Metabolic crisis and TRPM4 activation cause QT prolongation in TANGO2 deficiency disorder

Lili Wang; Kyungsoo Kim; Prince J Kannankeril; Chen Zheng; Daniel J Blackwell; Samuel J Mackenzie; Paul S Brookes; Björn C Knollmann

doi:10.1093/cvr/cvag143

. 2026 Jul 2;122(12):1626–1641. doi: 10.1093/cvr/cvag143

Metabolic crisis and TRPM4 activation cause QT prolongation in TANGO2 deficiency disorder

Lili Wang ^1,^✉,², Kyungsoo Kim ², Prince J Kannankeril ³, Chen Zheng ⁴, Daniel J Blackwell ⁵, Samuel J Mackenzie ⁶, Paul S Brookes ⁷, Björn C Knollmann ^8,^✉,²

PMCID: PMC13508696 PMID: 42389941

Abstract

Aims

TANGO2 deficiency disorder (TDD), caused by biallelic pathogenic variants in TANGO2, is associated with impaired fatty acid oxidation and metabolic crises that frequently trigger QT prolongation and arrhythmias. The objective was to study the mechanisms responsible for QT prolongation and arrhythmogenesis in TDD.

Methods and results

CRISPR/Cas9 were used to generate human-induced pluripotent stem cell cardiomyocytes (hiPSC-CMs) carrying a TANGO2 exon 3–9 deletion (TANGO2^−/−). Bioenergetic function (mitochondrial oxygen consumption rate, intracellular ATP/ADP ratio) and action potentials (APs) were studied under glucose- or palmitate-fueled conditions. This study reports a TDD clinical case of QT prolongation and arrhythmia that responded favourably to L-type calcium channel (LTCC) inhibition with verapamil or vitamin B-complex supplementation. The mechanisms underlying clinical presentations and therapeutic responses were investigated using TANGO2^−/− hiPSC-CMs. In glucose-containing medium, the bioenergetic function was comparable between control and TANGO2^−/− hiPSC-CMs. In contrast, using palmitate as energy substrate triggered a profound reduction in cellular ATP production rate and decreased ATP/ADP ratios in TANGO2^−/− hiPSC-CMs, exacerbated by 24-h fasting. This crisis was prevented by 2-week treatment with vitamins B5 and B9. During the crisis, TANGO2^−/− hiPSC-CMs exhibited AP prolongation, prevented by intracellular delivery of Mg-ATP or creatine kinase. LTCC inhibition with verapamil prevented AP prolongation by normalizing ATP/ADP ratios and intracellular Ca mishandling. Importantly, the metabolic crisis upregulated TRPM4, an ATP- and Ca-regulated channel. TRPM4 siRNA knockdown or pharmacological block prevented AP prolongation without rescuing the energetic deficit of TANGO2^−/− hiPSC-CMs.

Conclusion

These findings suggest a mechanistic link between ATP deficiency, TRPM4 activation, and AP prolongation in TDD. Targeting TRPM4 therapeutically may help prevent QT prolongation and cardiac arrhythmias in TDD crisis.

Keywords: TDD, hiPSC-CMs, ATP deficiency, Cardiac arrhythmia, Intracellular Ca mishandling, TRPM4

Graphical Abstract

In the clinical case study, a patient with TANGO2 deficiency disorder shows severe QT prolongation and ventricular arrhythmia. After treatment with verapamil or vitamin B complex supplementation, the QT interval normalizes and the arrhythami resolves. In the cellular mechanism, control and CRISPR/Cas9-generated TANGO2-knockout hiPSCs are differentiated into cardiomyocytes. In TANGO2-deficient cardiomyocytes, impaired palmitate oxidation causes energy deficiency and intracellular calcium mishandling, which increase TRPM4, prolong the action potential, and trigger arrhythmia. Vitamin B5 and B9 rescue the upstream palmitate oxidation defect, verapamil corrects the ATP deficiency, and TRPM4 acts as a key mediator of the eletrical abnormality.

Time of primary review: 32 days

1. Introduction

Transport and Golgi organization 2 (TANGO2), encoded by the TANGO2 gene, plays a crucial role in intracellular trafficking and mitochondrial morphology and function.^1–3 Pathogenic variants in TANGO2, most commonly a deletion of Exons 3–9, lead to TANGO2 deficiency disorder (TDD), a rare autosomal recessive condition. TDD is characterized by episodic metabolic crises and cardiac arrhythmias, often triggered by illness or fasting.^4,5 During metabolic crises, TDD patients exhibit a constellation of symptoms, including hypoglycaemia, lactic acidosis, elevated serum creatine kinase levels, and variably abnormal plasma acylcarnitine profiles.^4,6 These symptoms collectively implicate metabolic dysfunction, namely impaired long-chain fatty acid oxidation, in the pathophysiology of TDD. Notably, these crises are frequently accompanied by transient electrocardiogram changes, particularly QT prolongation and ventricular arrhythmias.⁷ However, the mechanistic link between metabolic crises and cardiac electrical instability in TDD remains poorly understood.

TRPM4 (transient receptor potential melastatin subfamily member 4), a non-selective cation channel robustly expressed in the human heart, has been implicated in Ca-triggered arrhythmia.⁸ TRPM4 can modulate action potential (AP) repolarization through its inward rectifying properties, which allows inward Na current at negative membrane potential.⁹ Importantly, TRPM4 activity is regulated by two factors disrupted during metabolic crisis: The channel is activated by Ca elevation and energy imbalance.^10,11 This dual sensitivity makes TRPM4 a potential ‘metabolic sensor’ positioned to translate cellular ATP deficiency into electrical instability, possibly explaining the mechanistic link between metabolic dysfunction and arrhythmogenesis in TDD.

To investigate the mechanism underlying arrhythmia in TDD, we used human-induced pluripotent stem cell cardiomyocytes (hiPSC-CMs). hiPSC-CMs have become valuable experimental models in vitro due to their human origin and ability to recapitulate the cellular phenotypes of cardiac diseases.^12,13 However, their structural and functional immaturity can limit their accuracy. To address this limitation, we employed an advanced maturation protocol using triiodothyronine (T3) and dexamethasone (Dex) during cardiac differentiation. This approach enhances the development of functional T-tubules and improves the electrophysiological maturation of hiPSC-CMs,^14,15 increasing their fidelity in modelling cardiac diseases in vitro.

Here, we report a TDD clinical case of life-threatening ventricular arrhythmias that responded acutely to verapamil, an L-type calcium channel (LTCC) blocker, and were prevented long-term by vitamin B-complex supplementation. To elucidate the mechanisms underlying arrhythmogenesis and the therapeutic response to verapamil, we developed a hiPSC-CM model of TDD and demonstrate that TANGO2 deficiency specifically impairs palmitate oxidation, creating an ATP deficiency that activates TRPM4 and prolongs action potential duration (APD). Critically, either ATP restoration or TRPM4 inhibition prevented arrhythmia phenotypes, while vitamin B5/B9 supplementation corrected the underlying metabolic defect. These findings establish TRPM4 as the mechanistic link between metabolic dysfunction and electrical abnormalities in TDD, identifying it as a novel therapeutic target for preventing cardiac arrhythmias during metabolic crises.

