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

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.

Ubiquitin-Specific Protease 25 Aggravates Acute Pancreatitis and Acute Pancreatitis-Related Multiple Organ Injury by Destroying Tight Junctions Through Activation of The STAT3 Pathway

Ubiquitin-specific protease 25 (USP25) plays an important role in inflammation and immunity. However, the role of USP25 in acute pancreatitis (AP) is still unclear. To evaluate the role of USP25 in AP, we conducted research on clinical AP patients, USP25wild-type(WT)/USP25 knockout (USP25−/−) mice, and pancreatic acinar cells. Our results showed that serum USP25 concentration was higher in AP patients than in healthy controls and was positively correlated with disease severity. AP patients’ serum USP25 levels after treatment were significantly lower than that at the onset of AP. Moreover, USP25 expression was upregulated in cerulein-induced AP in mice, while USP25 deficiency attenuates AP and AP-related multiple organ injury. In vivo and in vitro studies showed that USP25 exacerbates AP by promoting the release of pro-inflammatory factors and destroying tight junctions of the pancreas. We showed that USP25 aggravates AP and AP-related multiple organ injury by activating the signal transducer and activator of transcription 3 (STAT3) pathway. Targeting the action of USP25 may present a potential therapeutic option for treating AP.

Production of Human Pancreatitis-Associated Protein (hPAP) in Komagataella phaffii (Pichia pastoris)

Pancreatitis-associated protein (PAP) is a pancreatic stress protein that is not produced in a healthy pancreas but is highly synthesized in pancreatic acinar cells in response to acute and chronic pancreatitis, hypoxia, toxins, diabetes, lipopolysaccharides hypotransferrinemia and organ transplantation. Changes in the PAP levels in serum are an important biological marker in the early stage of pancreatic diseases. In this study, the recombinant human PAP protein, which has the potential to be used as a diagnostic marker and as research material in proliferation, apoptosis, cell migration, cell invasion, and immunoassay studies, was expressed efficiently under the control of the AOX1 gene promoter in the Komagataella phaffii (Pichia pastoris) (K. phaffii) X33 strain. We describe the conditions required for the efficient production of PAP protein by methanol induction and its use without purification. The produced unpurified protein was tested in sandwich ELISA and showed consistent results with the commercial product. These results are encouraging that the protein produced can be used as a biomarker standard in ELISA tests without the cost and labor of purification.

IRAG2 Interacts with IP3-Receptor Types 1, 2, and 3 and Regulates Intracellular Ca2+ in Murine Pancreatic Acinar Cells

The inositol 1,4,5-triphosphate receptor-associated 2 (IRAG2) is also known as Jaw1 or lymphoid-restricted membrane protein (LRMP) and shares homology with the inositol 1,4,5-triphosphate receptor-associated cGMP kinase substrate 1 (IRAG1). IRAG1 interacts with inositol trisphosphate receptors (IP3 receptors /IP3R) via its coiled-coil domain and modulates Ca2+ release from intracellular stores. Due to the homology of IRAG1 and IRAG2, especially in its coiled-coil domain, it is possible that IRAG2 has similar interaction partners like IRAG1 and that IRAG2 also modulates intracellular Ca2+ signaling. In our study, we localized IRAG2 in pancreatic acinar cells of the exocrine pancreas, and we investigated the interaction of IRAG2 with IP3 receptors and its impact on intracellular Ca2+ signaling and exocrine pancreatic function, like amylase secretion. We detected the interaction of IRAG2 with different subtypes of IP3R and altered Ca2+ release in pancreatic acinar cells from mice lacking IRAG2. IRAG2 deficiency decreased basal levels of intracellular Ca2+, suggesting that IRAG2 leads to activation of IP3R under unstimulated basal conditions. Moreover, we observed that loss of IRAG2 impacts the secretion of amylase. Our data, therefore, suggest that IRAG2 modulates intracellular Ca2+ signaling, which regulates exocrine pancreatic function.

Glycoprotein 2 in health and disease: lifting the veil

In 2020, we discovered glycoprotein 2 (GP2) variants associated with pancreatic cancer susceptibility in a genome-wide association study involving the Japanese population. Individuals carrying a missense coding variant (rs78193826) in the GP2 gene resulting in a p.V432M substitution had an approximately 1.5-fold higher risk of developing pancreatic cancer than those without this variant. GP2 is expressed on the inner surface of zymogen granules in pancreatic acinar cells, which are responsible for the sorting, storage and secretion of digestive enzymes. Upon neuronal, hormonal, or other stimulation, GP2 is cleaved from the membrane of zymogen granules and then secreted into the pancreatic duct and intestinal lumen. While the functions of GP2 remain poorly understood, emerging evidence suggests that it plays an antibacterial role in the gastrointestinal tract after being secreted from pancreatic acinar cells. Impaired GP2 functions may facilitate the adhesion of bacteria to the intestinal mucosa. In this review article, we summarize the role of GP2 in health and disease, emphasizing its functions in the gastrointestinal tract, as well as genetic variations in the GP2 gene and their associations with disease susceptibility. We hope that its robust genetic associations with pancreatic cancer, coupled with its emerging role in gastrointestinal mucosal immunity, will spur renewed research interest in GP2, which has been understudied over the past 30 years compared with its paralog uromodulin (UMOD).

