Deep single-cell decoding of human pancreatic islets reveals T2D β-cell gene expression defects

Pancreatic islets maintain glucose homeostasis through coordinated action of endocrine and affiliate cell types and are central to type 2 diabetes (T2D) genetics and pathophysiology. Our understanding of robust human islet cell type-specific alterations in T2D remains limited. Here, we report comprehensive single-cell transcriptome profiling of 245,878 human islet cells from 48 donors spanning non-diabetic, pre-diabetic, and T2D states, and we identify 14 distinct cell types detected in every donor. Cell-cluster analysis reveals ~25-30% β-cell reductions consisting of β-cell loss and proportional increases in a senescent β-cell subpopulation in T2D donors, consistent with previous reports. Further, comparative data integration identifies 511 differentially expressed genes (DEGs) in T2D β-cells, including T2D-associated vitamin A metabolism genes, which are linked to impaired β-cell viability by multimodal functional validation. Integration with T2D genetic, proteomic, and mouse model metabolic phenotypes nominates 58 candidate causal T2D genes, including PDZK1 and GRAMD2B, which preserve β-cell mass. Together, this genomic resource provides an enhanced type 2 diabetes expression-atlas for data exploration, analysis, and hypothesis testing, as well as a novel genomic resource for insights into T2D pathophysiology and human islet dysfunction.