2. Methods

This study was conducted in accordance with the principles outlined in accordance with the Declaration of Helsinki and was approved by the Vanderbilt University Medical Center Institutional Review Board (protocol # 090544). hiPSCs were derived from dermal fibroblasts obtained from a healthy volunteer who provided written informed consent. The source, generation, and characterization of control hiPSCs have been previously described in Wang et al.¹⁶ Detailed methods are provided in the Supplementary material online.

2.1. Statistical analysis

Experiments were performed using hiPSC-CMs from three independent cardiac differentiations. Normality was examined using the Shapiro–Wilk test before applying the appropriate statistical test. Data were transformed as needed to achieve normal distribution prior to statistical analysis. To account for batch-to-batch cardiac differentiation variation and quality, statistical analyses were performed using a hierarchical statistical model with Bonferroni correction in R, following the procedures outlined in Sikkel et al.¹⁷ Figures were prepared using GraphPad Prism version 9.0 (GraphPad Software). Representative images/traces were selected from records that had values close to the mean/median measure. Detailed statistical information, including sample sizes and significance levels, is provided in the corresponding figure legends. Exact P values for all group comparisons are summarized in Supplementary material online, Table S7.

3. Results

3.1. TDD: a clinical case study

A therapeutic response to verapamil was noted in a 6-year-old boy with TDD secondary to biallelic exon 3-to-9 deletions in the TANGO2 gene. His case has been included in multicentre series^18,19 and a report documenting the effectiveness of left stellate ganglion blockade.²⁰ During his first hospitalization after cardiac arrest, prior to establishing his TDD diagnosis, the patient presented with refractory ventricular arrhythmias secondary to severe QT prolongation, resistant to multiple antiarrhythmic medications including esmolol, lidocaine, and amiodarone.^18,19 He required venoarterial extracorporeal membrane oxygenation (ECMO) support and left stellate ganglion block appeared effective.²⁰ Surgical left cardiac sympathetic denervation was performed on hospital day (HD) #5 on IV esmolol. On HD #8, he was removed from ECMO and transitioned from esmolol to nadolol with predominantly sinus rhythm. On HD #15, he had recurrent runs of torsades de pointes, with no improvement despite trials of IV lidocaine and isoproterenol. A single dose of verapamil (2 mg IV) led to immediate suppression of ectopy and loss of T-wave alternans (Figure 1). A repeat dose was similarly effective, and IV verapamil drip was started. He was eventually transitioned to oral verapamil for discharge, and a single chamber ICD was placed. He has subsequently done relatively well on oral verapamil, with recurrent ICD shocks only during metabolic crises at times of decreased absorption of verapamil secondary to ileus. At age 9 years, he started on vitamin B-complex supplementation, inclusive of vitamin B5 (pantothenic acid, 100 mg/day) and vitamin B9 (folate, 800 µg/day), based on retrospective clinical data and studies in model systems of TDD.^21–24 Verapamil was discontinued at age 11 years. In the 2 years following the initiation of vitamin B-complex supplementation, the patient has not experienced recurrent metabolic crises or cardiac arrhythmia.

For image description, please refer to the figure legend and surrounding text — Continuous telemetry over 12 min showing sinus rhythm with macroscopic T-wave alternans and episodes of torsades de pointes (TdP). After IV verapamil, there is marked normalization of repolarization and sinus rhythm with no ventricular ectopy or arrhythmias. Red boxes are magnified images of macroscopic T-wave alternans, TdP, and sinus rhythm with normal QT immediately after verapamil.

3.2. Development of TANGO2^−/− hiPSC model

We used a dual-sgRNA CRISPR/Cas9 strategy to delete the TANGO2 Exons 3–9 and generate TANGO2 knockout (TANGO2^−/−) hiPSCs (see Supplementary material online, Figure S1A). After screening multiple edited hiPSC colonies, we identified two clonal lines, designated TANGO2^−/− L1 and L2, that harboured the biallelic TANGO2 Exons 3–9 deletion (see Supplementary material online, Figure S1B). Western blot analysis confirmed the complete absence of TANGO2 protein in cardiomyocytes (CMs) differentiated from TANGO2^−/− L1 and L2 hiPSC lines (see Supplementary material online, Figure S1D). Both TANGO2^−/− hiPSC lines were studied and compared to an isogenic control line in all experiments.

3.3. Cellular bioenergetic function

Previous studies suggest that TDD patients have impaired long-chain fatty acid oxidation during metabolic crisis.^4,25 We examined this phenomenon in TANGO2^−/− hiPSC-CMs using palmitate, a prevalent circulating long-chain fatty acid. When treated with 0.1 mmol/L palmitate as the sole metabolic substrate, TANGO2^−/− hiPSC-CMs showed significantly reduced intracellular ATP/ADP ratios compared to control (Figure 2A), indicating ATP deficiency. Seahorse XF analysis revealed significantly reduced palmitate-dependent basal oxygen consumption rate (OCR) and ATP-linked OCR in TANGO2^−/− hiPSC-CMs (Figure 2B–D). The TANGO2^−/− cells exhibited decreased ATP production from mitochondrial oxidative phosphorylation (OXPHOS) without compensatory increases in glycolytic ATP (see Supplementary material online, Figure S2), resulting in overall reduced ATP production rate (Figure 2E). Importantly, glucose metabolism remained intact: exposure to 5.6 mmol/L glucose did not alter ATP/ADP ratios (Figure 2A), OCR (see Supplementary material online, Figure S3B), or ATP production rate (see Supplementary material online, Figure S3C) in TANGO2^−/− hiPSC-CMs compared to control. This substrate-specific defect- impaired palmitate oxidation with preserved glucose oxidation mirrors clinical observations in TDD patients.⁴

To investigate metabolic substrate preference, we performed a Seahorse assay using a combination of glucose (5.6 mmol/L) and palmitate (0.1 mmol/L) in the extracellular media (Figure 2F). TANGO2^−/− hiPSC-CMs exhibited significantly lower baseline OCR compared to control (Figure 2G). Application of 0.1 mmol/L etomoxir to block palmitate oxidation reduced OCR to similar levels in both groups, confirming that the baseline difference stemmed from impaired palmitate oxidation in TANGO2^−/− hiPSC-CMs. The greater etomoxir-induced OCR reduction in control vs. TANGO2^−/− hiPSC-CMs (Figure 2G) confirmed that T3 + Dex-treated hiPSC-CMs preferentially utilize palmitate for ATP production.

