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

Introduction:

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.

Aim:

The aim of the project was the lineage tracing of pancreatic stellate cells.

Methods:

We performed lineage-tracing experiments 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.

Results:

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 indicating that Wt1-positive cells represent only a minor cell population of alpha-Sma positive myofibroblasts. However, after duct ligation an increasing number of Wt1-positive cells can be found in the myofibroblast population. 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 under cell culture conditions.

Conclusions:

Based on our lineage tracing data, we consider that Wt1-positive pancreatic stellate cells represent a source of mesenchymal cells, which are responsible for the fibrotic reaction in vivo. However, the quantity of Wt1-positive cells in the myofibroblast population highly depends on the model of fibrosis. Similarly, Wt1-positive stellate cells demonstrate a high capacity of myofibroblast formation in vitro.