Heterogeneous expression patterns of the T2D-associated kinesin-4 KIF21A in pancreatic islet endocrine cells

The β cells in the pancreatic endocrine islets preferentially secrete insulin in specific subdomains of the plasma membrane adjacent to the vasculature (i.e., hot spots). Impaired insulin secretion and β -cell dysfunction are central features of Type-2 Diabetes, yet the cytoskeletal machinery that supports directional secretion and secretory hot spots remains incompletely defined. KIF21A is a plus-end-directed kinesin-4 motor protein that anchors microtubule plus ends to the cell cortex. However, the role of KIF21A in pancreatic islet endocrine cells and potential link to type 2 diabetes (T2D) remain unexplored.

KIF21A mRNA and protein levels were analyzed using bulk RNA-seq and single-cell RNA-seq data using proteomics databases. Kif21a protein distribution was assessed by immunofluorescence in isolated mouse islets using super-resolution microscopy. Likewise, immunostaining of insulin, glucagon, somatostatin, laminin, and detyrosinated tubulin is also performed.

We show that KIF21A is downregulated in T2D human islets at both the mRNA (RNA-seq) and protein (quantitative proteomics) levels. We also demonstrate cell-type-specific enrichment of Kif21a protein (δ > α > β) in intact islets, confirming the hierarchy suggested by single-cell transcriptomics. We also show that within each endocrine lineage, Kif21a protein shows pronounced cell-to-cell heterogeneity, consistent with endocrine sub-states and functional specialization. And most importantly, we show that implicating Kif21a is spatially enriched at the rosettes and laminin-rich interfaces at vasculature-oriented secretion sites (hot spots), where microtubule anchoring is expected to shape targeted granule delivery.

KIF21A is a T2D-associated gene with cell-type-specific and heterogeneous expression in islet endocrine cells. KIF21A may have a cortical microtubule-anchoring function and may contribute to the directed granule delivery to the vasculature for regulated hormone secretion.