We next examined how hiPSC-CMs respond to fasting, which triggers metabolic reprogramming and increases the reliance on fatty acid metabolism in cardiomyocytes during periods of low glucose availability.^26,27 After a 24-h fasting period (culturing cells in substrate-free medium), control hiPSC-CMs showed increased palmitate-dependent basal OCR and ATP-linked OCR when exposed to 0.1 mmol/L palmitate (Figure 2B–D). This enhanced mitochondrial ATP production while decreasing glycolysis-derived ATP (see Supplementary material online, Figure S2), thereby maintaining overall ATP production rate (Figure 2E). Conversely, TANGO2^−/− hiPSC-CMs exhibited further decreased ATP/ADP ratios post-fasting (Figure 2A), with reduced ATP production rate despite unchanged palmitate-dependent basal OCR (Figure 2C) and mitochondrial ATP production (see Supplementary material online, Figure S2). Neither metabolic condition altered OXPHOS complex protein expression in either cell type (see Supplementary material online, Figure S4).

RNA sequencing revealed substrate-dependent transcription changes in TANGO2^−/− hiPSC-CMs (see Supplementary material online, Figure S5). Under glucose conditions, 13 genes were upregulated and 56 downregulated; under palmitate exposure following 24-h fasting, and 19 genes were upregulated and 46 downregulated. DAVID functional annotation analysis revealed that glucose activated hormone signalling pathways (hsa04081) while suppressing protease binding (GO:0002020) and glycoprotein annotation (KW-0325). Post-fasting palmitate exposure produced minimal pathway activation, affecting only signal peptide processing (KW-0732) and presynaptic membrane components (GO:0042734). Zinc finger transcription factors were consistently downregulated in TANGO2^−/− hiPSC-CMs across both metabolic conditions, indicating fundamental transcriptional disruption (see Supplementary material online, Figure S5). Notably, CPT1B (the rate-limiting enzyme for fatty acid entry into mitochondria) increased in TANGO2^−/− hiPSC-CMs under both conditions (see Supplementary material online, Figure S6), suggesting compensatory upregulation of palmitate transport to mitochondria in response to impaired fatty acid oxidation. Although TANGO2 deficiency impaired palmitate oxidation, it did not disrupt cardiac development or maturation. RNA sequencing analysis revealed that genes essential for cardiac structure and function remained unchanged under both glucose and palmitate conditions. Cardiac contractile genes (MYH7, MYH6, TNNI3, TNNI1) maintained normal expression, as did critical ion channel genes (SCN5A, CACNA1C, HCN4, KCNJ2, KCNJ12, KCNH2, KCNQ1, KCNE2, GJA1), Ca handling proteins (ATP2A2, RYR2, PLN), and mitochondrial genes (TOMM20, PPARGC1A, PPARA, ATP5F1A, UQCRC2, SDHB, COX2, NDUFB8) (see Supplementary material online, Figure S6). This preservation of cardiac development and function genes demonstrates that TANGO2 deficiency specifically impairs the fatty acid oxidation, while leaving intact the fundamental developmental programmes that establish cardiac structure and function capacity. This selective substrate-specific defect explains why TANGO2-deficient cardiomyocytes develop normally but fail only when metabolic stress demands fatty acid oxidation.

3.4. Synergistic vitamin B5/B9 treatment and palmitate oxidation

To recapitulate the clinical benefits of vitamin B supplementation, we treated control and TANGO2^−/− hiPSC-CMs with vitamin B5 (0.05 mmol/L), B9 (0.05 mmol/L), or a combination of both (0.025 mmol/L each) for 2 weeks. In the combination treatment, we reduced each vitamin's concentration to half of their individual doses to maintain equivalent total vitamin concentration across all treatment groups, enabling us to distinguish between synergistic interactions from simple additive effects.

Following a 24-h fast, the B5/B9 combination treatment significantly increased palmitate-dependent OCR in both control and TANGO2^−/− hiPSC-CMs, with a markedly greater effect in TANGO2^−/− cells (see Supplementary material online, Figure S7A and B). In TANGO2^−/− hiPSC-CMs, the combination treatment substantially enhanced both palmitate-dependent OCR and ATP production rate compared to either vitamin alone (see Supplementary material online, Figure S7B and C), thus increasing intracellular ATP/ADP ratios and effectively correcting the ATP deficiency (see Supplementary material online, Figure S7D). In control hiPSC-CMs, vitamin B9 alone showed modest efficacy on palmitate-dependent OCR, while vitamin B5 alone had no significant effect (see Supplementary material online, Figure S7A–C). Nevertheless, the B5/B9 combination demonstrated superior enhancement of post-fasting palmitate oxidation even in control hiPSC-CMs. Importantly, neither individual vitamin nor the B5/B9 combination altered OXPHOS complex protein expression in either cell type (see Supplementary material online, Figure S8). These findings support the clinical efficacy of vitamin B-complex supplementation in TDD patients and highlight the synergistic effect of combining vitamins B5 and B9 in addressing TDD-specific metabolic deficits.

3.5. Metabolic substrate-dependent electrical regulation

Previous studies have demonstrated the impact of altered metabolic function on cardiac electrophysiology.²⁸ Given palmitate's influence on ATP production rate and intracellular ATP/ADP ratios in TANGO2^−/− hiPSC-CMs, we investigated its effect on cardiac electrical activity. We measured extracellular field potentials (EFPs) in control and TANGO2^−/− hiPSC-CMs monolayers at 1-Hz pacing under three conditions: 5.6 mmol/L glucose, 0.1 mmol/L palmitate, and 0.1 mmol/L palmitate following 24-h fasting. Figure 3A–C displays representative metabolic substrate-dependent EFP traces recorded in control and TANGO2^−/− hiPSC-CM monolayers. We quantified multiple EFP parameters using semi-automated EFP analyzer software as previously described²⁹: Field potential upstroke duration termed QRS duration, total field potential duration (FPD), field potential repolarization amplitude termed T-wave amplitude (TampA, measured as baseline-to-peak voltage during repolarization), beat-to-beat variation in TampA (TampA alternans), and FPD (FPD alternans). QRS duration remained unchanged between genotypes across all metabolic conditions, confirming preserved depolarization (Figure 3D). In glucose-containing media, there were no differences in FPD and TampA between groups. In contrast, palmitate exposure significantly prolonged FPD in TANGO2^−/− monolayers, an effect that was further exacerbated post-fasting (Figure 3G). Notably, TampA increased significantly in TANGO2^−/− monolayers exclusively under post-fasting palmitate conditions (Figure 3E), reflecting enhanced spatial dispersion of repolarization. Electrical instability was unmasked progressively through alternans patterns: FPD alternans emerged under palmitate exposure and worsened post-fasting (Figure 3H), while TampA alternans appeared exclusively during severe ATP deficiency under post-fasting palmitate conditions (Figure 3F)

