Human CPA1 mutation causes digestive enzyme misfolding and chronic pancreatitis in mice

Genetic Variability in the CPA1 Gene and Its Impact on Acute Pancreatitis Risk: New Insights from a Large-Scale Study

Acute pancreatitis (AP) is a common and potentially lethal disease. Over the last 10 years, AP has become one of the most important healthcare problems. On a global scale, the incidence has increased by 63% over the last 20 years. AP is usually caused by gallstones and excessive alcohol consumption and genetic factors play an important role in the development of inflammation. Recent studies involving the CPA1 mutations are ambiguous and dependent on the population studied. In this study, the variability of the CPA1 gene in patients with AP was analyzed. Genetic material was isolated from the blood of 301 patients with AP and 184 healthy individuals. Identification of the variants in exons 5, 6, 8, and 9 with introns was performed using molecular biology methods. Mutations were identified by comparison to the reference sequence (NM_001868.4). Statistical analysis included the identification of mutations correlating with the risk of AP, the etiology of inflammation, and family history. Several novel mutations in the CPA1 gene have been identified, along with a high degree of variability within the coding region of the carboxypeptidase gene. A correlation between mutations CPA1:c.1072 + 84del; c.987 + 57G>A and increased risk of developing AP was found. Two protective mutations, CPA1:c.625A>T, c.1072 + 94del, were identified. The CPA1 gene is characterized by high sequence variability and regions in which mutations lead to an increased risk of developing AP. Single or co-occurring mutations of the CPA1 gene can significantly affect the risk of developing AP.

Modeling protease-sensitive human pancreatic lipase mutations in the mouse ortholog

Pancreatic lipase (PNLIP) is the major lipolytic enzyme secreted by the pancreas. A recent study identified human PNLIP variants P245A, I265R, F300L, S304F, and F314L in European cohorts with chronic pancreatitis. Functional analyses indicated that the variants were normally secreted but exhibited reduced stability when exposed to pancreatic proteases. Proteolysis of the PNLIP variants yielded an intact C-terminal domain, while the N-terminal domain was degraded. The protease-sensitive PNLIP phenotype was strongly correlated with chronic pancreatitis, suggesting a novel pathological pathway underlying the disease. To facilitate preclinical mouse modeling, here we investigated how the human mutations affected the secretion and proteolytic stability of mouse PNLIP. We found that variants I265R, F300L, S304F, and F314L were secreted at high levels, while P245A had a secretion defect and accumulated inside the cells. Proteolysis experiments indicated that wild-type mouse PNLIP was resistant to cleavage, while variant I265R was readily degraded by mouse trypsin and chymotrypsin C. Variants F300L, S304F, and F314L were unaffected by trypsin but were slowly proteolyzed by chymotrypsin C. The proteases degraded the N-terminal domain of variant I265R, leaving the C-terminal domain intact. Structural analyses suggested that changes in stabilizing interactions around the I265R mutation site contribute to the increased proteolytic susceptibility of this variant. The results demonstrate that variant I265R is the best candidate for modeling the protease-sensitive PNLIP phenotype in mice.

Novel chymotrypsin C (CTRC) variants from real-world genetic testing of pediatric chronic pancreatitis cases

BACKGROUND

Chymotrypsin C (CTRC) protects the pancreas against unwanted intrapancreatic trypsin activity through degradation of trypsinogen. Loss-of-function CTRC variants increase the risk for chronic pancreatitis (CP). The aim of the present study was to characterize novel CTRC variants found during genetic testing of CP cases at a pediatric pancreatitis center.

METHODS

We used next-generation sequencing to screen patients. We analyzed the functional effects of CTRC variants in HEK 293T cells and using purified enzymes.

RESULTS

In 5 separate cases, we detected 5 novel heterozygous CTRC variants: c.407C>T (p.Thr136Ile), c.550G>A (p.Ala184Thr), c.627Cdup (p.Ser210Leufs∗?, where the naming indicates a frame shift with no stop codon), c.628T>C (p.Ser210Pro), and c.779A>G (p.Asp260Gly). Functional studies revealed that with the exception of p.Ser210Leufs∗?, the CTRC variants were secreted normally from transfected cells. Enzyme activity of purified variants p.Thr136Ile, p.Ala184Thr, and p.Asp260Gly was similar to that of wild-type CTRC, whereas variant p.Ser210Pro was inactive. The frame-shift variant p.Ser210Leufs∗? was not secreted but accumulated intracellularly, and induced endoplasmic reticulum stress, as judged by elevated mRNA levels of HSPA5 and DDIT3, and increased mRNA splicing of XBP1.

