MFG-E8 Maintains Cellular Homeostasis by Suppressing Endoplasmic Reticulum Stress in Pancreatic Exocrine Acinar Cells.

Yifan Ren,Yuanyuan Zhang,Jia Zhang,Jianbin Bi,Yi Lv,Zheng Wu,Wuming Liu,Meng Fan,Rongqian Wu

doi:10.3389/fcell.2021.803876

Abstract

Excessive endoplasmic reticulum (ER) stress contributes significantly to the pathogenesis of exocrine acinar damage in acute pancreatitis. Our previous study found that milk fat globule EGF factor 8 (MFG-E8), a lipophilic glycoprotein, alleviates acinar cell damage during AP via binding to αvβ3/5 integrins. Ligand-dependent integrin-FAK activation of STAT3 was reported to be of great importance for maintaining cellular homeostasis. However, MFG-E8’s role in ER stress in pancreatic exocrine acinar cells has not been evaluated. To study this, thapsigargin, brefeldin A, tunicamycin and cerulein + LPS were used to induce ER stress in rat pancreatic acinar cells in vitro. L-arginine- and cerulein + LPS-induced acute pancreatitis in mice were used to study ER stress in vivo. The results showed that MFG-E8 dose-dependently inhibited ER stress under both in vitro and in vivo conditions. MFG-E8 knockout mice suffered more severe ER stress and greater inflammatory response after L-arginine administration. Mechanistically, MFG-E8 increased phosphorylation of FAK and STAT3 in cerulein + LPS-treated pancreatic acinar cells. The presence of specific inhibitors of αvβ3/5 integrin, FAK or STAT3 abolished MFG-E8’s effect on cerulein + LPS-induced ER stress in pancreatic acinar cells. In conclusion, MFG-E8 maintains cellular homeostasis by alleviating ER stress in pancreatic exocrine acinar cells.

Highlights

Endoplasmic reticulum (ER) stress is involved in the damage of pancreatic exocrine acinar cells in acute pancreatitis (Sun et al, 2019; Tan et al, 2020)
The expression levels of glucose-regulated protein 78 (GRP78), phospho-inositol-requiring enzyme 1 α (IRE1α) and C/EBP homologous protein (CHOP) in cells of the rat exocrine pancreas (AR42J) cells showing a gradual increase in the increase of tunicamycin (p < 0.05, Figures 1D–F) and brefeldin A (p < 0.05, Figures 1G–I) doses
We added 20 ng/ml and 100 ng/ml of recombinant MFG-E8 to AR42J cells treated with 5 nM thapsigargin, 1 μM tunicamycin, and 6 μg/ml brefeldin A, respectively

Summary

Introduction

Endoplasmic reticulum (ER) stress is involved in the damage of pancreatic exocrine acinar cells in acute pancreatitis (Sun et al, 2019; Tan et al, 2020). Inositol-required enzyme 1 (IRE1)-XBP1, PKR-like endoplasmic reticulum kinase (PERK), eukaryotic initiation factor 2 alpha (eIF2α), activating transcription factor 6 (ATF6), and binding immunoglobulin protein (BIP, known as glucose-regulated protein 78-kDa, GRP78) are the main signaling pathways that mediate the development of ER stress (Jiang et al, 2010; He, 2021; You et al, 2021). ER stress induced by different causes activates these pathways, respectively or simultaneously, and leads to the unfolded protein response (UPR). Under excessive ER stress conditions, UPR could not further alleviate cellular damage, but instead accelerate cell death by inducing the activation of apoptosis-related molecules transcription factor C/EBP homologous protein (CHOP) and caspase-9 (Gorman et al, 2012). When ER stress occurs, IRE1α recruits TRAF2 into ER and initiates the inflammatory response via activating the NF-κB pathway (Keestra-Gounder et al, 2016). The storm of the inflammatory response sweeps through the affected organs, and induces systemic damage, resulting in multiple organ injury

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