FPD is determined by both single-cell AP characteristics and cellular conduction velocity. Given that the expression of GJA1 (encoding connexin 43) remained unchanged between groups across both glucose and palmitate conditions according to RNA-seq results (see Supplementary material online, Figure S6), we reasoned that altered cellular APs were the primary driver of FPD prolongation and FPD alternans in TANGO2^−/− hiPSC-CMs. Hence, we measured single-cell APs using patch clamp. Figure 4A displays representative AP traces from control and TANGO2^−/− hiPSC-CMs paced at 0.5 Hz under three conditions: 5.6 mmol/L glucose, 0.1 mmol/L palmitate, or 0.1 mmol/L palmitate following 24-h fasting. Figure 4B and Supplementary material online, Figure S9A and B demonstrate AP alternans under these same conditions. Consistent with the EFP results (Figure 3), 5.6 mmol/L glucose exposure produced similar APD between control and TANGO2^−/− hiPSC-CMs, while 0.1 mmol/L palmitate exposure significantly prolonged APD₉₀ (Figure 4C) and increased AP alternans (Figure 4D) in TANGO2^−/− hiPSC-CMs. Following a 24-h fasting, palmitate exposure resulted in considerably longer APD₉₀ and increased AP alternans in TANGO2^−/− hiPSC-CMs (Figure 4C and D). Other AP parameters (see Supplementary material online, Table S1) such as AP overshoot (between 0 mV and the peak), resting membrane potential, and maximal upstroke velocity (V_max) remained comparable between groups, indicating that the prolongation of APD was specifically related to repolarization abnormalities rather than depolarization defects.

To test whether post-fasting palmitate-induced energetic deficit (i.e. decreased ATP/ADP ratio) causes APD prolongation in TANGO2^−/− hiPSC-CMs, we sustained intracellular ATP levels by adding creatine kinase (2.5 units) and phosphocreatine (PCr) (2 mmol/L) to the pipette solution during AP measurements. This approach enabled creatine kinase to facilitate phosphate transfer from PCr to ADP,³⁰ maintaining adequate ATP levels within TANGO2^−/− hiPSC-CMs. Representative AP and AP alternans traces are shown in Figure 5A and Supplementary material online, Figure S9C. The intracellular infusion of creatine kinase and PCr prevented palmitate-induced APD₉₀ prolongation (Figure 5B) and AP alternans (Figure 5C) in TANGO2^−/− hiPSC-CMs, indicating an ATP-dependent arrhythmia mechanism. To further probe this mechanism, we directly introduced 10 mmol/L Mg-ATP (the primary cytosolic ATP form in cardiomyocytes) into the pipette solution and measured APs in TANGO2^−/− hiPSC-CMs after 24-h fasting with 0.1 mmol/L palmitate exposure. Representative traces are shown in Supplementary material online, Figure S10A and B. We observed no significant differences in APD₉₀ (see Supplementary material online, Figure S10C) or AP alternans (see Supplementary material online, Figure S10D) between control and TANGO2^−/− hiPSC-CMs, reinforcing the ATP-dependent mechanism underlying arrhythmic phenotypes in TDD. AP parameters are summarized in Supplementary material online, Table S3.

Verapamil, a non-dihydropyridine LTCC blocker, prevented QT prolongation and arrhythmia in our TDD patient (Figure 1). Hence, we tested its effect in TANGO2^−/− hiPSC-CMs. Acute administration of 400 nmol/L verapamil normalized the prolonged APD₉₀ (Figure 5E) and alleviated AP alternans (Figure 5F) in TANGO2^−/− hiPSC-CMs exposed to 0.1 mmol/L palmitate post-fasting (representative traces in Figure 5D and Supplementary material online, Figure S9D). Given verapamil's known off-target effects on other ion channels such as hERG,^31,32 we also tested diltiazem, a structurally distinct LTCC blocker. Acute administration of 500 nmol/L diltiazem similarly prevented post-fasting palmitate-induced APD₉₀ prolongation (see Supplementary material online, Figure S11C) and AP alternans (see Supplementary material online, Figure S11D; representative traces in Figure S11A and B). These findings indicate that LTCC blockade ameliorates palmitate-induced arrhythmic phenotypes in TANGO2^−/− hiPSC-CMs. AP parameters are summarized in Supplementary material online, Table S4.

3.6. Measurements of L-type Ca current and intracellular Ca transient

Since verapamil completely prevented the post-fasting palmitate-induced AP prolongation and AP alternans in TANGO2^−/− hiPSC-CMs (Figure 5E and F), we initially reasoned that this effect resulted from normalization of increased LTCC activity. However, voltage-clamp experiments revealed no differences in L-type Ca current (I_Ca) (see Supplementary material online, Figure S12B), steady-state inactivation (see Supplementary material online, Figure S12C), or time constant (tau) of I_Ca inactivation (see Supplementary material online, Figure S12D) between control and TANGO2^−/− hiPSC-CMs under either glucose (5.6 mmol/L) or post-fasting palmitate (0.1 mmol/L) conditions. Notably, while tau became slower in both cell types under post-fasting palmitate conditions compared to glucose, this change was similar between groups. These findings suggest that the palmitate-induced APD prolongation in TANGO2^−/− hiPSC-CMs results from altered intracellular Ca handling rather than LTCC dysfunction.

To test this hypothesis, we quantified intracellular Ca handling in fura-2-loaded hiPSC-CMs (Figure 6A) exposed to 0.1 mmol/L palmitate post-fasting. At 0.5 Hz pacing, TANGO2^−/− hiPSC-CMs exhibited several Ca handling abnormalities: elevated diastolic Ca (Figure 6B), slower Ca transient decay kinetics (ԏ) (Figure 6C) with reduced K_SERCA (SERCA-dependent Ca clearance rate constant, 1/s; Supplementary material online, Table S2), reduced fractional sarcoplasmic reticulum (SR) Ca release (Figure 6D), and increased Ca transient alternans ratio (Figure 6E). However, Ca transient amplitude, SR Ca content, and NCX function were comparable between control and TANGO2^−/− hiPSC-CMs (see Supplementary material online, Table S2).

3.7. The effects of verapamil on Ca transient, palmitate oxidation, and cellular energy status

Verapamil decreases Ca influx through LTCC, and thereby can prevent cytosolic Ca overload and restore intracellular Ca balance in experimental models of heart failure or mitochondrial dysfunction.^33,34 Pre-treatment with 100 nmol/L verapamil for 1 h normalized palmitate-induced diastolic Ca elevation in TANGO2^−/− hiPSC-CMs post-fasting (Figure 6B). Following verapamil treatment, TANGO2^−/− hiPSC-CMs showed significantly elevated Ca transient peak amplitude (see Supplementary material online, Table S2) and fractional SR Ca release compared to control (Figure 6D), with markedly faster decay kinetics (Figure 6C) and higher SERCA-dependent Ca clearance rate constant (see Supplementary material online, Table S2). Importantly, verapamil normalized the elevated Ca transient alternans ratio in TANGO2^−/− hiPSC-CMs (Figure 6E). These results emphasize that verapamil can reverse intracellular Ca mishandling in TANGO2^−/− hiPSC-CMs.

