Abstracts

Rationale: hERG1_NP, encoded by KCNH2, is a polypeptide expressed in the nuclei of developing cardiomyocytes and neurons. KCNH2 variants that map to hERG1_NP are linked with both sudden infant death syndrome (SIDS) and sudden unexplained death in epilepsy (SUDEP), but the mechanism(s) by which hERG1_NP variants promote sudden death and epilepsy are unknown. We previously demonstrated that hERG1_NP nuclear targeting modulates gene expression, leading to reduced potassium current at the cell surface membrane. Here, we measured the impact of two hERG1_NP variants associated with sudden death on hERG1_NP function, R1047L and Q1068R. R1047L was identified in four distinct cases of SUDEP, whereas Q1068R was identified in a case of SIDS. Both R1047L and Q1068R map to the hERG1_NP coiled-coil domain, the only confirmed secondary structure in the hERG1_NP polypeptide.


Methods: To determine the basic effects of R1047L and Q1068R on hERG1_NP activity we expressed either GFP, hERG1_NP-wildtype, hERG1_NP-R1047L, or hERG1_NP-Q1068R in HEK293 cells. We quantified intracellular trafficking using confocal microscopy and measured surface membrane potassium currents by patch clamp.


Results: Consistent with our previous work, wildtype hERG1_NP was targeted almost exclusively to the cell nuclei and it reduced potassium current magnitude at the surface membrane by roughly half, compared to GFP-transfected controls. R1047L abolished both hERG1_NP nuclear trafficking as well as modulation of membrane potassium currents. In contrast, Q1068R did not affect nuclear targeting but displayed enhanced the inhibition of potassium current magnitude, compared to wildtype hERG1_NP. A third KCNH2 variant, G965A, which does not map to the hERG1_NP coiled-coil domain and is not associated with sudden death, did not alter hERG1_NP activity.


Conclusions: This work demonstrates that biochemistry of the hERG1_NP coiled-coil domain is critically important for normal hERG1_NP function. Collectively, these data demonstrate that R1047L and Q1068R have opposing effects on hERG1_NP activity. Thus, this work suggests two distinct mechanisms by which hERG1_NP variants could alter neuronal function. Follow up work in a more clinically translational experimental paradigm is needed to further outline these potential disease mechanisms.


Funding: American SIDS Institute
University of Michigan Frankel Cardiovascular Center McKay Grant