Cryopreserved mouse pancreatic acinar cells from long-term explant outgrowth cultures maintain their secretory phenotype after thawing

Regulation of p38 MAPK and glucocorticoid receptor activation by hydrocortisone in mono-and co-cultured pancreatic acinar and stellate cells

BACKGROUND/OBJECTIVES

Acute pancreatitis develops as an inflammatory response to pancreatic tissue injury. Postoperative pancreatitis has recently been associated with increased occurrence of complications. Activation of the mitogen-activated protein kinase p38 (p38 MAPK) pathway occurs early in acute pancreatitis and its inhibition has been suggested to alleviate pancreatic inflammation. Glucocorticoids are potent anti-inflammatory steroids whose use in the management of acute pancreatitis remains controversial. Our aim was to examine the effect of crosstalk between pancreatic acinar cells (PACs) and stellate cells (PSCs) on p38 MAPK and glucocorticoid receptor (GR) activation and to assess the impact of hydrocortisone on these events.

METHODS

The long-term co-culture setting for mouse PACs and PSCs developed in our laboratory was used. Parallel 4d mono- and co-cultures with or without 10 nM hydrocortisone were performed followed by immunocytochemical analysis of nuclear GR and phospho-p38 MAPK (pp38 MAPK).

RESULTS

Hydrocortisone inhibited pp38 MAPK up-regulation evoked by co-culture in PACs and PSCs and increased nuclear translocation of GR in PAC monocultures and in co-cultured PACs and PSCs. In PSC monocultures and co-cultured PACs, ligand-independent expression of nuclear GR was observed. In the former no change in nuclear GR but a significant decrease in total GR as analyzed by Western blot was caused by hydrocortisone.

CONCLUSIONS

Cellular microenvironment plays a significant role on p38 MAPK and GR activation in PACs and PSCs. Hydrocortisone is an effective means to inhibit p38 MAPK activation in PACs and PSCs. Both ligand-dependent and -independent regulatory roles for GR are suggested in the exocrine pancreas.

Wnt/β-catenin signalling plays diverse functions during the process of fibrotic remodelling in the exocrine pancreas

BACKGROUND/OBJECTIVES

Wnt/β-catenin signalling plays vital roles in tissue homeostasis. Dysregulation of the pathway has been implicated in the pathogenesis of cancer and fibroses in numerous tissues, including the pancreas. We studied the effect of microenvironmental changes pertaining to fibrotic tissue remodelling on the expression of selected Wnt/β-catenin pathway proteins in the human exocrine pancreas. The role of acinar/stellate cross-talk on the expression of the proteins was elucidated in a long-term mouse co-culture system.

METHODS

Expression of β-catenin, Wnt2, Wnt5a and SFRP4 was analysed immunohistochemically in normal and moderately or highly fibrotic human pancreata (n = 8). The effect of humoral interactions on the expression of the proteins was studied by immunocytochemical means in parallel mono- and co-cultures of mouse acinar and stellate cells (PSCs).

RESULTS

In human pancreatic tissue, fibrotic microenvironment was associated with redistribution of the proteins in and between epithelial and stromal compartments, compared to acinar-rich tissue. In non-fibrotic and moderately fibrotic tissue the proteins appeared only in acinar cells whereas in highly fibrotic tissue stromal fibroblastoid/stellate cells and macrophages were their predominant locations. Subcellular changes in the expression of β-catenin and Wnt5a were detected. Our in vitro data suggest potential involvement of acinar cell/PSC cross-talk in mediating the changes observed in tissue specimens.

CONCLUSIONS

Wnt/β-catenin pathway-associated proteins are abundantly expressed in the exocrine pancreas with prominent changes in their cellular and subcellular expression patterns along with increasing levels of fibrosis. Diverse functions for Wnt/β-catenin signalling during the course of fibrotic remodelling in the exocrine pancreas are suggested.

Reciprocal stimulation of pancreatic acinar and stellate cells in a novel long-term in vitro co-culture model

BACKGROUND/OBJECTIVES

Pancreatic stellate cells (PSCs) are the key fibrogenic cells in the pancreas. Acinar cell injury is known to trigger PSC activation. To facilitate the experimental analysis of the crosstalk between acinar cells and PSCs, an in vitro system for their long-term co-cultivation was developed.

MATERIALS AND METHODS

PSCs and acinar cells capable of retaining their secretory phenotype in long-term in vitro culture were obtained from mouse pancreata. A dual-chamber co-culture model was built in 24-well format with acinar cells seeded in the wells and PSCs in tissue culture inserts. Acinar cell-3T3 fibroblast co-cultures served as controls. After 4-day maintenance, the acinar compartment was analyzed for cell morphology, secretory capability, necrosis (HMGB1), apoptosis (TUNEL) and inflammation (NFκB). PSCs were analyzed for migratory activity and extracellular matrix (ECM) protein expression. The results were compared to parallel monocultures.

RESULTS

Acinar cells in monoculture and in co-culture with fibroblasts exhibited a healthy monolayer arrangement and an ability to respond to 0.1 nM caerulein stimulus by increased amylase release. Co-culture with PSCs caused marked changes in acinar cell morphology and rendered them insensitive to secretagogue stimulus. Activation of NFκB and necrotic changes, but not apoptosis, were identified in co-cultured acinar cells. Co-culture increased the migratory activity and ECM protein expression of PSCs.

CONCLUSIONS

Humoral interactions between acinar and PSCs in co-culture were shown to reciprocally affect their cellular functions. With its two separable cell compartments the co-culture system provides a versatile culture setting that allows independent manipulation and analysis of both cell types.

Notch Signaling in Pancreatic Development

The Notch signaling pathway plays a significant role in embryonic cell fate determination and adult tissue homeostasis. Various studies have demonstrated the deep involvement of Notch signaling in the development of the pancreas and the lateral inhibition of Notch signaling in pancreatic progenitor differentiation and maintenance. The targeted inactivation of the Notch pathway components promotes premature differentiation of the endocrine pancreas. However, there is still the contrary opinion that Notch signaling specifies the endocrine lineage. Here, we review the current knowledge of the Notch signaling pathway in pancreatic development and its crosstalk with the Wingless and INT-1 (Wnt) and fibroblast growth factor (FGF) pathways.