CONCLUSIONS

CTRC variants p.Ser210Pro and p.Ser210Leufs∗? abolish CTRC function and should be classified as pathogenic. Mechanistically, variant p.Ser210Pro directly affects the amino acid at the bottom of the substrate-binding pocket while the frame-shift variant promotes misfolding and thereby blocks enzyme secretion. Importantly, 3 of the 5 novel CTRC variants proved to be benign, indicating that functional analysis is indispensable for reliable determination of pathogenicity and the correct interpretation of genetic test results.

A common CTRB misfolding variant associated with pancreatic cancer risk causes ER stress and inflammation in mice

Objective

Genome wide association studies have identified an exon 6 CTRB2 deletion variant that associates with increased risk of pancreatic cancer. To acquire evidence on its causal role, we developed a new mouse strain carrying an equivalent variant in Ctrb1 , the mouse orthologue of CTRB2 .

Design

We used CRISPR/Cas9 to introduce a 707bp deletion in Ctrb1 encompassing exon 6 ( Ctrb1 Δexon6 ). This mutation closely mimics the human deletion variant. Mice carrying the mutant allele were extensively profiled at 3 months to assess their phenotype.

Results

Ctrb1 Δexon6 mutant mice express a truncated CTRB1 that accumulates in the ER. The pancreas of homozygous mutant mice displays reduced chymotrypsin activity and total protein synthesis. The histological aspect of the pancreas is inconspicuous but ultrastructural analysis shows evidence of dramatic ER stress and cytoplasmic and nuclear inclusions. Transcriptomic analyses of the pancreas of mutant mice reveals acinar program down-regulation and increased activity of ER stress-related and inflammatory pathways. Heterozygous mice have an intermediate phenotype. Agr2 is one of the most up-regulated genes in mutant pancreata. Ctrb1 Δexon6 mice exhibit impaired recovery from acute caerulein-induced pancreatitis. Administration of TUDCA or sulindac partially alleviates the phenotype. A transcriptomic signature derived from the mutant pancreata is significantly enriched in normal human pancreas of CTRB2 exon 6 deletion variant carriers from the GTEx cohort.

Conclusions

This mouse strain provides formal evidence that the Ctrb1 Δexon6 variant causes ER stress and inflammation in vivo , providing an excellent model to understand its contribution to pancreatic ductal adenocarcinoma development and to identify preventive strategies.

SUMMARY BOX

What is already known about this subject?: - CTRB2 is one of the most abundant proteins produced by human pancreatic acinar cells. - A common exon 6 deletion variant in CTRB2 has been associated with an increased risk of pancreatic ductal adenocarcinoma. - Misfolding of digestive enzymes is associated with pancreatic pathology.What are the new findings?: - We developed a novel genetic model that recapitulates the human CTRB2 deletion variant in the mouse orthologue, Ctrb1 . - Truncated CTRB1 misfolds and accumulates in the ER; yet, mutant mice display a histologically normal pancreas at 3 months age.- CTRB1 and associated chaperones colocalize in the ER, the cytoplasm, and the nucleus of acinar cells.- Transcriptomics analysis reveals reduced activity of the acinar program and increased activity of pathways involved in ER stress, unfolded protein response, and inflammation.- Mutant mice are sensitized to pancreatic damage and do not recover properly from a mild caerulein-induced pancreatitis.- TUDCA administration partially relieves the ER stress in mutant mice.How might it impact on clinical practice in the foreseeable future?: - The new mouse model provides a tool to identify the mechanisms leading to increased pancreatic cancer risk in CTRB2 exon 6 carriers. - The findings suggest that drugs that cause ER stress relief and/or reduce inflammation might provide preventive opportunities.

Exploring the enigmatic association between PNLIP variants and risk of chronic pancreatitis in a large Chinese cohort

BACKGROUND & AIMS

Protease-sensitive PNLIP variants were recently associated with chronic pancreatitis (CP) in European populations. The pathological mechanism yet remains elusive. Herein, we performed a comprehensive genetic and functional analysis of PNLIP variants found in a large Chinese cohort, aiming to further unravel the enigmatic association of PNLIP variants with CP.

