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BACKGROUND: Arrhythmogenic cardiomyopathy (ACM) is one of the leading causes of sudden cardiac death in children, young adults, and athletes and is characterized by the fibro-fatty replacement of the myocardium, predominantly of the right ventricle. Sixty percent of patients with ACM have a known genetic cause, but for the remainder, the etiology is unknown. This lack of mechanistic understanding has also slowed the development of disease-modifying therapies, and children with ACM have a high degree of morbidity and mortality.
METHODS: Induced pluripotent stem cells (iPSCs) from 3 family members were differentiated into cardiac myocytes (CMs). Calcium imaging was conducted by labeling calcium with CAL-520 and confocal imaging to capture calcium sparks after iPSC-CMs were electrically paced. A cardiac-specific, inducible knockout mouse (Tax1bp3-/-) was made and intracardiac electrophysiology studies conducted to observe arrhythmia inducibility following pacing.
RESULTS: We identified a kindred with multiple members affected by ACM cosegregating with biallelic variants in the gene TAX1BP3, which encodes the protein TAX1BP3 (Tax1-binding protein 3). iPSC-CMs derived from this kindred demonstrated increased intracellular lipid droplets, induction of TRPV4 (transient receptor potential vanilloid type 4) expression, and inducible TRPV4 current. This was associated with depletion of the intracellular sarcoplasmic reticulum Ca2+ store and increased RyR2 (ryanodine receptor 2)-mediated store Ca2+ leak and delayed afterdepolarizations, a known mechanism of Ca2+-mediated arrhythmogenesis. Similarly, Tax1bp3 cardiac-specific knockout mice had increased Ca2+ leak and were predisposed to ventricular arrhythmias compared with wild-type mice. Ca2+ leak in both the iPSC-CMs and mouse ventricular myocytes was rescued by small molecule TRPV4 inhibition. This strategy also effectively reduced Ca2+ leak in a PKP2 (plakophilin 2) p.His773AlafsX8 iPSC-CM model of ACM.
CONCLUSIONS: We conclude that TAX1BP3 is associated with rare autosomal recessive ACM through TRPV4-mediated Ca2+ leak from RyR2. Further, TRPV4 current inhibition has the potential to be a new therapeutic target for ACM.
