Increased L-type calcium current causes action potential prolongation in Jervell and Lange-Nielsen syndrome and is a drug target.

Abstract

Background: KCNQ1 loss of function variants are thought to cause type 1 long QT syndrome by reducing I _Ks . However, we have recently reported that pharmacologic block of I _Ks in human induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) produced minimal increases in action potential duration at 90% repolarization (APD ₉₀ ), while genetic loss of KCNQ1 markedly prolonged APD ₉₀ . We sought here to define mechanisms underlying APD prolongation by genetic loss of KCNQ1 .

Methods: We studied iPSC-CMs from population controls, an isogenic KCNQ1 knock out (KO) line created by a homozygous edit for the R518X loss of function variant, and 2 unrelated patients with the Jervell and Lange-Nielsen syndrome (JLN) due to compound heterozygosity for loss of function KCNQ1 variants.

Results: In both JLN and the KCNQ1-KO lines, I _Ks was absent, APD ₉₀ was markedly prolonged, and L-type Ca channel (LTCC) current ( I _Ca-L ) was significantly increased, 2-3-fold, compared to the control cells with no change in kinetics or gating. RNA-sequencing identified 298 and 584 genes that were up- and down-regulated, respectively, by KCNQ1-KO compared to the isogenic control cells. Gene ontology analysis identified down-regulation of 6 Ca ²⁺ channel negative regulatory genes (p=0.0002, FDR=0.02), and in knockdown experiments in wild-type iPSC-CMs, three of these, CBARP , FKBP1B , and RRAD , increased I _Ca-L , and RRAD increased APD ₉₀ . A therapeutic low concentration (1 μM) of the Ca channel antagonist diltiazem significantly shortened APD ₉₀ in the two JLN cell lines and in KCNQ1-KO cells. A single low dose of intravenous diltiazem in one of the JLN patients shortened QTc.

Conclusions: These data further support the concept that delayed repolarization in JLN cannot be explained solely by loss of I _Ks . Our findings demonstrate that KCNQ1 mutations lead to down-regulation of Ca ²⁺ channel inhibitory genes, with resultant increased I _Ca-L that underlies delayed repolarization in JLN. We further propose that diltiazem can be repurposed for treatment of patients with JLN.