[K+]o-dependent change in conformation of the HERG1 long QT mutation N629D channel results in partial reversal of the in vitro disease phenotype

Abstract

This study reports a novel therapeutic strategy and mechanism to partially restore physiologic function in this HERG LQTS mutation.

Prolonged repolarization and triggered activity induced by adenoviral expression of HERG N629D in cardiomyocytes derived from stem cells

“…The characteristics of the endogenous I Kr currents in cardiac myocytes derived from stem cells are similar to that reported in freshly isolated fetal cardiac myocytes [15]. In adenoviral-N629D infected cardiac myocytes, three phenotypes similar to that reported during heterologous equimolar expression in Xenopus oocytes and mammalian cells [6,7] were observed. The mean current-voltage relationships for the time-dependent and the tail currents for the three current phenotypes are shown in Panels E and F (both n = 6), respectively.…”

“…Patients with the LQTS2 have a delayed repolarization phase, which predisposes to fatal arrhythmias. The N629D HERG mutation [5][6][7] is of particular interest as it alters the pore selectivity signature sequence GFGN (glycine -phenylalanine -glycine -asparagine) to GFGD (glycine -phenylalanine -glycine -aspartate). In contrast to wildtype (WT) HERG currents, homotetrameric N629D channels manifest outward rather than inward rectification and inward (Na + ) rather than outward (K + ) tail currents [6,7].…”

“…The N629D HERG mutation [5][6][7] is of particular interest as it alters the pore selectivity signature sequence GFGN (glycine -phenylalanine -glycine -asparagine) to GFGD (glycine -phenylalanine -glycine -aspartate). In contrast to wildtype (WT) HERG currents, homotetrameric N629D channels manifest outward rather than inward rectification and inward (Na + ) rather than outward (K + ) tail currents [6,7]. Since the LQTS is manifest in patients heterozygous for this trait, N629D and the wildtype constructs have been coexpressed at equimolar concentrations in Xenopus oocytes and in mammalian cells [7].…”

“…In contrast to wildtype (WT) HERG currents, homotetrameric N629D channels manifest outward rather than inward rectification and inward (Na + ) rather than outward (K + ) tail currents [6,7]. Since the LQTS is manifest in patients heterozygous for this trait, N629D and the wildtype constructs have been coexpressed at equimolar concentrations in Xenopus oocytes and in mammalian cells [7]. Such co-expression resulted in cells manifesting three different mutant I Kr phenotypes: (1) a WT-like phenotype (outward tail current and inward rectification), (2) a N629D-like phenotype (inward tail current and outward rectification) and (3) an intermediate phenotype (small outward tail current and minimal inward rectification [6]).…”

“…A common consequence was a variable loss of selectivity of the channel for K + over Na + , resulting in a positive shift in the reversal potential. Limitations of the previous studies [6,7] included the inability to assess whether such complex phenotypic variability was also manifest in cardiac myocytes and the inability to establish the physiologic relevance of the various phenotypes in cardiac myocytes. Accordingly, using adenoviral gene transfer, we overexpressed N629D in spontaneously beating cardiomyocytes derived from stem cells, which expressed endogenous HERG currents.…”