Nuclear factor κ-B (NFκB) is activated in iPSC-cardiac myocytes from patients with arrhythmogenic cardiomyopathy (ACM) under basal conditions, and inhibition of NFκB signaling prevents disease in Dsg2 ^mut/mut mice, a robust mouse model of ACM. Here, we used genetic approaches and single-cell RNA-Seq to define the contributions of immune signaling in cardiac myocytes and macrophages in the natural progression of ACM using Dsg2 ^mut/mut mice. We found that NFκB signaling in cardiac myocytes drives myocardial injury, contractile dysfunction, and arrhythmias in Dsg2 ^mut/mut mice. NFκB signaling in cardiac myocytes mobilizes macrophages expressing C-C motif chemokine receptor-2 (CCR2 ⁺ cells) to affected areas within the heart, where they mediate myocardial injury and arrhythmias. Contractile dysfunction in Dsg2 ^mut/mut mice is caused both by loss of heart muscle and negative inotropic effects of inflammation in viable muscle. Single nucleus RNA-Seq and cellular indexing of transcriptomes and epitomes (CITE-Seq) studies revealed marked proinflammatory changes in gene expression and the cellular landscape in hearts of Dsg2 ^mut/mut mice involving cardiac myocytes, fibroblasts, and CCR2 ⁺ macrophages. Changes in gene expression in cardiac myocytes and fibroblasts in Dsg2 ^mut/mut mice were dependent on CCR2 ⁺ macrophage recruitment to the heart. These results highlight complex mechanisms of immune injury and regulatory crosstalk between cardiac myocytes, inflammatory cells, and fibroblasts in the pathogenesis of ACM.

Arrhythmogenic Cardiomyopathy (ACM) is a familial heart disease, characterized by contractile dysfunction, ventricular arrhythmias (VAs), and the risk of sudden cardiac death. Currently, implantable cardioverter defibrillators and antiarrhythmics are the mainstays in ACM therapeutics. Angiotensin receptor blockers (ARBs) have been highlighted in the treatment of heart diseases, including ACM. Yet, recent research has additionally implicated ARBs in the genesis of VAs and myocardial lipolysis via the peroxisome proliferator-activated receptor gamma (PPARγ) pathway. The latter is of particular interest, as fibrofatty infiltration is a pathological hallmark in ACM. Here, we tested two ARBs, Valsartan and Telmisartan, and the PPAR agonist, Rosiglitazone, in an animal model of ACM, homozygous Desmoglein-2 mutant mice (Dsg2^mut/mut). Cardiac function, premature ventricular contractions (PVCs), fibrofatty scars, PPARα/γ protein levels, and PPAR-mediated mRNA transcripts were assessed. Of note, not a single mouse treated with Rosiglitazone made it to the study endpoint (i.e., 100% mortality: n = 5/5). Telmisartan-treated Dsg2^mut/mut mice displayed the preservation of contractile function (percent ejection fraction [%EF]; 74.8 ± 6.8%EF) compared to Vehicle- (42.5 ± 5.6%EF) and Valsartan-treated (63.1 ± 4.4%EF) mice. However, Telmisartan-treated Dsg2^mut/mut mice showed increased cardiac wall motion abnormalities, augmented %PVCs, electrocardiographic repolarization/depolarization abnormalities, larger fibrotic lesions, and increased expression of PPARy-regulated gene transcripts compared to their Dsg2^mut/mut counterparts. Alternatively, Valsartan-treated Dsg2^mut/mut mice harbored fewer myocardial scars, reduced %PVC, and increased Wnt-mediated transcripts. Considering our findings, caution should be taken by physicians when prescribing medications that may increase PPARy signaling in patients with ACM.

Arrhythmogenic cardiomyopathy (ACM) is a familial heart disease characterized by cardiac dysfunction, arrhythmias, and myocardial inflammation. Exercise and stress can influence the disease’s progression. Thus, an investigation of whether a high-fat diet (HFD) contributes to ACM pathogenesis is warranted. In a robust ACM mouse model, 8-week-old Desmoglein-2 mutant (Dsg2^mut/mut) mice were fed either an HFD or rodent chow for 8 weeks. Chow-fed wildtype (WT) mice served as controls. Echo- and electrocardiography images pre- and post-dietary intervention were obtained, and the lipid burden, inflammatory markers, and myocardial fibrosis were assessed at the study endpoint. HFD-fed Dsg2^mut/mut mice showed numerous P-wave perturbations, reduced R-amplitude, left ventricle (LV) remodeling, and reduced ejection fraction (%LVEF). Notable elevations in plasma high-density lipoprotein (HDL) were observed, which correlated with the %LVEF. The myocardial inflammatory adipokines, adiponectin (AdipoQ) and fibroblast growth factor-1, were substantially elevated in HFD-fed Dsg2^mut/mut mice, albeit no compounding effect was observed in cardiac fibrosis. The HFD not only potentiated cardiac dysfunction but additionally promoted adverse cardiac remodeling. Further investigation is warranted, particularly given elevated AdipoQ levels and the positive correlation of HDL with the %LVEF, which may suggest a protective effect. Altogether, the HFD worsened some, but not all, disease phenotypes in Dsg2^mut/mut mice. Notwithstanding, diet may be a modifiable environmental factor in ACM disease progression.