Spatial Transcriptomics in the Human Left Atrial Appendage and Pulmonary Vein Sleeve

Human left atrial appendage (LAA) and pulmonary vein (PV) tissues were obtained from unused lung or heart transplant donors. Paired LAA and PV sleeve tissues were obtained from two subjects, and an additional 6 PV samples were obtained from other donors. After tissue sectioning and staining, spatial RNAseq was performed. mRNAs from~1000 to 2500 genes were sequenced in each spatial area. Seurat clustering yielded 15 different clusters. These grossly split into two segregating populations, the left and right sides, with one connecting population. Multiple cells and cell types may reside in each 55 µm diameter spatial area. A clear asymmetry of clusters was observed in the PV sections, with less asymmetry in the LAA sections. Cell-type marker genes derived from human LAA single nuclei RNAseq were used to determine the dominant cell types in the 15 different clusters. The left side segregating clusters were enriched in cardiomyocytes, while the right side segregating clusters were enriched for other 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 was also mapped, confirming higher expression of the cardiac master transcription factor SHOX2 in the PV vs. LAA tissues. Expression of the hyperpolarization-activated ion channel HCN4 was sporadic in both PV and LAA specimens.