Desmosomal protein degradation as an underlying cause of arrhythmogenic cardiomyopathy.

Arrhythmogenic cardiomyopathy (ACM) is an inherited progressive cardiac disease. Many patients with ACM harbor mutations in desmosomal genes, predominantly in plakophilin-2 (PKP2). Although the genetic basis of ACM is well characterized, the underlying disease-driving mechanisms remain unresolved. Explanted hearts from patients with ACM had less PKP2 compared with healthy hearts, which correlated with reduced expression of desmosomal and adherens junction (AJ) proteins. These proteins were also disorganized in areas of fibrotic remodeling. In vitro data from human-induced pluripotent stem cell-derived cardiomyocytes and microtissues carrying the heterozygous PKP2 c.2013delC pathogenic mutation also displayed impaired contractility. Knockin mice carrying the equivalent heterozygous Pkp2 c.1755delA mutation recapitulated changes in desmosomal and AJ proteins and displayed cardiac dysfunction and fibrosis with age. Global proteomics analysis of 4-month-old heterozygous Pkp2 c.1755delA hearts indicated involvement of the ubiquitin-proteasome system (UPS) in ACM pathogenesis. Inhibition of the UPS in mutant mice increased area composita proteins and improved calcium dynamics in isolated cardiomyocytes. Additional proteomics analyses identified lysine ubiquitination sites on the desmosomal proteins, which were more ubiquitinated in mutant mice. In summary, we show that a plakophilin-2 mutation can lead to decreased desmosomal and AJ protein expression through a UPS-dependent mechanism, which preceded cardiac remodeling. These findings suggest that targeting protein degradation and improving desmosomal protein stability may be a potential therapeutic strategy for the treatment of ACM.

CRISPR Craze to Transform Cardiac Biology.

Clustered regularly interspaced short palindromic repeats (CRISPR) has revolutionized many research areas and has rapidly become the gold standard in genome editing by outrivaling all other available tools. Its unprecedented versatility creates the opportunity to modify any aspect of gene regulation. Even though the cardiac field is starting to appreciate the potential of CRISPR, many applications to study cardiac biology and disease so far have remained untouched. In particular, CRISPR-based strategies that act independent of the homology-directed repair pathway could help circumvent issues of modifying the genome of postmitotic cardiomyocytes, which is currently limiting its utility in the heart. Here, we review current applications and future potential for the use of CRISPR to study cardiac biology and disease.