation of interstitial fibrosis that spreads from the established scars and may thereby contribute to the formation of arrhythmogenic substrates [27].…”

“…To better understand the pathomechanisms of AC and to explore possible therapies, multiple murine mouse models have been established [51]. To date, several mouse strains have been described that either overexpress mutant desmoglein 2 protein (denoted as DSG2) [52], lack DSG2 in cardiomyocytes [38] or constitutively produce mutant DSG2 [14,42] reflecting situations encountered in human AC patients ranging between homo-and heterozygosity and between mutant and absent DSG2 [17,18,58]. An AC-like phenotype was reported in all transgenic mouse lines presenting with cardiomyocyte death, inflammation, fibrosis, and cardiac dysfunction [40,42,52].…”

Arrhythmogenic Cardiomyopathy Is a Multicellular Disease Affecting Cardiac and Bone Marrow Mesenchymal Stromal Cells

“…Unbiased analysis of the total number of branches quantitated such qualitative alterations in the microtubular network, which appeared less branched in the AC cells ( Figure 3 c and Figure 4 c). Taken altogether, our results, by confirming previous evidence on the role of DSG2 in regulating cytoskeleton of different cell types [ 22 , 23 , 24 , 25 ], indicate that the primary Dsg2 mutation may affect the biology of both cardiac- and BM-MSCs.…”

“…At a first inspection with bright-field microscopy, we noticed that the AC mutant population included numerous grossly rounded and less frequent spindle-shaped cells, compared with controls, with a decrease in dimension. Based on the well-accepted role of the cytoskeletal dynamics and organization in determining cell shape, spreading, and stiffness, which eventually affect cell differentiation [ 22 ], and on the role of DSG2 in regulating actin assembly [ 23 , 24 , 25 ], cells were initially analyzed with confocal microscopy upon incubation with AlexaFLUOR ® -568 conjugated phalloidin (see Supplementary Methods ) to determine the distribution of intermediate filaments. Our analysis revealed that in the vast majority of Dsg2 mut/mut cells, the actin cytoskeleton—which in control cells, displayed an abundant number of thin, parallel microfilament bundles, extending across the entire cytoplasm—was dramatically different ( Figure 2 a–d).…”