Counter effects of Vitamin E against Outcomes of Alcohol Toxicity in Pancreatic Acini: Histomorphometric Study

Aim: To evaluate the effects of alcohol on the microscopic morphology of the exocrine pancreas and blood serum amylase and to explored that if vitamin E has a protective role against alcohol-induced damage in the pancreas of rabbits. Study design: Analytical experimental study Place and duration of study: Departments of Anatomy, Pathology and Pharmacology in Peshawar Medical College Pakistan from 1st January 2019 to 30th June 2019. Methodology: Eighteen healthy adult male domestic rabbits weighing 1-1.5 kg were chosen (oryctolaguscuniculus). The control group A received proper food and normal saline as drinking water, experimental group B received proper diet and 30 percent ethanol solution (30ml/kg/day) orally daily with normal saline, and experimental group C received proper diet, 30 percent ethanol solution (30ml/kg/day), vitamin E (50mg/kg/day) orally daily with normal saline. Each rabbit's blood was taken for serum amylase. Morphology of acinar cells included: 1) number of cells, (10 acini/field, 2) size of acini, 3) size of acinar cells, and 4) size of acinar nuclei. Results: Normal value of serum amylase in rabbits was found. The difference in serum amylase levels between the control and experimental groups for both E4 and E8 animals was not statistically significant. There was no significant difference in the number of pancreatic acinar cells, size of pancreatic acini, the pancreatic acinar cell size, and pancreatic acinar cells nuclear size in the control and experimental groups for both E4 and E8 animals. Conclusion: Alcohol consumption had no influence on the histomorphology of the rabbits' pancreatic acini in a short period (4-8 weeks). No significant variation was noted in the pancreatic acinar cells count & size, pancreatic acinar cells nuclear count and size, and pancreatic acini size. Therefore, protective role of vitamin E was not usefully identified. Keywords: Alcohol, Pancreas, Histomorphology, Vitamin E, Serum amylase

ELAPOR1 is a secretory granule maturation-promoting factor that is lost during paligenosis

A single transcription factor, MIST1 (BHLHA15), maximizes secretory function in diverse secretory cells (like pancreatic acinar cells) by transcriptionally upregulating genes that elaborate secretory architecture. Here, we show that the scantly-studied MIST1 target, ELAPOR1, is an evolutionarily conserved, novel Mannose-6-phosphate receptor (M6PR) domain-containing protein. ELAPOR1 expression was specific to zymogenic cells (ZCs, the MIST1-expressing population in the stomach). ELAPOR1 expression was lost as tissue injury caused ZCs to undergo paligenosis (ie, to become metaplastic and reenter the cell cycle). In cultured cells, ELAPOR1 trafficked with cis-Golgi resident proteins and with the trans-Golgi and late endosome protein: cation-independent M6PR. Secretory vesicle trafficking was disrupted by expression of ELAPOR1 truncation mutants. Mass spectrometric analysis of co-immunoprecipitated proteins showed ELAPOR1 and CI-M6PR shared many binding partners. However, CI-M6PR and ELAPOR1 must function differently, as CI-M6PR co-immunoprecipitated more lysosomal proteins and was not decreased during paligenosis in vivo. We generated Elapor1−/− mice to determine ELAPOR1 function in vivo. Consistent with in vitro findings, secretory granule maturation was defective in Elapor1−/− ZCs. Our results identify a role for ELAPOR1 in secretory granule maturation and help clarify how a single transcription factor maintains mature exocrine cell architecture in homeostasis and helps dismantles it during paligenosis.

Kynurenic Acid and Its Analogue SZR-72 Ameliorate the Severity of Experimental Acute Necrotizing Pancreatitis

The pathophysiology of acute pancreatitis (AP) is not well understood, and the disease does not have specific therapy. Tryptophan metabolite L-kynurenic acid (KYNA) and its synthetic analogue SZR-72 are antagonists of the N-methyl-D-aspartate receptor (NMDAR) and have immune modulatory roles in several inflammatory diseases. Our aims were to investigate the effects of KYNA and SZR-72 on experimental AP and to reveal their possible mode of action. AP was induced by intraperitoneal (i.p.) injection of L-ornithine-HCl (LO) in SPRD rats. Animals were pretreated with 75-300 mg/kg KYNA or SZR-72. Control animals were injected with physiological saline instead of LO, KYNA and/or SZR-72. Laboratory and histological parameters, as well as pancreatic and systemic circulation were measured to evaluate AP severity. Pancreatic heat shock protein-72 and IL-1β were measured by western blot and ELISA, respectively. Pancreatic expression of NMDAR1 was investigated by RT-PCR and immunohistochemistry. Viability of isolated pancreatic acinar cells in response to LO, KYNA, SZR-72 and/or NMDA administration was assessed by propidium-iodide assay. The effects of LO and/or SZR-72 on neutrophil granulocyte function was also studied. Almost all investigated laboratory and histological parameters of AP were significantly reduced by administration of 300 mg/kg KYNA or SZR-72, whereas the 150 mg/kg or 75 mg/kg doses were less or not effective, respectively. The decreased pancreatic microcirculation was also improved in the AP groups treated with 300 mg/kg KYNA or SZR-72. Interestingly, pancreatic heat shock protein-72 expression was significantly increased by administration of SZR-72, KYNA and/or LO. mRNA and protein expression of NMDAR1 was detected in pancreatic tissue. LO treatment caused acinar cell toxicity which was reversed by 250 µM KYNA or SZR-72. Treatment of acini with NMDA (25, 250, 2000 µM) did not influence the effects of KYNA or SZR-72. Moreover, SZR-72 reduced LO-induced H2O2 production of neutrophil granulocytes. KYNA and SZR-72 have dose-dependent protective effects on LO-induced AP or acinar toxicity which seem to be independent of pancreatic NMDA receptors. Furthermore, SZR-72 treatment suppressed AP-induced activation of neutrophil granulocytes. This study suggests that administration of KYNA and its derivative could be beneficial in AP.