Meflin is a marker of pancreatic stellate cells involved in fibrosis and epithelial regeneration in the pancreas

Abstract Pancreatic stellate cells (PSCs) are stromal cells in the pancreas that play an important role in pancreatic pathology. In chronic pancreatitis (CP) and pancreatic ductal adenocarcinoma (PDAC), PSCs are known to get activated to form myofibroblasts or cancer‐associated fibroblasts (CAFs) that promote stromal fibroinflammatory reactions. However, previous studies on PSCs were mainly based on the findings obtained using ex vivo expanded PSCs, with few studies that addressed the significance of in situ tissue‐resident PSCs using animal models. Their contributions to fibrotic reactions in CP and PDAC are also lesser‐known. These limitations in our understanding of PSC biology have been attributed to the lack of specific molecular markers of PSCs. Herein, we established Meflin ( Islr ), a glycosylphosphatidylinositol‐anchored membrane protein, as a PSC‐specific marker in both mouse and human by using human pancreatic tissue samples and Meflin reporter mice. Meflin‐positive (Meflin + ) cells contain lipid droplets and express the conventional PSC marker Desmin in normal mouse pancreas, with some cells also positive for Gli1, the marker of pancreatic tissue‐resident fibroblasts. Three‐dimensional analysis of the cleared pancreas of Meflin reporter mice showed that Meflin + PSCs have long and thin cytoplasmic protrusions, and are localised on the abluminal side of vessels in the normal pancreas. Lineage tracing experiments revealed that Meflin + PSCs constitute one of the origins of fibroblasts and CAFs in CP and PDAC, respectively. In these diseases, Meflin + PSC‐derived fibroblasts showed a distinctive morphology and distribution from Meflin + PSCs in the normal pancreas. Furthermore, we showed that the genetic depletion of Meflin + PSCs accelerated fibrosis and attenuated epithelial regeneration and stromal R‐spondin 3 expression, thereby implying that Meflin + PSCs and their lineage cells may support tissue recovery and Wnt/R‐spondin signalling after pancreatic injury and PDAC development. Together, these data indicate that Meflin may be a marker specific to tissue‐resident PSCs and useful for studying their biology in both health and disease. © 2023 The Pathological Society of Great Britain and Ireland.