PROJECT SUMMARY LMNA-related dilated cardiomyopathy (DCM) is among the most prevalent forms of inherited heart disease, characterized by severe systolic dysfunction and ventricular chamber enlargement. Major hallmarks of LMNADCM also involve features of non-myocyte dysfunction including myocardial fibrosis and endotheliopathy. However, precise mechanisms of intercellular communication in the heart remain unclear, in part because the human cardiac secretome to date has been poorly defined. To overcome this challenge, we propose to leverage human iPSCs, genome-editing technology, and state-of-the-art omics methods to identify and investigate crosstalk signaling pathways potentially involved in LMNA-DCM pathogenesis. In Aim 1, we will comprehensively profile the baseline secretomes of each cell type by employing high-throughput aptamer-based proteomics methods, and perform trans-well co-culture assays to systematically evaluate the downstream functional consequences of cellular crosstalk. In Aim 2, we will complement these studies with further investigation into intercellular communication mechanisms in engineered heart tissues (EHTs) of varying LMNA-DCM / control cell type compositions. The EHTs will be subsequently analyzed by single-cell RNA sequencing (scRNA-seq) to predict cell-cell crosstalk modalities and construct a list of unique and shared ligand receptor pairs across conditions. In Aim 3, we will perform large-scale high-throughput screening of >4,000 compounds using multicellular iPSC-derived cardiac organoid (iPSC-CO) differentiated from tri-lineage reporter lines. Selected candidates will be validated and further investigated using proteomics and targeted gain/loss-of function studies. We anticipate that the successful completion of these studies will lead to new mechanistic insight into DCM pathogenesis, and help develop novel therapeutic strategies that can impede and reverse aberrant crosstalk signaling between cardiac cell types in the diseased heart.