Beyond normalizing Ca handling, verapamil reduces myocardial oxygen demands and preserves energy metabolism in ischaemic heart disease.³⁵ We therefore tested its bioenergetic effects in hiPSC-CMs. Pretreatment with 100 nmol/L verapamil for 1 h significantly reduced palmitate-dependent OCR in both control and TANGO2^−/− hiPSC-CMs (see Supplementary material online, Figure S13A and B). Despite lowering overall ATP production rate (see Supplementary material online, Figure S13C), verapamil normalized ATP/ADP ratios in TANGO2^−/− hiPSC-CMs (see Supplementary material online, Figure S13D), eliminating differences between control and TANGO2^−/− hiPSC-CMs. We interpret this result as verapamil reducing oxygen consumption and energetic demand without reversing the underlying palmitate oxidation defect in TANGO2^−/− hiPSC-CMs. This suggests that verapamil's therapeutic benefit in TDD is linked to its ability to reduce Ca accumulation and lower ATP utilization, thereby correcting the cellular energetic deficit.

To test whether reducing ATP consumption alone could be therapeutic, we evaluated mavacamten (MYK-461), a myosin ATPase inhibitor. Given that actomyosin-ATPase accounts for ∼70% of myocardial energy expenditure,³⁶ MYK-461 provides an alternative approach to reduce cellular energy demand. Pretreatment with 1 µmol/L MYK-461 significantly increased ATP/ADP ratios in TANGO2^−/− hiPSC-CMs while not affecting control cells, normalizing the difference between groups (see Supplementary material online, Figure S13E). Together, these results demonstrate that reducing ATP consumption either with verapamil or MYK-461 can prevent palmitate-induced ATP deficiency in TANGO2^−/− hiPSC-CMs.

3.8. The effects of TRPM4 on APs and energy status in TDD

While our results provide mechanistic insights into cellular ATP deficiency (Figure 2) and the therapeutic effect of verapamil and vitamin B supplements in TDD (Figure 5; Supplementary material online, Figure S7), the molecular link between energetic deficit and AP prolongation remains unclear. We focused on TRPM4, a Ca-activated non-selective cation channel that is activated by both ATP depletion and elevated intracellular Ca.^8,37,38 Since palmitate induces both ATP deficiency and Ca dysregulation in TANGO2^−/− hiPSC-CMs post-fasting, we investigated whether these conditions alter TRPM4 expression. RT-qPCR analysis revealed a 39% increase in TRPM4 mRNA expression in TANGO2^−/− hiPSC-CMs exposed to 0.1 mmol/L palmitate after 24-h fasting (Figure 7A).

To determine whether increased TRPM4 expression contributes to APD prolongation, we tested 9-phenanthrol, a TRPM4 inhibitor. Representative AP traces are shown in Supplementary material online, Figure S13A. Acute administration of 10 µmol/L 9-phenanthrol eliminated palmitate-induced APD₉₀ prolongation in TANGO2^−/− hiPSC-CMs post-fasting, normalizing APD₉₀ to control levels (see Supplementary material online, Figure S14B) without changing other AP parameters (e.g. resting potential, AP upstroke, Supplementary material online, Table S5). However, 9-phenanthrol also shortened APD in control hiPSC-CMs (see Supplementary material online, Figure S14A), consistent with its known off-target effects on Ca and K channels.

To specifically assess the role of TRPM4, we performed siRNA-mediated TRPM4 knockdown (Figure 7B). TRPM4 knockdown completely restored APD₉₀ in TANGO2^−/− hiPSC-CMs while having no effect on control cells (Figure 7C and D), confirming TRPM4 as the key mediator of AP prolongation in TANGO2^−/− hiPSC-CMs. siRNA-mediated TRPM4 knockdown only shortened AP repolarization parameters (e.g. APD₉₀), whereas other AP parameters were not altered (see Supplementary material online, Table S6). Furthermore, when 9-phenanthrol was applied to TRPM4 siRNA-treated hiPSC-CMs, it produced no significant additional effect on AP repolarization (see Supplementary material online, Figure S14B and C) or other AP parameters (see Supplementary material online, Table S5) in either control or TANGO2^−/− hiPSC-CMs, providing independent evidence for the mechanistic role of TRPM4 regulating AP repolarization in TANGO2^−/− hiPSC-CMs. We next measured cellular energetics in siRNA-treated TANGO2^−/− hiPSC-CMs. TRPM4 knockdown did not affect palmitate-dependent OCR (see Supplementary material online, Figure S15A and B), ATP production rate (see Supplementary material online, Figure S15C), or ATP/ADP ratios (see Supplementary material online, Figure S15D), demonstrating that TRPM4 acts downstream of the metabolic defect rather than correcting it.

These results establish TRPM4 activation as the critical mechanism linking cellular ATP deficiency to APD prolongation in TDD, positioning it as a potential therapeutic target for preventing metabolic crisis-induced arrhythmia.

4. Discussion

In this study, we demonstrated that TANGO2 deficiency compromises palmitate oxidation in hiPSC-CMs, leading to substrate-specific ATP deficiency that intensifies during fasting. This ATP deficiency activates TRPM4, which serves as a critical ‘metabolic sensor’ that translates ATP deficiency into AP prolongation and cardiac arrhythmias. Importantly, we identified effective therapeutic interventions at multiple levels: acute electrical stabilization with verapamil, metabolic correction with vitamin B5/B9 supplementation, and direct TRPM4 inhibition. These findings establish the mechanistic pathway from metabolic dysfunction to electrical instability in TDD and provide rational therapeutic targets.

4.1. TDD-induced fatty acid oxidation disorder and metabolic crisis

While clear genotype-phenotype correlations have not been established in TDD, clinical observations suggest that different mutations may produce varying degrees of severity.^5,19 Most pathogenic missense variants associate with severe clinical outcomes, though this may reflect ascertainment bias towards more severely affected patients requiring medical attention. The Exons 3–9 deletion investigated in this study represents the most common pathogenic variant, occurring in 60–70% of reported cases and present homozygous in our index patient, providing strong rationale for modelling this specific mutation.

