Arrhythmogenic cardiomyopathy (ACM) is a myocardial genetic disease whose cardinal manifestations are ventricular arrhythmias, sudden death, myocardial fibro-adiposis, cell death, and heart failure. ACM is caused primarily by mutations in genes encoding desmosome proteins, including desmoplakin (DSP). In the heart, desmosomes are mainly present in myocytes and are responsible for myocardial mechanical integrity. They are also hubs for mechanosensing and transduction, including the Hippo and canonical WNT (cWNT) pathways, which are involved in ACM. Desmosome proteins are also expressed in the epicardium, the site of initial manifestations of ACM phenotype. Specific role(s) of the epicardial cells in the pathogenesis of ACM is unknown. The cWNT pathway has emerged as an attractive therapeutic target in ACM. Experimental data, however, are conflicting, with a spectrum ranging from suppression to activation of the cWNT in ACM. The ambiguity along with potential fortuitous effects of systemic targeting of this major regulatory pathway have raised considerable trepidations, leading to an impasse on therapeutic targeting of the cWNT pathway in ACM. We provide data in human and mouse hearts with ACM suggesting that the ambiguity is in part due to determining the cWNT activity in cellularly heterogeneous myocardium. Accordingly, whereas the cWNT is activated in cardiac myocytes, the whole myocardium is exposed to increased levels of secreted cWNT inhibitors (cWNT-Is). The dysregulation is remarkable in the human hearts with ACM as transcript levels of 26 cWNT-Is are increased, including SFRP3 protein, a classic cWNT-I. To resolve the uncertainty, we will use an uncommitted approach of activating or suppressing the cWNT pathway specifically in cardiac myocytes and epicardial cells and determining the phenotypic effects, including effects on expression of secreted cWNT-Is. Inducible Cre-deleter mice will be used to delete Dsp in cardiac myocytes or epicardial cells post-natally while concomitantly suppressing or activating the cWNT using loss- and gain-of-function b-catenin mice. Cardiac function, arrhythmias, apoptosis, fibro-adipogenesis and gene expression, including secretome in myocytes and epicardial cells will be characterized. Dsp+/- epicardial cells will be conditionally tagged using the dual reporter (Rosa26mT/mG) mice and their differentiation to other cardiac cells will be analyzed by fate mapping. Tagged cells derived from Dsp+/- epicardial cells will be isolated and analyzed by single cell RNA-Seq to determine their transcriptional identity and identify secretome expressed by each subset of epicardial-derived cells. Likewise, effects of activation or suppression of the cWNT pathway on differentiation of the Dsp+/- epicardial cells to other cardiac cell types and the secretome will be determined using gain- and loss-of-function b-catenin mice. The findings will determine whether cell-type specific targeting of the cWNT is a beneficial therapeutic approach in ACM, will define the role of epicardial cells in ACM, and could lead to identification of secreted factors that might serve as diagnostic and prognostic biomarkers and therapeutic targets in ACM.
Arrhythmogenic cardiomyopathy (ACM) is a difficult to diagnose primary disease of myocardium for which there is no effective therapy. We propose to determine effects of cell type-specific therapeutic targeting the canonical WNT pathway in ACM and identify secreted paracrine factors that might contribute to pathogenesis of the disease, serve as therapeutic targets, and are used as diagnostic and prognostic biomarkers.
