Fibro-fatty remodelling in arrhythmogenic cardiomyopathy.

Arrhythmogenic cardiomyopathy (AC) is an inherited disorder characterized by lethal arrhythmias and a risk to sudden cardiac death. A hallmark feature of AC is the progressive replacement of the ventricular myocardium with fibro-fatty tissue, which can act as an arrhythmogenic substrate further exacerbating cardiac dysfunction. Therefore, identifying the processes underlying this pathological remodelling would help understand AC pathogenesis and support the development of novel therapies. In this review, we summarize our knowledge on the different models designed to identify the cellular origin and molecular pathways underlying cardiac fibroblast and adipocyte cell differentiation in AC patients. We further outline future perspectives and how targeting the fibro-fatty remodelling process can contribute to novel AC therapeutics.

Epicardial differentiation drives fibro-fatty remodeling in arrhythmogenic cardiomyopathy.

Arrhythmogenic cardiomyopathy (ACM) is an inherited disorder often caused by pathogenic variants in desmosomal genes and characterized by progressive fibrotic and fat tissue accumulation in the heart. The cellular origin and responsible molecular mechanisms of fibro-fatty deposits have been a matter of debate, due to limitations in animal models recapitulating this phenotype. Here, we used human-induced pluripotent stem cell (hiPSC)­derived cardiac cultures, single-cell RNA sequencing (scRNA-seq), and explanted human ACM hearts to study the epicardial contribution to fibro-fatty remodeling in ACM. hiPSC-epicardial cells generated from patients with ACM showed spontaneous fibro-fatty cellular differentiation that was absent in isogenic controls. This was further corroborated upon siRNA-mediated targeting of desmosomal genes in hiPSC-epicardial cells generated from healthy donors. scRNA-seq analysis identified the transcription factor TFAP2A (activating enhancer-binding protein 2 alpha) as a key trigger promoting this process. Gain- and loss-of-function studies on hiPSC-epicardial cells and primary adult epicardial-derived cells demonstrated that TFAP2A mediated epicardial differentiation through enhancing epithelial-to-mesenchymal transition (EMT). Furthermore, examination of explanted hearts from patients with ACM revealed epicardial activation and expression of TFAP2A in the subepicardial mesenchyme. These data suggest that TFAP2A-mediated epicardial EMT underlies fibro-fatty remodeling in ACM, a process amenable to therapeutic intervention.

Cardiomyocytes stimulate angiogenesis after ischemic injury in a ZEB2-dependent manner.

The disruption in blood supply due to myocardial infarction is a critical determinant for infarct size and subsequent deterioration in function. The identification of factors that enhance cardiac repair by the restoration of the vascular network is, therefore, of great significance. Here, we show that the transcription factor Zinc finger E-box-binding homeobox 2 (ZEB2) is increased in stressed cardiomyocytes and induces a cardioprotective cross-talk between cardiomyocytes and endothelial cells to enhance angiogenesis after ischemia. Single-cell sequencing indicates ZEB2 to be enriched in injured cardiomyocytes. Cardiomyocyte-specific deletion of ZEB2 results in impaired cardiac contractility and infarct healing post-myocardial infarction (post-MI), while cardiomyocyte-specific ZEB2 overexpression improves cardiomyocyte survival and cardiac function. We identified Thymosin ß4 (TMSB4) and Prothymosin α (PTMA) as main paracrine factors released from cardiomyocytes to stimulate angiogenesis by enhancing endothelial cell migration, and whose regulation is validated in our in vivo models. Therapeutic delivery of ZEB2 to cardiomyocytes in the infarcted heart induces the expression of TMSB4 and PTMA, which enhances angiogenesis and prevents cardiac dysfunction. These findings reveal ZEB2 as a beneficial factor during ischemic injury, which may hold promise for the identification of new therapies.

The Aryl Hydrocarbon Receptor Antagonist StemRegenin1 Improves In Vitro Generation of Highly Functional Natural Killer Cells from CD34(+) Hematopoietic Stem and Progenitor Cells.

Early natural killer (NK)-cell repopulation after allogeneic stem cell transplantation (allo-SCT) has been associated with reduced relapse rates without an increased risk of graft-versus-host disease, indicating that donor NK cells have specific antileukemic activity. Therefore, adoptive transfer of donor NK cells is an attractive strategy to reduce relapse rates after allo-SCT. Since NK cells of donor origin will not be rejected, multiple NK-cell infusions could be administered in this setting. However, isolation of high numbers of functional NK cells from transplant donors is challenging. Hence, we developed a cytokine-based ex vivo culture protocol to generate high numbers of functional NK cells from granulocyte colony-stimulating factor (G-CSF)-mobilized CD34(+) hematopoietic stem and progenitor cells (HSPCs). In this study, we demonstrate that addition of aryl hydrocarbon receptor antagonist StemRegenin1 (SR1) to our culture protocol potently enhances expansion of CD34(+) HSPCs and induces expression of NK-cell-associated transcription factors promoting NK-cell differentiation. As a result, high numbers of NK cells with an active phenotype can be generated using this culture protocol. These SR1-generated NK cells exert efficient cytolytic activity and interferon-γ production toward acute myeloid leukemia and multiple myeloma cells. Importantly, we observed that NK-cell proliferation and function are not inhibited by cyclosporin A, an immunosuppressive drug often used after allo-SCT. These findings demonstrate that SR1 can be exploited to generate high numbers of functional NK cells from G-CSF-mobilized CD34(+) HSPCs, providing great promise for effective NK-cell-based immunotherapy after allo-SCT.