Abstract 12290: The African-American Single Nucleotide Polymorphism (snp) Rs34423165 in Ldb3 Alters Kv7.1 in Familial Dcm with Qt-Prolongation
Background: Genetic mutations in the LDB3-encoding the Z-band alternatively spliced PDZ motif-containing protein (ZASP) cause cardiomyopathy associated with arrhythmias and sudden cardiac death (SCD), although the underlying mechanism remains unclear. We have previously identified the common SNP rs34423165 (p.K251R in NM_001080115.1; p.K204R in NM_001080114.1) in a patient with significant family history of QT-prolongation and SCD associated with dilated cardiomyopathy (DCM). We hypothesized that rs34423165 may affect cardiac repolarization and specifically the delayed rectifier K+ channel.
Methods and Results: The proband is an 18-year old female presenting with QT-prolongation (QTc = 510 ms) associated with mild LV dilatation. Three of six first relatives were affected, and two of them (father and uncle) died suddenly. The effects of ZASP4-K251R on the delayed rectifier K+ currents were studied using whole-cell mode of patch-clamp techniques. CHO cells expressing Kv7.1 and KCNE1 (IKs), Kv11.1 and KCNE2 (IKr), or Nav1.5 (INa) were transfected with ZASP4-wt or ZASP4-K251R. The macroscopic IKs induced with a step-pulse protocols were significantly reduced in the cells transfected with ZASP4-K251R compared to ZASP4-wt (IKs-tail at -120 mV: K251R, -76.4 ± 7.5 pA/pF, n = 8; WT, -150.5 ± 33.1 pA/pF, n = 7, p<0.01). Surprisingly, ZASP4-K251R decreased IK even without KCNE1, which was reported to be a physical adaptor between Kv7.1 and ZASP4. Interestingly, when we use the NM_001080114.1 isoform (ZASP1) lacking the PKC-binding LIM domains as template, ZASP1- K204R also decreased IKs (IKs-tail at -120 mV: K204R, -42.3 ± 31.6 pA/pF, n = 5; WT, -166.2 ± 23.9 pA/pF, n = 7, p<0.01). Co-immunoprecipitation study demonstrated that both ZASP4-wt and ZASP4-K251R physically interact with Kv7.1. On the contrary, ZASP4-K251R did not affect the steady-state activation of IKr (IKr-steady at 0 mV: K251R, 2.54 ± 0.3 pA/pF, n = 6; WT, 2.19 ± 0.3 pA/pF, n = 8, NS.) and INa (peak INa: K251R, -257.8 ± 56.5 pA/pF, n = 8; WT, -250.9 ± 21.4 pA/pF, n = 8, NS.)
Conclusion: Our study suggests that the common African American LDB3 SNP rs34423165 causes loss-of-function of Kv7.1 via a direct ZASP/ Kv7.1 protein-protein interaction, thus conferring susceptibility to QT-prolongation and SCD.
- © 2011 by American Heart Association, Inc.