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). 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 data sets (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 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.