METHODS

All coding and flanking intronic regions of the PNLIP gene were analyzed for rare variants by targeted next-generation sequencing in 1082 Chinese CP patients and 1196 controls. All novel missense variants were subject to analysis of secretion, lipase activity, and proteolytic degradation. One variant was further analyzed for its potential to misfold and induce endoplasmic reticulum (ER) stress. p.F300L, the most common PNLIP variant associated with CP, was used as a control.

RESULTS

We identified 12 rare heterozygous PNLIP variants, with 10 being novel. The variant carrier frequency did not differ between the groups. Of them, only the variant p.A433T found in a single patient was considered pathologically relevant. p.A433T exhibited increased susceptibility to proteolytic degradation, which was much milder than p.F300L. Interestingly, both variants exhibited an increased tendency to misfold, leading to intracellular retention as insoluble aggregates, reduced secretion, and elevated ER stress.

CONCLUSIONS

Our genetic and functional analysis of PNLIP variants identified in a Chinese CP cohort suggests that the p.A433T variant and the previously identified p.F300L variant are not only protease-sensitive but also may be potentially proteotoxic. Mouse studies of the PNLIP p.F300L and p.A433T variants are needed to clarify their role in CP.

GGT1 is a SNP eQTL gene involved in STAT3 activation and associated with the development of Post-ERCP pancreatitis

Post-ERCP pancreatitis (PEP) is an acute pancreatitis caused by endoscopic-retrograde-cholangiopancreatography (ERCP). About 10% of patients develop PEP after ERCP. Here we show that gamma-glutamyltransferase 1 (GGT1)-SNP rs5751901 is an eQTL in pancreatic cells associated with PEP and a positive regulator of the IL-6 amplifier. More PEP patients had the GGT1 SNP rs5751901 risk allele (C) than that of non-PEP patients at Hokkaido University Hospital. Additionally, GGT1 expression and IL-6 amplifier activation were increased in PEP pancreas samples with the risk allele. A mechanistic analysis showed that IL-6-mediated STAT3 nuclear translocation and STAT3 phosphorylation were suppressed in GGT1-deficient cells. Furthermore, GGT1 directly associated with gp130, the signal-transducer of IL-6. Importantly, GGT1-deficiency suppressed inflammation development in a STAT3/NF-κB-dependent disease model. Thus, the risk allele of GGT1-SNP rs5751901 is involved in the pathogenesis of PEP via IL-6 amplifier activation. Therefore, the GGT1-STAT3 axis in pancreas may be a prognosis marker and therapeutic target for PEP.

Reg4 deficiency aggravates pancreatitis by increasing mitochondrial cell death and fibrosis

Regenerating gene family member 4 (Reg4) has been implicated in acute pancreatitis, but its precise functions and involved mechanisms have remained unclear. Herein, we sought to investigate the contribution of Reg4 to the pathogenesis of pancreatitis and evaluate its therapeutic effects in experimental pancreatitis. In acute pancreatitis, Reg4 deletion increases inflammatory infiltrates and mitochondrial cell death and decreases autophagy recovery, which are rescued by the administration of recombinant Reg4 (rReg4) protein. In chronic pancreatitis, Reg4 deficiency aggravates inflammation and fibrosis and inhibits compensatory cell proliferation. Moreover, C-X-C motif ligand 12 (CXCL12)/C-X-C motif receptor 4 (CXCR4) axis is sustained and activated in Reg4-deficient pancreas. The detrimental effects of Reg4 deletion are attenuated by the administration of the approved CXCR4 antagonist plerixafor (AMD3100). Mechanistically, Reg4 mediates its function in pancreatitis potentially via binding its receptor exostosin-like glycosyltransferase 3 (Extl3). In conclusion, our findings suggest that Reg4 exerts a therapeutic effect during pancreatitis by limiting inflammation and fibrosis and improving cellular regeneration.

Improving the prognosis of pancreatic cancer: insights from epidemiology, genomic alterations, and therapeutic challenges

Pancreatic cancer, notorious for its late diagnosis and aggressive progression, poses a substantial challenge owing to scarce treatment alternatives. This review endeavors to furnish a holistic insight into pancreatic cancer, encompassing its epidemiology, genomic characterization, risk factors, diagnosis, therapeutic strategies, and treatment resistance mechanisms. We delve into identifying risk factors, including genetic predisposition and environmental exposures, and explore recent research advancements in precursor lesions and molecular subtypes of pancreatic cancer. Additionally, we highlight the development and application of multi-omics approaches in pancreatic cancer research and discuss the latest combinations of pancreatic cancer biomarkers and their efficacy. We also dissect the primary mechanisms underlying treatment resistance in this malignancy, illustrating the latest therapeutic options and advancements in the field. Conclusively, we accentuate the urgent demand for more extensive research to enhance the prognosis for pancreatic cancer patients.

