Spatial transcriptomics in the human left atrial appendage and pulmonary vein sleeve

Isolation of the pulmonary veins (PV) is a primary goal of ablation procedures to treat atrial fibrillation (AF), and the top genetic risk locus for AF is near PITX2, implicated in formation of the PVs. However, the challenges in obtaining PV tissues have limited progress in transcriptomic and mechanistic insights. Human PV and left atrial appendage (LAA) tissues, obtained from unused transplant donors, were used for spatial transcriptomic studies. Multiple cells and cell types may reside in each 55 µm diameter spatial area. Seurat clustering yielded 15 different clusters. Cell-type specific marker genes were used to determine the dominant cell types in these clusters, identifying several clusters enriched for cardiomyocytes, while others were enriched for additional cell types including fibroblasts, vascular smooth muscle cells, endothelial cells, and adipocytes. Spatial transcriptomics clearly resolved the venous, cardiomyocyte, and epicardial regions of the PV tissues, as well as fibrotic regions in LAAs and PVs. Spatial expression of the AF-associated genes PITX2, SHOX2, and HCN4 confirmed presence in LAA and PVs with apparently higher expression of the cardiac master transcription factor SHOX2 in the PV vs. LAA tissues, implicating the potential importance of SHOX2 regulation in the PVs.