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

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.

Infanticide vs. inherited cardiac arrhythmias

“…Recently a mechanism of action of a protective modifier gene has been described for LQTS: the family members carrying this protective variant, which compensates the loss of potassium current produced by the disease-causing mutation, had a completely normal ECG and QT interval. 34 …”

Human mesenchymal stromal cells do not express ACE2 and TMPRSS2 and are not permissive to SARS-CoV-2 infection

“…SARS‐CoV‐2 spike pseudotyped retroviral particles were produced by cotransfection of 293T cells (ThermoFisher) with these following three plasmids: a replication‐deficient retroviral vector FCQ pMM2‐eGFP expressing the green fluorescent protein (GFP) 20 ; a packaging vector pUMVC (#8449 Addgene), and an envelope vector 2019‐nCoV Spike ORF mammalian expression plasmid (VG40589‐UT Sino Biologicals), or pCMV‐VSV‐G (#8454 Addgene) expressing the vesicular stomatitis virus glycoprotein (VSV‐G) as a positive control. MSCs were incubated with Spike or VSV‐G pseudotyped viral particles for 24 hours.…”

Use of hiPSC-derived cardiomyocytes to rule out proarrhythmic effects of drugs: the case of hydroxychloroquine in COVID-19

“…A strategy to identify patients at risk of developing drug-induced QT prolongation and arrhythmias is still lacking, but there is a strong need for valid models which reproduce or predict the genotype-specific consequences of drugs on silent cLQTS mutation carriers; this would be particularly relevant for individuals with borderline QT intervals whose pathogenic variants often go undiagnosed in routine ECGs but which may significantly increase the arrhythmogenic susceptibility to QT prolonging drugs. This also applies for individuals carrying variants in protective/detrimental genetic modifiers (Itoh et al, 2016;Chai et al, 2018;Lee et al, 2021). Despite the promising in vitro results, HCQ did not confirm its efficacy in vivo neither in preventing SARS-CoV-2 infection nor in treating the severe consequences of the infection, with findings confirmed by several independent studies (Graham et al, 2020;Axfors et al, 2021;Jorge, 2021;Macías et al, 2021;Rentsch et al, 2021;WHO Solidarity Trial Consortium et al, 2021).…”

“…One was affected by the CALM1-p.F142L variant (Crotti et al, 2013) associated with CALM-LQTS, which manifests in infants, is extremely severe, and responds poorly to therapy (Rocchetti et al, 2017;Crotti et al, 2019). hiPSCs from healthy subjects: one was an unrelated bona fide healthy donor (WT (Lee et al, 2021) while hiPSCs from the second donor (WT2) were provided by the Coriell Institute for Medical Research (WTC-11 line, catalog No. GM25256).…”