The brief opening mode of the mitochondrial permeability transition pore (mPTP) serves as a calcium (Ca²⁺) release valve to prevent mitochondrial Ca²⁺ (mCa²⁺) overload. Catecholaminergic polymorphic ventricular tachycardia (CPVT) is a stress-induced arrhythmic syndrome due to mutations in the Ca²⁺ release channel complex of ryanodine receptor 2 (RyR2). We hypothesize that inhibiting the mPTP opening in CPVT exacerbates the disease phenotype. By crossbreeding a CPVT model of CASQ2 knockout (KO) with a mouse missing CypD, an activator of mPTP, a double KO model (DKO) was generated. Echocardiography, cardiac histology, and live-cell imaging were employed to assess the severity of cardiac pathology. Western blot and RNAseq were performed to evaluate the contribution of various signaling pathways. Although exacerbated arrhythmias were reported, the DKO model did not exhibit pathological remodeling. Myocyte Ca²⁺ handling was similar to that of the CASQ2 KO mouse at a low pacing frequency. However, increased ROS production, activation of the CaMKII pathway, and hyperphosphorylation of RyR2 were detected in DKO. Transcriptome analysis identified altered gene expression profiles associated with electrical instability in DKO. Our study provides evidence that genetic inhibition of mPTP exacerbates RyR2 dysfunction in CPVT by increasing activation of the CaMKII pathway and subsequent hyperphosphorylation of RyR2.

Catecholaminergic polymorphic ventricular tachycardia (CPVT) is a genetic arrhythmic syndrome caused by mutations in the sarcoplasmic reticulum (SR) calcium (Ca ²⁺ ) release channel RyR2 or its accessory proteins, including calsequestrin‐2 (CASQ2). RyR2 dysfunction or leak is the hallmark feature of CPVT and directly triggers arrhythmias. Despite this electrical instability, CPVT hearts are typically anatomically normal and lack pathological remodelling. Therefore, we hypothesized that introducing additional stressors, such as metabolic stress, would worsen cardiac arrhythmias and potentially trigger pathological remodelling. To test this hypothesis, metabolic stress was introduced by crossbreeding a CPVT model of CASQ2 ^−/− mice with the Akita mouse, a genetic model of diabetes that also lacks cardiac remodelling. We found that dysregulation of myocyte Ca ²⁺ handling was exacerbated in Akita‐CASQ2 ^−/− cells, which exhibited slower Ca ²⁺ transient decay kinetics and increased arrhythmogenic Ca ²⁺ waves. Akita‐CASQ2 ^−/− mice also displayed more severe arrhythmias, diastolic dysfunction, and cardiac hypertrophy, but without evidence of fibrosis, cell death, or worsened metabolic dysfunction. Finally, mitochondrial reactive oxygen species production was increased in Akita‐CASQ2 ^−/− cardiomyocytes, which may contribute to the more severe pathological phenotype. Overall, our results suggest that metabolic stress can aggravate dysregulated myocyte Ca ²⁺ handling and promote cardiac dysfunction in CPVT hearts.

Background/Objectives: Aryl hydrocarbon receptor (AHR) ligands are known to suppress antibody production. However, it remains unclear whether this suppression translates into altered antibody-mediated Fcγ receptor signaling in human cells. This study aimed to investigate the effects and mechanisms by which AHR ligands regulate antibody production and antibody-triggered responses in human peripheral blood mononuclear cells (PBMCs). Methods: PBMCs were isolated from blood obtained from anonymous healthy donors. PBMCs were stimulated with pokeweed mitogen (PWM) to induce IgG1 production or Strept-Biotin IgG1/IgG2 immune complexes to induce antibody-triggered signaling. Before any stimulation, cells were pretreated with vehicle (0.01% DMSO) or AHR ligands TCDD (2,3,7,8-tetrachlorodibenzo-p-dioxin), ITE (2-(1H-indol-3-ylcarbonyl)-4-thiazolecarboxylic acid methyl ester), or FICZ (6-formylindolo[3,2-b]carbazole), or the proligand I3C (indole-3-carbinol). Results: Our data revealed that PWM stimulation significantly increased IL6 and IL1B gene expression and PWM-induced IL-6 cytokine secretion, which was significantly suppressed by TCDD, ITE, FICZ, and I3C. However, only TCDD was able to suppress PWM-stimulated IgG1 antibody production. Transcriptomic analysis using I3C revealed upregulated AHR-responsive genes such as CYP1A1, CYP1B1, AHRR and TIPARP in PWM-stimulated human PBMCs. Notably, I3C downregulated genes TRAPPC9 and C1QTNF3, which play a role in NF-κB-associated inflammatory signaling. It also revealed potential sex differences in I3C-mediated gene modulation associated with B cell function, Ig expression, FcγR signaling, and inflammatory pathways. Lastly, IgG1 and IgG2 immune complex-stimulated IL-6 cytokine secretion was significantly suppressed by TCDD, whereas I3C showed modest, although not statistically significant, suppression. Conclusions: Overall, these findings demonstrate that AHR activation by TCDD suppressed antibody production and IgG-mediated immune signaling in human PBMCs.