Characterization of novel PNLIP variants in congenital pancreatic lipase deficiency

BACKGROUND/OBJECTIVES

Studies of a rare homozygous missense mutation identified in two brothers diagnosed with congenital pancreatic lipase deficiency (CPLD) provided the first definitive evidence linking CPLD with missense mutations in the gene of PNLIP. Herein, we investigated the molecular basis for the loss-of-function in the three novel PNLIP variants (c.305G > A, p.(W102∗); c.562C > T, p.(R188C); and c.1257G > A, p.(W419∗)) associated with CPLD.

METHODS

We characterized three novel PNLIP variants in transfected cells by assessing their secretion, intracellular distribution, and markers of endoplasmic reticulum (ER) stress.

RESULTS

All three variants had secretion defects. Notably, the p.R188C and p.W419∗ variants induced misfolding of PNLIP and accumulated as detergent-insoluble aggregates resulting in elevated BiP at both protein and mRNA levels indicating increased ER stress.

CONCLUSIONS

All three novel PNLIP variants cause a loss-of-function through impaired secretion. Additionally, the p.R188C and p.W419∗ variants may induce proteotoxicity through misfolding and potentially increase the risk for pancreatic acinar cell injury.

Identification of protease-sensitive but not misfolding PNLIP variants in familial and hereditary pancreatitis

Mutations in the PNLIP gene have recently been implicated in chronic pancreatitis. Several PNLIP missense variants have been reported to cause protein misfolding and endoplasmic reticulum stress although genetic evidence supporting their association with chronic pancreatitis is currently lacking. Protease-sensitive PNLIP missense variants have also been associated with early-onset chronic pancreatitis although the underlying pathological mechanism remains enigmatic. Herein, we provide new evidence to support the association of protease-sensitive PNLIP variants (but not misfolding PNLIP variants) with pancreatitis. Specifically, we identified protease-sensitive PNLIP variants in 5 of 373 probands (1.3%) with a positive family history of pancreatitis. The protease-sensitive variants, p.F300L and p.I265R, were found to segregate with the disease in three families, including one exhibiting a classical autosomal dominant inheritance pattern. Consistent with previous findings, protease-sensitive variant-positive patients were often characterized by early-onset disease and invariably experienced recurrent acute pancreatitis, although none has so far developed chronic pancreatitis.

Novel Insights Into Immunohistochemical Analysis For Acinar Cell Neoplasm of The Pancreas: Carboxypeptidase A2, Carboxypeptidase A1, and Glycoprotein 2

Acinar cell carcinoma (ACC) is a rare and highly malignant pancreatic tumor. Owing to histologic similarity, ACC is often difficult to distinguish from other solid medullary pancreatic tumors, particularly neuroendocrine neoplasm (NEN) and intraductal tubulopapillary neoplasm (ITPN). We aimed to identify new immunohistochemical markers commonly expressed in tumor cells with acinar cell differentiation and useful for both surgical and small biopsy specimens. Candidate molecules exclusively expressed in neoplastic or non-neoplastic acinar cells in pancreatic tissues with specific and available antibodies suitable for immunohistochemistry were selected. We selected carboxypeptidase A1 (CPA1), carboxypeptidase A2 (CPA2), and glycoprotein 2 (GP2), which were expressed in 100%, 100%, and 96% of cases, respectively, in ACC (n=27) or neoplasia with acinar cell differentiation, including mixed acinar-neuroendocrine carcinoma (n=9), mixed acinar-ductal carcinoma (n=3), pancreatoblastoma (n=4), and acinar cystic transformation (n=2), in the cytoplasm of tumor cells with a granular pattern. Both CPA2 and CPA1 were not expressed in any other tumors without acinar cell differentiation, including NEN (n=44), pancreatic ductal adenocarcinoma (n=44), and ITPN (n=4). GP2 was not expressed in these tumors except in rare cases, including 14% of NEN, 15% of intraductal papillary-mucinous neoplasm, 25% of intraductal oncocytic papillary neoplasm, 25% of ITPN, and 7% of pancreatic ductal adenocarcinoma, wherein a small proportion of tumor cells expressed GP2 in their apical cell membrane. NEN cases also showed cytoplasmic GP2 expression. Therefore, CPA2, CPA1, and potentially GP2 may act as ACC markers.

