Long-term culture of human pancreatic islets reveals reduced metal ion pathways in their gene signature

Pancreatic islet transplantation is an effective therapy for type 1 diabetes; however, its broader clinical application is limited by the shortage of donors. Establishing long-term culture methods for isolated islets is an area of ongoing investigation that may ultimately support applications such as biobanking and stem cell–derived islets. However, maintaining transplantable quality of islets during extended culture remains a challenge. We recently developed a method for human islet culture on optimally sized microwells that preserves viability over two weeks. Despite improved viability, other key pre-transplantation factors, such as islet metabolism, remained reduced, indicating a need for further optimization. To identify potential targets for improvement, we performed RNA sequencing on human islets from three deceased donors, comparing two-week cultures (microwell and conventional) versus pre-culture controls. Transcriptomic analysis showed significant gene expression changes in two-week-cultured islets compared to pre-culture islets, whereas microwell and conventional culture conditions showed minimal differences despite improved viability in microwell culture. Pathway analysis revealed that long-term culture consistently downregulates heavy metal ion–related pathways, particularly zinc-related pathways regulated by metallothioneins. This suggests a loss of β-cell characteristics during extended culture. Our findings highlight intra-islet metal ion homeostasis as a potential therapeutic target for improving transplantation outcomes following prolonged islet culture.