Human pancreatic α-cell heterogeneity and trajectory inference analyses reveal SMOC1 as a β-cell dedifferentiation gene

β-cell dysfunction and dedifferentiation towards an α-cell-like phenotype are hallmarks of type 2 diabetes. However, the cell subtypes involved in β-to-α-cell transition are unknown. Using single-cell and single-nucleus RNA-seq, RNA velocity, PAGA/cell trajectory inference, and gene commonality, we interrogated α-β-cell fate switching in human islets. We found five α-cell subclusters with distinct transcriptomes. PAGA analysis showed bifurcating cell trajectories in non-diabetic while unidirectional cell trajectories from β-to-α-cells in type 2 diabetes islets suggesting dedifferentiation towards α-cells. Ten genes comprised the common signature genes in trajectories towards α-cells. Among these, the α-cell gene SMOC1 was expressed in β-cells in type 2 diabetes. Enhanced SMOC1 expression in β-cells decreased insulin expression and secretion and increased β-cell dedifferentiation markers. Collectively, these studies reveal differences in α-β-cell trajectories in non-diabetes and type 2 diabetes human islets, identify signature genes for β-to-α-cell trajectories, and discover SMOC1 as an inducer of β-cell dysfunction and dedifferentiation.