Preclinical mouse model of a misfolded PNLIP variant develops chronic pancreatitis

OBJECTIVE

Increasing evidence implicates mutation-induced protein misfolding and endoplasm reticulum (ER) stress in the pathophysiology of chronic pancreatitis (CP). The paucity of animal models harbouring genetic risk variants has hampered our understanding of how misfolded proteins trigger CP. We previously showed that pancreatic triglyceride lipase (PNLIP) p.T221M, a variant associated with steatorrhoea and possibly CP in humans, misfolds and elicits ER stress in vitro suggesting proteotoxicity as a potential disease mechanism. Our objective was to create a mouse model to determine if PNLIP p.T221M causes CP and to define the mechanism.

DESIGN

We created a mouse model of Pnlip p.T221M and characterised the structural and biochemical changes in the pancreas aged 1-12 months. We used multiple methods including histochemistry, immunostaining, transmission electron microscopy, biochemical assays, immunoblotting and qPCR.

RESULTS

We demonstrated the hallmarks of human CP in Pnlip p.T221M homozygous mice including progressive pancreatic atrophy, acinar cell loss, fibrosis, fatty change, immune cell infiltration and reduced exocrine function. Heterozygotes also developed CP although at a slower rate. Immunoblot showed that pancreatic PNLIP T221M misfolded as insoluble aggregates. The level of aggregates in homozygotes declined with age and was much lower in heterozygotes at all ages. The Pnlip p.T221M pancreas had increased ER stress evidenced by dilated ER, increased Hspa5 (BiP) mRNA abundance and a maladaptive unfolded protein response leading to upregulation of Ddit3 (CHOP), nuclear factor-κB and cell death.

CONCLUSION

Expression of PNLIP p.T221M in a preclinical mouse model results in CP caused by ER stress and proteotoxicity of misfolded mutant PNLIP.

Novel p.G250A Mutation Associated with Chronic Pancreatitis Highlights Misfolding-Prone Region in Carboxypeptidase A1 (CPA1)

Inborn mutations in the digestive protease carboxypeptidase A1 (CPA1) gene may be associated with hereditary and idiopathic chronic pancreatitis (CP). Pathogenic mutations, such as p.N256K, cause intracellular retention and reduced secretion of CPA1, accompanied by endoplasmic reticulum (ER) stress, suggesting that mutation-induced misfolding underlies the phenotype. Here, we report the novel p.G250A CPA1 mutation found in a young patient with CP. Functional properties of the p.G250A mutation were identical to those of the p.N256K mutation, confirming its pathogenic nature. We noted that both mutations are in a catalytically important loop of CPA1 that is stabilized by the Cys248-Cys271 disulfide bond. Mutation of either or both Cys residues to Ala resulted in misfolding, as judged by the loss of CPA1 secretion and intracellular retention. We re-analyzed seven previously reported CPA1 mutations that affect this loop and found that all exhibited reduced secretion and caused ER stress of varying degrees. The magnitude of ER stress was proportional to the secretion defect. Replacing the naturally occurring mutations with Ala (e.g., p.V251A for p.V251M) restored secretion, with the notable exception of p.N256A. We conclude that the disulfide-stabilized loop of CPA1 is prone to mutation-induced misfolding, in most cases due to the disruptive nature of the newly introduced side chain. We propose that disease-causing CPA1 mutations exhibit abolished or markedly reduced secretion with pronounced ER stress, whereas CPA1 mutations with milder misfolding phenotypes may be associated with lower disease risk or may not be pathogenic at all.

A rare PRSS1 p.S127C mutation is associated with chronic pancreatitis and causes misfolding-induced ER-stress

BACKGROUND

/Objectives: Sequence variants in several genes have been identified as being associated with an increased inherited risk to develop chronic pancreatitis (CP). In a genetic survey of a CP patient we identified in the PRSS1gene a new c.380C > G sequence variation, giving rise to a non-synonymous p.S127C mutation. Functional studies were performed to analyze the associated pathophysiology of the variant.

METHODS

Following generation of an expression vector for the new PRSS1 variant we compared its expression, secretion and catalytic activity with already known PRSS1 risk variants in HEK 293T cells. The intracellular protein accumulation and induction of endoplasmic reticulum (ER)-stress was analyzed.

