Loss of function (LOF) variants in KCNQ1 or KCNH2, encoding KV7.1 and KV11.1 respectively, are the commonest causes of the congenital long QT syndrome (LQTS). Previous studies have suggested that a KV7.1-KV11.1 interaction can modulate KV11.1 cell surface expression and thus determine whether a KCNQ1 LOF variant generates a severe phenotype.
To define mechanisms whereby haploinsufficient (HI) KCNQ1 variants can nevertheless generate a severe LQTS phenotype.
We studied induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) from a patient with Jervell Lange-Nielsen syndrome (JLN) caused by biallelic LOF variants of KCNQ1: R518X (known to cause nonsense-mediated mRNA decay) and an exon6 skipping splicing variant (ex6skip). IKr and IKs were compared in JLN cells before and after R518X was corrected by genome editing, and to control cells. We also generated stable HEK293 lines expressing both wild-type KCNH2 and KCNQ1 wild-type, ex6skip, or one of 5 HI clinically highly penetrant KCNQ1 variants: F340del, A341V, T587M, R591H, R594Q. We quantified KV11.1 surface abundance by flow cytometry and assessed KV7.1-KV11.1 interactions by co-immunoprecipitation (co-IP).
JLN iPSC-CMs showed prolonged action potentials and near total loss of IKs. In edited cells carrying only ex6skip, IKs was significantly increased (0.1±0.03 pA/pF to 1.3±0.3 pA/pF [mean±S.E.] at 40 mV) compared to control (0.9±0.4 pA/pF), but IKr was significantly decreased (1.9±0.2 to 0.2±0.1 pA/pF at 20 mV; control =1.4±0.2 pA/pF). In HEK293 co-IP experiments, F340del, A341V, and ex6skip produced no KV7.1 and no KV11.1 binding while the other variants (R591H, T587M, R594Q) did generate KV7.1 which interacted with KV11.1. Despite these differences, all 6 variants decreased KV11.1 surface abundance, by 8-22%, compared to wild-type.
Penetrant HI variants decrease KV11.1 surface abundance through multiple mechanisms. These data reinforce the importance of assessing not only IKs alone but also IKr as mediators of disease severity in LQTS.
© 2021 Published by Elsevier Inc.