Mesenchymal Wt1 positive stellate cells represent a minor source of the fibrotic response in pancreatitis

Severe pancreatitis is accompanied by a strong fibrotic response characterized through the presence of activated myofibroblasts. Beside hematopoietic stem cells and resident fibroblasts, pancreatic stellate cells are traded as the main cell population giving rise to activated myofibroblasts. The origin of myofibroblasts is highly under debate and so far not successfully clarified. In vivo evidences that stellate cells are predominantly responsible for the stromal reaction are still missing. Therefore, we performed lineage-tracing experiments of pancreatic stellate cells in Wt1Cre^ERT2;LSL-td-Tomato mice and analyzed the fibrotic response after caerulein treatment and pancreatic duct ligation. Wt1 positive cell identity, localization and quantification were determined with immunohistochemistry and immunofluorescence staining as well as FACS analyses. We identified a periacinar stellate cell population which is positive for Wt1Cre expression. Induction of cerulein-mediated pancreatitis associated with a fibrotic reaction lead to a slightly elevated number of Wt1 positive cells. However, Wt1 positive cells represent only a minor cell population of alpha-Sma positive myofibroblasts. Nevertheless, isolated pancreatic fibroblasts from cerulein-treated mice show an elevated number of Wt1 positive cells compared to untreated control mice and a strong myofibroblast activation of Wt1 positive cells is discovered at least under cell culture conditions. Based on our lineage tracing data, we consider that Wt1-positive pancreatic stellate cells represent merely a minor source of mesenchymal cells, which are responsible for the fibrotic reaction in vivo. However, the Wt1 positive stellate cells demonstrate a high capacity of myofibroblast formation in vitro.