RESULTS

Prediction tool analysis indicated a probably deleterious effect of the p.S127C variant on protein function which was confirmed by detection of a secretion defect in HEK293T cells leading to intracellular protein accumulation. While protein misfolding was associated with reduced trypsin activity, the increased expression of BIP and presence of spliced XBP1 indicated that the p.S127C variant induces ER stress and activates the UPR signaling pathway.

CONCLUSIONS

The disease mechanism of the PRSS1 p.S127C variant involves defective protein secretion and the induction of ER-stress due to accumulation of presumably misfolded trypsinogen within the ER. The new variant should be considered disease-causing with an incomplete penetrance. Our results confirm that in addition to dysregulated trypsin-activity or reduced fluid secretion, ER-stress induction is an important trigger for acinar cell damage and the development of recurrent or chronic pancreatic inflammation.

The genetic risk factor CEL-HYB1 causes proteotoxicity and chronic pancreatitis in mice

BACKGROUND & AIMS

The CEL gene encodes the digestive enzyme carboxyl ester lipase. CEL-HYB1, a hybrid allele of CEL and its adjacent pseudogene CELP, is a genetic variant suggested to increase the risk of chronic pancreatitis (CP). Our aim was to develop a mouse model for CEL-HYB1 that enables studies of pancreatic disease mechanisms.

METHODS

We established a knock-in mouse strain where the variable number of tandem repeat (VNTR) region of the endogenous mouse Cel gene was substituted with the mutated VNTR of the human CEL-HYB1 allele. Heterozygous and homozygous Cel-HYB1 mice and littermate wildtype controls were characterized with respect to pancreatic pathology and function.

RESULTS

We successfully constructed a mouse model with pancreatic expression of a humanized CEL-HYB1 protein. The Cel-HYB1 mice spontaneously developed features of CP including inflammation, acinar atrophy and fatty replacement, and the phenotype became more pronounced as the animals aged. Moreover, Cel-HYB1 mice were normoglycemic at age 6 months, whereas at 12 months they exhibited impaired glucose tolerance. Immunostaining of pancreatic tissue indicated the formation of CEL protein aggregates, and electron microscopy showed dilated endoplasmic reticulum. Upregulation of the stress marker BiP/GRP78 was seen in pancreatic parenchyma obtained both from Cel-HYB1 animals and from a human CEL-HYB1 carrier.

CONCLUSIONS

We have developed a new mouse model for CP that confirms the pathogenicity of the human CEL-HYB1 variant. Our findings place CEL-HYB1 in the group of genes that increase CP risk through protein misfolding-dependent pathways.

Clinical Characteristics of Patients With Chronic Pancreatitis With or Without Prior Acute Pancreatitis Are Different

OBJECTIVE

The aim of the study is to clarify the clinical characteristics of patients with chronic pancreatitis (CP) who had no prior acute pancreatitis (AP) attack.

METHODS

We retrospectively analyzed patients with CP who were admitted to our center between January 2012 and January 2020.

RESULTS

A total of 274 patients were divided into the following 3 groups: group A: CP without prior AP (n = 103 [37.6%]), group B: CP preceded by a single episode of AP (n = 39 [14.23%]), and group C: CP preceded by recurrent AP (n = 132 [48.18%]). At the diagnosis, patients in group A had a higher incidence of pancreatic duct stones (41.7% vs 25.8%, P = 0.012), higher proportion of idiopathic CP (68.9% vs 48.5%, P = 0.001), and higher mean pancreatic volume change rate (37.61% vs 10.48%, P = 0.007) compared with Group C. Patients in group A underwent the most episodes of extracorporeal shockwave lithotripsy therapy among the 3 groups (P < 0.001).

CONCLUSIONS

Approximately 37.6% of patients had no prior AP attack before CP diagnosis. Patients with CP without prior AP had higher incidence of pancreatic duct stones and pancreas volume shrank faster.

