Identification of a vimentin-expressing α-cell phenotype in CF and normal pancreas

Endocrine dysfunction and diabetes can develop secondary to fibrotic diseases within the pancreas, including cystic fibrosis (CF). A phenotypic shift within epithelial cells has been recognised in association with pro-fibrotic signalling. We sought evidence of endocrine cell epithelial-to-mesenchymal transition in CF and non-CF pancreas. Post-mortem pancreatic sections from 24 people with CF and 10 organ donors without CF or diabetes were stained for insulin/glucagon/vimentin and Sirius red/fast green with collagen distribution assessed semi-quantitatively (CF) and quantitatively (non-CF). Analysis of existing single-cell RNA-sequencing datasets (three adult donors without diabetes and nine with chronic pancreatitis) for α-cell vimentin expression was performed. Cells co-expressing glucagon/vimentin were detected in a proportion (32(4,61)% (median (Q1,Q3))) of islets in all CF pancreata except donors dying perinatally. CF histopathology was characterised by peri-islet fibrosis, and 60(45,80)% of islets were surrounded by collagen strands. A positive correlation between islet fibrosis and vimentin-expressing α-cells was seen in non-CF donors <31 years (r = 0.972; P = 0.006). A possible association with donor age was seen in all donors (r = 0.343; P = 0.047). Single-cell RNA-sequencing analysis of isolated islets from non-diabetic donors and donors with chronic pancreatitis confirmed the presence of vimentin-positive and vimentin-negative α-cells. Differentiated α-cell function-associated gene expression was maintained. Differentially upregulated processes in co-expressing cells included pathways associated with extracellular matrix organisation, cell-cell adhesion, migratory capability and self-renewal. We have identified and characterised an intermediate epithelial/mesenchymal state in a sub-population of α-cells present throughout post-natal life, which may play a role in their response to extrinsic stressors, including fibrosis and ageing.