While hiPSC-CMs are more immature than adult cardiomyocytes, an important consideration in hiPSC-CM disease modelling is whether observed phenotypes reflect developmental immaturity or disease pathophysiology. Our data support the latter. Both TANGO2^−/− and control hiPSC-CMs achieve comparable maturation: they exhibit adult-like substrate preference for fatty acid (Figure 2F and G), express similar levels of maturation markers including ion channels, Ca handling proteins, contractile genes, and mitochondrial genes (see Supplementary material online, Figure S6), and demonstrate comparable electrophysiological function under glucose conditions, including preserved QRS duration and field potential characteristics (Figure 3). The critical distinction is that TANGO2^−/− hiPSC-CMs exhibit impaired metabolic capacity specifically under stress—they possess mature metabolic machinery but cannot efficiently sustain fatty acid oxidation during energetic challenge (Figure 2C–E). This represents a conditional metabolic vulnerability rather than a global maturation defect, appropriately recapitulating the clinical phenotype of TDD where patients develop arrhythmia specifically during metabolic stress such as fasting or illness, not under baseline conditions.¹⁸

Our study reveals that TANGO2 deficiency causes selective palmitate oxidation impairment while preserving glucose oxidation, representing a conditional rather than constitutive mitochondrial defect. Although a previous report of reduced OXPHOS complex proteins in TANGO2-deficient human breast cells,³⁹ our TANGO2^−/− hiPSC-CMs maintained normal levels of OXPHOS complex proteins (see Supplementary material online, Figure S4) and preserved baseline mitochondrial function under glucose conditions, with intact OXPHOS and ATP production rates (see Supplementary material online, Figure S3). Mitochondrial dysfunction emerges only when cells relied on palmitate as the sole energy substrate (Figure 2), showing a substrate-specific vulnerability that mirrors clinical TDD metabolic crisis triggers. This cell-type-specific preservation of basal mitochondrial function in cardiomyocytes suggests that TANGO2's role in mitochondrial regulation varies across tissues, with the heart maintaining compensatory mechanisms that become overwhelmed only during metabolic crisis.

The heart normally derives 40–60% of ATP from fatty acid oxidation, increasing to 70% during fasting.^40,41 Our control hiPSC-CMs demonstrated this metabolic flexibility, showing 68% mitochondrial ATP from palmitate, increasing to 77% post-fasting (see Supplementary material online, Figure S2). However, TANGO2^−/− hiPSC-CMs exhibit selective palmitate-dependent ATP deficiency without compensatory glycolysis upregulation (see Supplementary material online, Figure S2), causing an energy crisis that intensified post-fasting (Figure 2C and D; Supplementary material online, Figure S2) and precipitated acute cardiac manifestations (Figures 3E and 4C and D). This substrate-specific defect bridges molecular pathology with episodic clinical presentations, supporting therapeutic strategies that target metabolic support during vulnerable periods.

4.2. Linking metabolic alterations to intracellular Ca dysregulation and cardiac arrhythmias

In cardiomyocytes, approximately 10% of ATP maintains membrane ion channels and transporters crucial for cardiac electrophysiology.⁴² ATP deficiency can compromise these ATP-dependent systems, potentially initiating cardiac arrhythmia.^43,44 This connection is evident in TDD, where impaired palmitate oxidation causes cardiomyocyte ATP deficiency that worsens during fasting (Figure 2A, C, and D).

Our findings establish a direct link between ATP deficiency and APD prolongation in TANGO2^−/− hiPSC-CMs. With glucose as the sole substrate, energy balance remains stable (Figure 2A; Supplementary material online, Figure S3) and APD remains normal in TANGO2^−/− hiPSC-CMs (Figure 4). However, palmitate disrupts myocardial ATP generation in TANGO2^−/− hiPSC-CMs (Figure 2D), leading to APD prolongation and AP alternans that worsen dramatically post-fasting (Figure 4). Critically, restoring ATP levels through creatine kinase/PCr or Mg-ATP prevents these electrical abnormalities (Figure 5B and C; Supplementary material online, Figure S10), demonstrating that ATP deficiency is both necessary and sufficient for arrhythmogenesis in TDD.

The progression from metabolic crisis to electrical instability was comprehensively captured by field potential measurements at 37°C. TANGO2^−/− hiPSC-CMs exhibited substrate-dependent escalation of arrhythmogenic markers: under glucose conditions, electrical function remained normal; palmitate exposure triggered FPD prolongation and FPD alternans; and post-fasting palmitate conditions induced the arrhythmogenic phenotype with increased TampA and TampA alternans (Figure 3). This metabolic stress-dependent progression directly recapitulates the clinical transition to T-wave alternans observed in our TDD patient before torsades de pointes (Figure 1), validating the physiological relevance of our hiPSC-CM model. These converging electrophysiological signatures—prolonged repolarization, beat-to-beat instability, and increased dispersion—represent the established precursors to life-threatening ventricular arrhythmias.

The mechanism involves multiple pathways. ATP deficiency compromises the Na/K ATPase function, reducing outward pump current and causing intracellular Na and Ca accumulation.⁴⁵ Additionally, TRPM4 activation significantly contributes to APD prolongation (discussed below).

Beyond electrical activity, ATP regulates intracellular Ca homeostasis. Approximately 20% of cellular ATP maintains SR Ca-ATPase (SERCA) and ryanodine receptor 2 (RyR2) function.^42,46 Palmitate-induced ATP deficiency in TANGO2^−/− hiPSC-CMs compromises SERCA, reducing SERCA-dependent Ca clearance rate constant (see Supplementary material online, Table S2), prolonging Ca transient decay (Figure 6C) and elevating diastolic Ca (Figure 6B). This activates forward-mode NCX, causing membrane depolarization and APD prolongation. Concurrently, reduced ATP increases free Mg, which inhibits RyR2,⁴⁷ while elevated ADP binds to the closed RyR2 states, further suppressing RyR2 activity.⁴⁸ These combined effects reduce fractional SR Ca release (Figure 6D). Given that both Ca release via RyR2 and Ca uptake via SERCA are inhibited under conditions of energy deficiency, the SR's capacity to store Ca remained unaltered (see Supplementary material online, Table S2).

Ca alternans—the beat-to-beat variation in Ca transient amplitude—depends on I_Ca, SR Ca content, and RyR2 activity.^49,50 Since I_Ca and SR Ca content remain unchanged (see Supplementary material online, Figure S12 and Table S2), suppressed RyR2 activity drives increased Ca alternans in TANGO2^−/− hiPSC-CMs (Figure 6E). Elevated diastolic Ca further inactivates RyR2, amplifying alternans.⁵¹ This Ca alternans, in turn, translates to AP alternans through effects on membrane currents (Figure 4D).

Notably, palmitate slows LTCC inactivation kinetics equally in both cell types (see Supplementary material online, Figure S12D) but only causes APD prolongation in TANGO2^−/− hiPSC-CMs due to their energetic vulnerability and subsequent TRPM4 activation.