Misfolding-induced chronic pancreatitis in CPA1 N256K mutant mice is unaffected by global deletion of Ddit3/Chop

Genetic mutations in pancreatic digestive enzymes may cause protein misfolding, endoplasmic reticulum (ER) stress and chronic pancreatitis. The CPA1 N256K mouse model carries the human p.N256K carboxypeptidase A1 (CPA1) mutation, a classic example of a pancreatitis-associated misfolding variant. CPA1 N256K mice develop spontaneous, progressive chronic pancreatitis with moderate acinar atrophy, acinar-to-ductal metaplasia, fibrosis, and macrophage infiltration. Upregulation of the ER-stress associated pro-apoptotic transcription factor Ddit3/Chop mRNA was observed in the pancreas of CPA1 N256K mice suggesting that acinar cell death might be mediated through this mechanism. Here, we crossed the CPA1 N256K strain with mice containing a global deletion of the Ddit3/Chop gene (Ddit3-KO mice) and evaluated the effect of DDIT3/CHOP deficiency on the course of chronic pancreatitis. Surprisingly, CPA1 N256K x Ddit3-KO mice developed chronic pancreatitis with a similar time course and features as the CPA1 N256K parent strain. In contrast, Ddit3-KO mice showed no pancreas pathology. The observations indicate that DDIT3/CHOP plays no significant role in the development of misfolding-induced chronic pancreatitis in CPA1 N256K mice and this transcription factor is not a viable target for therapeutic intervention in this disease.

The CEL-HYB1 Hybrid Allele Promotes Digestive Enzyme Misfolding and Pancreatitis in Mice

BACKGROUND & AIMS

A hybrid allele that originated from homologous recombination between CEL and its pseudogene (CELP), CEL-HYB1 increases the risk of chronic pancreatitis (CP). Although suggested to cause digestive enzyme misfolding, definitive in vivo evidence for this postulate has been lacking.

METHODS

CRISPR-Cas9 was used to generate humanized mice harboring the CEL-HYB1 allele on a C57BL/6J background. Humanized CEL mice and C57BL/6J mice were used as controls. Pancreata were collected and analyzed by histology, immunohistochemistry, immunoblotting, and transcriptomics. Isolated pancreatic acini were cultured in vitro to measure the secretion and aggregation of CEL-HYB1 protein. Mice were given caerulein injections to induce acute pancreatitis (AP) and CP.

RESULTS

Pancreata from mice expressing CEL-HYB1 developed pathological features characteristic of focal pancreatitis that included acinar atrophy and vacuolization, inflammatory infiltrates, and fibrosis in a time-dependent manner. CEL-HYB1 expression in pancreatic acini led to decreased secretion and increased intracellular aggregation and triggered endoplasmic reticulum stress compared with CEL. The autophagy levels of pancreata from mice expressing CEL-HYB1 changed at different developmental stages; some aged CEL-HYB1 mice exhibited an accumulation of large autophagic vesicles and impaired autophagy in acinar cells. Administration of caerulein increased the severity of AP/CP in mice expressing CEL-HYB1 compared with control mice, accompanied by higher levels of endoplasmic reticulum stress.

CONCLUSIONS

Expression of a humanized form of CEL-HYB1 in mice promotes endoplasmic reticulum stress and pancreatitis through a misfolding-dependent pathway. Impaired autophagy appears to be involved in the pancreatic injury in aged CEL-HYB1 mice. These mice have the potential to be used as a model to identify therapeutic targets for CP.

Molecular signaling in pancreatic ductal metaplasia: emerging biomarkers for detection and intervention of early pancreatic cancer

Pancreatic ductal metaplasia (PDM) is the transformation of potentially various types of cells in the pancreas into ductal or ductal-like cells, which eventually replace the existing differentiated somatic cell type(s). PDM is usually triggered by and manifests its ability to adapt to environmental stimuli and genetic insults. The development of PDM to atypical hyperplasia or dysplasia is an important risk factor for pancreatic intraepithelial neoplasia (PanIN) and pancreatic ductal adenocarcinoma (PDA). Recent studies using genetically engineered mouse models, cell lineage tracing, single-cell sequencing and others have unraveled novel cellular and molecular insights in PDM formation and evolution. Those novel findings help better understand the cellular origins and functional significance of PDM and its regulation at cellular and molecular levels. Given that PDM represents the earliest pathological changes in PDA initiation and development, translational studies are beginning to define PDM-associated cell and molecular biomarkers that can be used to screen and detect early PDA and to enable its effective intervention, thereby truly and significantly reducing the dreadful mortality rate of PDA. This review will describe recent advances in the understanding of PDM biology with a focus on its underlying cellular and molecular mechanisms, and in biomarker discovery with clinical implications for the management of pancreatic regeneration and tumorigenesis.

