scRNA-seq of canine insulinoma
Canine malignant insulinoma is a rare, highly metastatic and life-threatening neuroendocrine tumour of pancreatic beta cells. To map the single-cell transcriptomic landscape of canine insulinoma for the first time, transcriptomic profiles of 5,532 cells were captured from two spontaneous insulinomas (Patient 1 and 2) and one associated metastasis (Patient 2) in two Boxer dogs. Distinct cancer, endocrine, and immune cell populations were identified. Notably, all three tumour samples contained two transcriptionally distinct insulin-expressing tumour cell populations (INS+ and INS+ FOSlow), characterised here for the first time. These two cancer cell populations significantly differed by ~8,000 differentially expressed genes (DEGs), particularly tumour suppressor genes (e.g. TP53, EGR1) and cancer-related pathways (e.g., MAPK, p53). In contrast, COX7A2L was one of a few genes ubiquitously expressed and significantly upregulated (>20-fold) in both insulin-expressing tumour populations compared to other captured populations. Both populations were also characterised by expression of chromogranin/secretogranin neuroendocrine tumour marker genes (e.g. CHGA SCGN). There were far fewer gene expression differences observed between insulin-expressing tumour cells from the two patients (~600 DEGs) than between the two cancer cell populations within each patient. These DEGs included CLTRN, TMSB4X, CSRP2, LGALS2, and C15orf48. Unexpectedly for a tumour of endocrine origin, the metastasis in Patient 2 exhibited >20-70 fold upregulation of exocrine pancreatic genes including CLPS, PRSS2, PRSS and CTRC. Immune cell analyses identified distinct infiltrating immune populations, including memory T cells and macrophages and revealed likely tumour-immune interactions, including the CD40-CD40L interaction.  This study provides the first single-cell RNA sequencing (scRNA-seq) analysis of naturally occurring insulinoma in any species, revealing tumour cell heterogeneity, novel immune microenvironment features, and potential therapeutic targets. Despite its small scale, the findings highlight the utility of scRNA-seq in veterinary oncology and its translational potential for pancreatic neuroendocrine tumours across species.