4.3. TRPM4—the critical sensor of metabolic crisis

In cardiomyocytes, ATP deficiency affects multiple ATP-dependent processes. However, our focus on TRPM4 in TDD stems from the following evidence. First, the magnitude of electrical dysfunction in TANGO2^−/− hiPSC-CMs far exceeds what classical ATPase-dependent mechanisms alone would predict. For example, while Na/K ATPase inhibition with ouabain causes 21% APD₉₀ prolongation,⁵² TANGO2^−/− hiPSC-CMs exhibit 86% prolongation during palmitate-induced ATP deficiency (Figure 4C), a 1.9-fold greater effect implicating additional mechanisms. Second, TRPM4 uniquely functions as a dual sensor of both ATP deficiency and Ca dysregulation—the two hallmarks of TDD metabolic crisis. Unlike other ion channels, TRPM4 activity is directly modulated by both intracellular ATP levels (with ATP binding inhibiting channel function) and Ca concentrations. Third, TRPM4 expression is significantly upregulated during metabolic crisis in TANGO2^−/− hiPSC-CMs (Figure 7A). Fourth, both siRNA-mediated TRPM4 knockdown and pharmacological TRPM4 inhibition completely normalized prolonged APD in TANGO2^−/− hiPSC-CMs during metabolic crisis (Figure 7D; Supplementary material online, Figure S14B).

TRPM4 contains ATP-binding sites that inhibit channel activity when occupied. Reduced ATP levels relieves this inhibition, activating the channel.^11,53–55 The proposed mechanism for TRPM4-induced APD prolongation involves three steps: (i) ATP deficiency activates TRPM4, increasing Na influx; (ii) elevated intracellular Na promotes reverse-mode NCX, delaying repolarization and prolonging APD; and (iii) concurrent diastolic Ca elevation further activates TRPM4, creating a feed-forward cycle that amplifies both APD prolongation and Ca accumulation. TRPM4 channels are predominantly expressed in the plasma membrane. The decreased cytosolic ATP/ADP ratio we observed (Figure 2A) would directly relieve ATP-mediated inhibition of these channels, while simultaneously elevated diastolic Ca (Figure 6B) would enhance channel activation. This creates a synergistic activation mechanism that amplifies the electrical consequences of mitochondrial dysfunction. Importantly, TRPM4 knockdown does not correct the underlying ATP deficiency—palmitate-dependent OCR, ATP production, and ATP/ADP ratios remain abnormal in TANGO2^−/− hiPSC-CMs (see Supplementary material online, Figure S15). This indicates that TRPM4 is a crucial amplifier of metabolic dysfunction rather than a primary driver of the metabolic defect itself.

TRPM4 expression patterns across cardiac tissue explain the selective vulnerability of ventricular myocardium in TDD. While Purkinje fibres constitutively express high levels of TRPM4, our TANGO2-deficient patient presented with ventricular arrhythmias and QT prolongation without classic conduction system abnormalities (Figure 1). This tissue-specific vulnerability likely reflects the metabolic substrate preference of difference cardiac tissues: Purkinje cardiomyocytes preferentially utilize glucose rather than fatty acids as their energy substrates,^56–58 and would therefore be relatively protected from the metabolic stress triggered by impaired fatty acid oxidation in TDD. Since TANGO2 deficiency specifically impairs palmitate oxidation while preserving glucose metabolism (Figure 2F and G; Supplementary material online, Figure S3), ventricular cardiomyocytes—which rely heavily on fatty acid oxidation—experience severe ATP deficiency during fasting-induced metabolic crisis, while Purkinje cardiomyocytes remain relatively unaffected.

While ventricular cardiomyocytes normally express low baseline TRPM4, our data demonstrate that stress-induced TRPM4 upregulation in TANGO2^−/− hiPSC-CMs under metabolic crisis conditions (Figure 7A). This upregulation, combined with ATP deficiency (which relieves TRPM4 inhibition) and elevated intracellular Ca (which activates TRPM4), creates conditions for robust channel activity despite modest baseline expression. The functional significance of this stress-activated TRPM4 is established by our findings that both pharmacological TRPM4 inhibition and genetic knockdown completely rescues APD prolongation (Figure 7D; Supplementary material online, Figure S14B). This indicates that ventricular cardiomyocyte dysfunction, rather than conduction system abnormalities, drives the arrhythmic phenotype in TDD, explaining why ventricular tissue is selectively vulnerable despite lower baseline TRPM4 expression compared to Purkinje fibres.

4.4. Myocardial protection by verapamil or vitamin B supplementation: therapeutic implication and clinical validation

Our findings validate two complementary therapeutic approaches: (i) acute electrical stabilization with LTCC blocker verapamil (Figure 5D–F) and (ii) long-term metabolic correction with vitamin B supplementation (see Supplementary material online, Figure S7), illustrating the power of using hiPSC-CMs for TDD modelling in vitro.

Verapamil achieves therapeutic effect through LTCC blockade, shortening APD by limiting Ca influx and curtailing plateau phase duration. Despite unchanged I_Ca (see Supplementary material online, Figure S12), verapamil prevents palmitate-induced APD prolongation in TANGO2^−/− hiPSC-CMs post-fasting (Figure 5E). Beyond direct LTCC effects, verapamil reduces mitochondrial oxygen consumption (see Supplementary material online, Figure S13A–D) through a Ca-dependent mechanism: decreased Ca influx reduces Ca signalling to mitochondria, which diminishes activation of Ca-dependent dehydrogenases in the TCA cycle, consequently leading to reduced OXPHOS and lower OCR.^33,59 Simultaneously, verapamil decreases cellular energy demand by reducing ATP consumption.⁶⁰ This dual effect—reduced energy production coupled with greater reduction in energy demand—results in net ATP preservation, beneficial in TANGO2^−/− hiPSC-CMs with pre-existing ATP deficits. The preserved ATP stores enhance SERCA function by increasing SERCA-dependent Ca clearance rate constant (see Supplementary material online, Table S2), accelerates Ca transient decay, and improves RyR2 activity (Figure 6), thereby suppressing alternans and stabilizing electrical activity (Figure 5D–F). In contrast, verapamil treatment reduced SERCA-dependent Ca clearance rate constant in control hiPSC-CMs (see Supplementary material online, Table S2), consistent with its known effect of reducing Ca influx through LTCC and consequently lowering cytosolic Ca driving SERCA reuptake.⁶¹

4.5. Combined vitamins B5 (pantothenic acid) and B9 (folate) supplementation addresses metabolic defects specific to TANGO2 deficiency

Vitamin B supplementation has shown promising results in TDD patients enrolled in a natural history study,²¹ with our patient experiencing two crisis-free years following vitamin B-complex initiation, allowing verapamil discontinuation. Mechanistically, vitamin B5 provides coenzyme A precursors essential for palmitate oxidation,⁶² while B9 enhances cystathionine to cysteine conversion, improving substrate availability for CoA biosynthesis (see Supplementary material online, Figure S8G). Our experimental data demonstrate synergistic effects (see Supplementary material online, Figure S7), with combined B5/B9 treatment significantly increasing palmitate-dependent OCR (see Supplementary material online, Figure S7B) and ATP production rate (see Supplementary material online, Figure S7C) in TANGO2^−/− hiPSC-CMs, effectively normalizing the ATP deficiency that neither vitamin achieved alone, supporting a multi-targeted therapeutic approach that addresses the metabolic dysfunction in TDD beyond simply recapitulating clinical practice.

