MTMR4 SNVs modulate ion channel degradation and clinical severity in congenital long QT syndrome: insights in the mechanism of action of protective modifier genes

• Published in: Cardiovascular research 2021-02, Vol.117 (3), p.767-779
• Main Authors: Lee, Yee-Ki, Sala, Luca, Mura, Manuela, Rocchetti, Marcella, Pedrazzini, Matteo, Ran, Xinru, Mak, Timothy S H, Crotti, Lia, Sham, Pak C, Torre, Eleonora, Zaza, Antonio, Schwartz, Peter J, Tse, Hung-Fat, Gnecchi, Massimiliano
• Format: Article
• Language: English
• Subjects: Cells, Cultured; Genes, Modifier; Genetic Predisposition to Disease; Humans; Induced Pluripotent Stem Cells - metabolism; KCNQ1 Potassium Channel - genetics; KCNQ1 Potassium Channel - metabolism; Long QT Syndrome - genetics; Long QT Syndrome - metabolism; Mutation; Myocytes, Cardiac - metabolism; Nedd4 Ubiquitin Protein Ligases - genetics; Nedd4 Ubiquitin Protein Ligases - metabolism; Original; Phenotype; Polymorphism, Single Nucleotide; Protein Tyrosine Phosphatases, Non-Receptor - genetics; Protein Tyrosine Phosphatases, Non-Receptor - metabolism; Proteolysis
• ISSN: 0008-6363; 1755-3245
• DOI: 10.1093/cvr/cvaa019

Abstract Aims In long QT syndrome (LQTS) patients, modifier genes modulate the arrhythmic risk associated with a disease-causing mutation. Their recognition can improve risk stratification and clinical management, but their discovery represents a challenge. We tested whether a cellular-driven approach could help to identify new modifier genes and especially their mechanism of action. Methods and results We generated human-induced pluripotent stem cell-derived cardiomyocytes (iPSC-CM) from two patients carrying the same KCNQ1-Y111C mutation, but presenting opposite clinical phenotypes. We showed that the phenotype of the iPSC-CMs derived from the symptomatic patient is due to impaired trafficking and increased degradation of the mutant KCNQ1 and wild-type human ether-a-go-go-related gene. In the iPSC-CMs of the asymptomatic (AS) patient, the activity of an E3 ubiquitin-protein ligase (Nedd4L) involved in channel protein degradation was reduced and resulted in a decreased arrhythmogenic substrate. Two single-nucleotide variants (SNVs) on the Myotubularin-related protein 4 (MTMR4) gene, an interactor of Nedd4L, were identified by whole-exome sequencing as potential contributors to decreased Nedd4L activity. Correction of these SNVs by CRISPR/Cas9 unmasked the LQTS phenotype in AS cells. Importantly, the same MTMR4 variants were present in 77% of AS Y111C mutation carriers of a separate cohort. Thus, genetically mediated interference with Nedd4L activation seems associated with protective effects. Conclusion Our finding represents the first demonstration of the cellular mechanism of action of a protective modifier gene in LQTS. It provides new clues for advanced risk stratification and paves the way for the design of new therapies targeting this specific molecular pathway.