Susceptibility to Ventricular Arrhythmias Resulting from Mutations in FKBP1B, PXDNL, and SCN9A Evaluated in hiPSC Cardiomyocytes

Hector Barajas-Martinez; Maya Smith; Dan Hu; Robert J Goodrow; Colleen Puleo; Can Hasdemir; Charles Antzelevitch; Ryan Pfeiffer; Jacqueline A Treat; Jonathan M Cordeiro

doi:10.1155/2020/8842398

Susceptibility to Ventricular Arrhythmias Resulting from Mutations in FKBP1B, PXDNL, and SCN9A Evaluated in hiPSC Cardiomyocytes

Stem Cells Int. 2020 Sep 1:2020:8842398. doi: 10.1155/2020/8842398. eCollection 2020.

Authors

Hector Barajas-Martinez^{1

2}, Maya Smith¹, Dan Hu^{1

3}, Robert J Goodrow¹, Colleen Puleo¹, Can Hasdemir⁴, Charles Antzelevitch^{2

5}, Ryan Pfeiffer¹, Jacqueline A Treat¹, Jonathan M Cordeiro¹

Affiliations

¹ Department of Experimental Cardiology, Masonic Medical Research Institute, Utica, NY, USA.
² Department of Cardiovascular Research, Lakenau Institute for Medical Research, Wynnewood, PA, USA.
³ Department of Cardiology & Cardiovascular Research Institute, Renmin Hospital of Wuhan University, Wuhan, China.
⁴ Department of Cardiology, Ege University School of Medicine, Izmir, Turkey.
⁵ Kimmel College of Medicine of Thomas Jefferson University, Philadelphia, PA, USA.

Abstract

Background: We report an inherited cardiac arrhythmia syndrome consisting of Brugada and Early Repolarization Syndrome associated with variants in SCN9A, PXDNL, and FKBP1B. The proband inherited the 3 mutations and exhibited palpitations and arrhythmia-mediated syncope, whereas the parents and sister, who carried one or two of the mutations, were asymptomatic.

Methods and results: We assessed the functional impact of these mutations in induced pluripotent stem cell cardiomyocytes (hiPSC-CMs) derived from the proband and an unaffected family member. Current and voltage clamp recordings, as well as confocal microscopy analysis of Ca²⁺ transients, were evaluated in hiPSC-CMs from the proband and compared these results with hiPSC-CMs from undiseased controls. Genetic analysis using next-generation DNA sequencing revealed heterozygous mutations in SCN9A, PXDNL, and FKBP1B in the proband. The proband displayed right bundle branch block and exhibited episodes of syncope. The father carried a mutation in FKBP1B, whereas the mother and sister carried the SCN9A mutation. None of the 3 family members screened developed cardiac events. Action potential recordings from control hiPSC-CM showed spontaneous activity and a low upstroke velocity. In contrast, the hiPSC-CM from the proband showed irregular spontaneous activity. Confocal microscopy of the hiPSC-CM of the proband revealed low fluorescence intensity Ca²⁺ transients that were episodic in nature. Patch-clamp measurements in hiPSC-CM showed no difference in I _Na but reduced I _Ca in the proband compared with control. Coexpression of PXDNL-R391Q with SCN5A-WT displayed lower I _Na density compared to PXDNL-WT. In addition, coexpression of PXDNL-R391Q with KCND3-WT displayed significantly higher I _to density compared to PXDNL-WT.

Conclusion: SCN9A, PXDNL, and FKBP1B variants appeared to alter spontaneous activity in hiPSC-CM. Only the proband carrying all 3 mutations displayed the ERS/BrS phenotype, whereas one nor two mutations alone did not produce the clinical phenotype. Our results suggest a polygenic cause of the BrS/ERS arrhythmic phenotype due to mutations in these three gene variants caused a very significant loss of function of I _Na and I _Ca and gain of function of I _to.

Abstract

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