Our findings expand on Xu et al.'s demonstration that supraphysiological folate concentrations (100 mg/L) suppresses TDD arrhythmia independent of metabolic correction within 12 h,²³ whereas our 2-week physiological B5/B9 supplementation targets the root metabolic defect. Although the clinical efficacy of high-dose folate remains to be tested in TDD patients, the results from Xu et al. and our study suggest a new therapeutic paradigm: high-dose B9 for acute arrhythmia suppression, and physiological B-vitamin supplementation for long-term stabilization.

Our patient's clinical response—immediate arrhythmia suppression with verapamil, followed by two crisis-free years on vitamin B supplementation—is consistent with the multi-level intervention strategy discovered in our human iPSC TDD model and supports the clinical translation of our mechanistic discoveries.

5. Conclusion

Our study establishes TRPM4 as the critical sensor translating metabolic crisis into electrical arrhythmias. These findings support developing metabolic strategies that preserve ATP levels and TRPM4-targeted therapies to prevent cardiac arrhythmias in TDD. More broadly, our work provides a paradigm for understanding the intersection of metabolic dysfunction and cardiac electrical disease, with implications that extend beyond TDD to other conditions where ATP deficiency contributes to arrhythmogenesis.

Supplementary Material

cvag143_Supplementary_Data

cvag143_supplementary_data.zip^{(5.2MB, zip)}

Acknowledgement

The Agilent Seahorse Extracellular Flux Analyzer is housed and managed within the Vanderbilt High-Throughput Screening Core Facility, an institutionally supported core, and was funded by NIH Shared Instrumentation Grant 1S10OD018015.

Contributor Information

Lili Wang, Vanderbilt Center for Arrhythmia Research and Therapeutics, Division of Clinical Pharmacology, Vanderbilt University Medical Center, 2215B Garland Ave, Nashville, TN 37232-0575, USA.

Kyungsoo Kim, Vanderbilt Center for Arrhythmia Research and Therapeutics, Division of Clinical Pharmacology, Vanderbilt University Medical Center, 2215B Garland Ave, Nashville, TN 37232-0575, USA.

Prince J Kannankeril, Thomas P. Graham Jr. Division of Pediatric Cardiology and the Center for Pediatric Precision Medicine, Department of Pediatrics, Monroe Carell Jr. Children’s Hospital at Vanderbilt and Vanderbilt University Medical Center, Nashville, TN, USA.

Chen Zheng, Department of Pharmacology, Vanderbilt University, Nashville, TN, USA.

Daniel J Blackwell, Vanderbilt Center for Arrhythmia Research and Therapeutics, Division of Clinical Pharmacology, Vanderbilt University Medical Center, 2215B Garland Ave, Nashville, TN 37232-0575, USA.

Samuel J Mackenzie, Department of Neurology, University of Rochester Medicine, Rochester, NY, USA.

Paul S Brookes, Department of Anesthesiology, University of Rochester Medicine, Rochester, NY, USA.

Björn C Knollmann, Vanderbilt Center for Arrhythmia Research and Therapeutics, Division of Clinical Pharmacology, Vanderbilt University Medical Center, 2215B Garland Ave, Nashville, TN 37232-0575, USA.

Supplementary material

Supplementary material is available at Cardiovascular Research online.

Authors’ contributions

Study design: L.W., P.J.K., S.J.M., P.S.B., and B.C.K.; methodology, acquisition of data, and analysis of data: L.W., K.K., P.J.K., C.Z., and D.J.B.; writing of the manuscript: L.W., D.J.B., and B.C.K.; and review and edition of the manuscript: L.W., K.K., P.J.K., S.J.M., P.S.B., C.Z., D.J.B., and B.C.K.

Funding

The work was supported by Leducq Foundation 18CVD05 (to B.C.K.), the National Institutes of Health NHLBI R35 HL144980 (to B.C.K.), and TANGO2 Research Foundation (to L.W. and S.J.M.). Work in the lab of P.S.B. is funded by National Institutes of Health R01HL071158. There are no relationships with the industry.

Data availability

The data generated in this study are available in the article and in its online supplementary material.

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Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Supplementary Materials

cvag143_Supplementary_Data

cvag143_supplementary_data.zip^{(5.2MB, zip)}

Data Availability Statement

The data generated in this study are available in the article and in its online supplementary material.

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PERMALINK

Metabolic crisis and TRPM4 activation cause QT prolongation in TANGO2 deficiency disorder

Lili Wang

Kyungsoo Kim

Prince J Kannankeril

Chen Zheng

Daniel J Blackwell

Samuel J Mackenzie

Paul S Brookes

Björn C Knollmann

Abstract

Aims

Methods and results

Conclusion

Graphical Abstract

Graphical Abstract.

1. Introduction

2. Methods

2.1. Statistical analysis

3. Results

3.1. TDD: a clinical case study

Figure 1.

3.2. Development of TANGO2−/− hiPSC model

3.3. Cellular bioenergetic function

Figure 2.

3.4. Synergistic vitamin B5/B9 treatment and palmitate oxidation

3.5. Metabolic substrate-dependent electrical regulation

Figure 3.

Figure 4.

Figure 5.

3.6. Measurements of L-type Ca current and intracellular Ca transient

Figure 6.

3.7. The effects of verapamil on Ca transient, palmitate oxidation, and cellular energy status

3.8. The effects of TRPM4 on APs and energy status in TDD

Figure 7.

4. Discussion

4.1. TDD-induced fatty acid oxidation disorder and metabolic crisis

4.2. Linking metabolic alterations to intracellular Ca dysregulation and cardiac arrhythmias

4.3. TRPM4—the critical sensor of metabolic crisis

4.4. Myocardial protection by verapamil or vitamin B supplementation: therapeutic implication and clinical validation

4.5. Combined vitamins B5 (pantothenic acid) and B9 (folate) supplementation addresses metabolic defects specific to TANGO2 deficiency

5. Conclusion

Supplementary Material

Acknowledgement

Contributor Information

Supplementary material

Authors’ contributions

Funding

Data availability

References

Associated Data

Supplementary Materials

Data Availability Statement

ACTIONS

PERMALINK

RESOURCES

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Links to NCBI Databases

3.2. Development of TANGO2^−/− hiPSC model