NFĸB signaling drives myocardial injury via CCR2+ macrophages in a preclinical model of arrhythmogenic cardiomyopathy

Nuclear factor kappa-B (NFκB) is activated in arrhythmogenic cardiomyopathy (ACM) patient-derived iPSC-cardiac myocytes under basal conditions and inhibition of NFκB signaling prevents disease in Dsg2mut/mut mice, a robust mouse model of ACM. Here, we used genetic approaches and single cell RNA sequencing to define the contributions of immune signaling in cardiac myocytes and macrophages in the natural progression of ACM using Dsg2mut/mut mice. We found that NFκB signaling in cardiac myocytes drives myocardial injury, contractile dysfunction, and arrhythmias in Dsg2mut/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 Dsg2mut/mut mice is caused both by loss of heart muscle and negative inotropic effects of inflammation in viable muscle. Single nucleus RNA sequencing and cellular indexing of transcriptomes and epitomes (CITE-seq) studies revealed marked pro-inflammatory changes in gene expression and the cellular landscape in hearts of Dsg2mut/mut mice involving cardiac myocytes, fibroblasts and CCR2+ macrophages. Changes in gene expression in cardiac myocytes and fibroblasts in Dsg2mut/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.

Helios Deficiency Predisposes the Differentiation of CD4+Foxp3- T Cells into Peripherally Derived Regulatory T Cells

The transcription factor Helios is expressed in a large percentage of Foxp3⁺ regulatory T (Treg) cells and is required for the maintenance of their suppressive phenotype, as mice with a selective deficiency of Helios in Treg cells spontaneously develop autoimmunity. However, mice with a deficiency of Helios in all T cells do not exhibit autoimmunity, despite the defect in the suppressor function of their Treg cell population, suggesting that Helios also functions in non-Treg cells. Although Helios is expressed in a small subset of CD4⁺Foxp3^- and CD8⁺ T cells and its expression is upregulated upon T cell activation, its function in non-Treg cells remains unknown. To examine the function of Helios in CD4⁺Foxp3^- T cells, we transferred Helios-sufficient or -deficient naive CD4⁺Foxp3^- TCR transgenic T cells to normal recipients and examined their capacity to respond to their cognate Ag. Surprisingly, Helios-deficient CD4⁺ T cells expanded and differentiated into Th1 or Th2 cytokine-producing effectors in a manner similar to wild-type TCR transgenic CD4⁺ T cells. However, the primed Helios-deficient cells failed to expand upon secondary challenge with Ag. The tolerant state of the Helios-deficient memory T cells was not cell-intrinsic but was due to a small population of Helios-deficient naive T cells that had differentiated into Ag-specific peripheral Treg cells that suppressed the recall response in an Ag-specific manner. These findings demonstrate that Helios plays a role in the determination of CD4⁺ T cell fate.

A Treg-specific deletion of Helios causes autoimmune lipodystrophy and metabolic syndrome

Regulatory T (Treg) cells suppress immune activation in a dominant manner and play a critical role in the maintenance of self-tolerance. A subpopulation (60–75%) of Foxp3+T regulatory (Treg) cells express the transcription factor Helios. To examine the function of Helios in Treg cells, we have generated Treg-specific Helios deficient mice (cKO, Heliosflxflx Foxp3cre). Although both Treg development in the cKO mice and their in vitro suppressor function are normal, the selective deletion of Helios in Tregs leads to slow, progressive systemic immune activation with a Th1 phenotype, hypergammaglobulinemia, and enhanced germinal center formation. Initially, we observed significant lymphocytic infiltrates only in the salivary gland and not in any other organs typically affected by Treg dysregulation. Strikingly, the mice developed lipodystrophy, hepatic steotosis and insulin resistance. Further analysis revealed a significant lymphocytic infiltrate in both the inguinal and perigonadal adipose tissue, indicating autoimmune mediated destruction of the white adipose tissue (WAT). We have further shown that the lymphocytic infiltrate specific to WAT can be transferred from mice with lipodystrophy to immunodeficient mice, confirming the autoimmune nature of the lipodystrophy. Thus, Helios deficiency in Treg disrupts immune homeostasis in the adipose tissue, leading to the destruction of WAT and redirection of lipids to the liver, and ultimately causes metabolic dysfunction.

Supported by the Intramural Research Program of the NIAID, NIH.