Abstract Body (Do not enter title and authors here): Background TANGO2 deficiency disease (TDD), caused by a homozygous large deletion in the Tango2 gene, is associated with impaired fatty acid oxidation-triggered metabolic crises, which can include severe QT prolongation and ventricular arrhythmias. The mechanism of transient QT prolongation and arrhythmias is unknown. Here we test the hypothesis that activation of the nonselective cation channel TRPM4, regulated by intracellular ATP and Ca, contributes mechanistically to arrhythmia risk in TDD.

Methods CRISPR/Cas9 was used to generate a human induced pluripotent stem cell cardiomyocyte (hiPSC-CM) model with a Tango2 exon 3 to 9 deletion (Tango2^-/-). Mitochondrial oxygen consumption rate (OCR), intracellular ATP/ADP ratios, and action potentials (APs) were evaluated in Tango2^-/- hiPSC-CMs under metabolic conditions fueled by either 5.6 mmol/L glucose or 0.1 mmol/L palmitate.

Results Analogous to clinical TDD, Tango2^-/- hiPSC-CMs showed a significant decrease in palmitate-dependent OCR and a profound reduction in intracellular ATP production when palmitate was the sole substrate, worsened after 24-hour fasting. In contrast, when glucose was the only energy source, Tango2^-/- hiPSC-CMs demonstrated OCR and ATP production rates comparable to control. These observations suggest dysfunction in mitochondrial palmitate oxidation leading to energy deficiency in Tango2^-/- hiPSC-CMs, which subsequently result in prolongation of AP duration. Intracellular delivery of Mg-ATP normalized palmitate-induced AP prolongation in Tango2^-/- hiPSC-CMs post fasting. Additionally, although no alterations in L-type Ca current were found, L-type Ca channel inhibition with verapamil alleviated palmitate-induced AP prolongation in Tango2^-/- hiPSC-CMs post fasting by stabilizing ATP/ADP ratios and ameliorating intracellular calcium dysregulation. We found post-fasting exposure to palmitate upregulated Trpm4 gene expression in Tango2^-/- hiPSC-CMs. Targeted genetic knockdown or pharmacological blockade of TRPM4 channels normalized AP prolongation in Tango2^-/- hiPSC-CMs.

Conclusion Our findings established a mechanistic link between myocardial energy deficiency, TRPM4 activation and the development of AP prolongation in TDD, emphasizing the energetic basis of arrhythmias. Targeting TRPM4 is a promising new therapeutic strategy to prevent QT prolongation and arrhythmia in TDD.