350-OR: Transcriptomics Identification of a-Cell Subpopulations in Human Islets Using Integrated scRNA-seq and snRNA-seq

Loss of β cells leads to diabetes. α cells are refractory to spontaneous conversion to β cells, but a small percentage are reprogrammed to β cells with acute β cell loss. β cell heterogeneity and identification of β cell subpopulations and their transcriptomic profiles have been reported. However, α cell subpopulations in the human islet have not been clearly defined yet. Moreover, whether specific human α cell subpopulations can potentially evolve into β cells is unknown. Here, we integrated scRNA- and snRNA-seq data of human islets from 3 adult healthy donors to determine α cell subpopulations and their transcriptomic profiles. We extracted the α cell cluster (7,535 cells) and using Louvain resolution 0.8, we identified 5 subclusters: 1) α cells (GCG^high/TTR^high/PTPRT^high); 2) αβ-Transition-1 (αβ-Tr1) cells; 3) αβ-Tr2 cells; 4) αβ1 cells (GCG^high/INS^low/IAPP^low); and 5) αβ2 cells (GCG^low/INS^high/IAPP^high). To investigate the transcriptomics connectivity among clusters, we performed RNA velocity and Partition-based Graph Abstraction (PAGA) analyses. PAGA showed that αβ-Tr1 cells (15.3% of cells) are the root subcluster from where α cells and αβ-Tr2 cells are formed, suggesting a precursor nature. αβ-Tr2 cells are the origin of αβ1 and αβ2 cells. We next projected this finding into the pseudotime algorithm and analyzed gene expression gradients in the trajectories. Interestingly, the αβ-Tr1/αβ-Tr2/αβ2 cells trajectory showed a gradual increase in the expression of β cell genes (INS, ZNF385D, CASR, MAFA) while decreasing expression of ribosomal genes, GCG and MALAT1. Single cell pathway analysis with escape package showed that αβ-Tr1 cells are enriched in ribosome and translation gene pathways and that αβ-Tr2 cells are enriched in transdifferentiation genes INSM1, PDX1 and SMAD3. In summary, these studies identified 5 α cell subpopulations with different transcriptomic profiles and highlight the potential plasticity of αβ-Tr cells to generate αβ cells.