Acute Developmental Toxicity of Panax notoginseng in Zebrafish Larvae

OBJECTIVE

To evaluate toxicity of raw extract of Panax notoginseng (rPN) and decocted extract of PN (dPN) by a toxicological assay using zebrafish larvae, and explore the mechanism by RNA sequencing assay.

METHODS

Zebrafish larvae was used to evaluate acute toxicity of PN in two forms: rPN and dPN. Three doses (0.5, 1.5, and 5.0 µ g/mL) of dPN were used to treat zebrafishes for evaluating the developmental toxicity. Behavior abnormalities, body weight, body length and number of vertebral roots were used as specific phenotypic endpoints. RNA sequencing (RNA-seq) assay was applied to clarify the mechanism of acute toxicity, followed by real time PCR (qPCR) for verification. High performance liquid chromatography analysis was performed to determine the chemoprofile of this herb.

RESULTS

The acute toxicity result showed that rPN exerted higher acute toxicity than dPN in inducing death of larval zebrafishes (P<0.01). After daily oral intake for 21 days, dPN at doses of 0.5, 1.5 and 5.0 µ g/mL decreased the body weight, body length, and vertebral number of larval zebrafishes, indicating developmental toxicity of dPN. No other adverse outcome was observed during the experimental period. RNA-seq data revealed 38 genes differentially expressed in dPN-treated zebrafishes, of which carboxypeptidase A1 (cpa1) and opioid growth factor receptor-like 2 (ogfrl2) were identified as functional genes in regulating body development of zebrafishes. qPCR data showed that dPN significantly down-regulated the mRNA expressions of cpa1 and ogfrl2 (both P<0.01), verifying cpa1 and ogfrl2 as target genes for dPN.

CONCLUSION

This report uncovers the developmental toxicity of dPN, suggesting potential risk of its clinical application in children.

Carboxypeptidase A1 (CPA1) Immunohistochemistry Is Highly Sensitive and Specific for Acinar Cell Carcinoma (ACC) of the Pancreas

Carboxypeptidase A1 (CPA1) is a zinc metalloprotease that is produced in pancreatic acinar cells and plays a role in cleaving C-terminal branched-chain and aromatic amino acids from dietary proteins. This study assessed the utility of immunohistochemical CPA1 staining for diagnosing pancreatic acinar cell carcinoma (ACC). A total of 12,274 tumor samples from 132 different tumor types and subtypes as well as 8 samples each of 76 different normal tissue types were interpretable by immunohistochemistry in a tissue microarray format. CPA1 was strongly expressed in acinar cells of all normal pancreas samples but not in any other normal tissues. CPA1 immunostaining was detected in 100% of 11 pancreatic ACCs and 1 mixed acinar endocrine carcinoma, but absent in 449 pancreatic ductal adenocarcinomas, 75 adenocarcinomas of the ampulla Vateri, and 11,739 other evaluable cancers from 128 different tumor entities. A weak to moderate diffuse staining of epithelial and stromal cells of cancer tissues immediately adjacent to non-neoplastic pancreatic acinar cells often occurred and was considered to be caused by the diffusion of the highly abundant CPA1 from normal acinar cells that may have suffered some autolytic cell damage. In conclusion, our data show that CPA1 is a highly sensitive and largely specific marker for normal and neoplastic pancreatic acinar cells. CPA1 immunohistochemistry greatly facilitates the otherwise often difficult diagnosis of pancreatic ACC.

Genetic Evaluation of Pancreatitis

Hereditary pancreatitis (HP) is a rare inherited chronic pancreatitis (CP) with strong genetic associations, with estimated prevalence ranging from 0.3 to 0.57 per 100,000 across Europe, North America, and East Asia. Apart from the most well-described genetic variants are PRSS1, SPINK1, and CFTR, many other genes, such as CTRC, CPA1, and CLDN2 and CEL have been found to associate with HP, typically in one of the 3 main mechanisms such as altered trypsin activity, pancreatic ductal cell secretion, and calcium channel regulation. The current mainstay of management for patients with HP comprises genetic testing for eligible individuals and families, alcohol and tobacco cessation avoidance, pain control, and judicious screening for complications, including exocrine and endocrine insufficiency and pancreatic cancer.

Endoplasmic stress-inducing variants in CPB1 and CPA1 and risk of pancreatic cancer: A case-control study and meta-analysis

Gene variants that encode pancreatic enzymes with impaired secretion can induce pancreatic acinar endoplasmic reticulum (ER) stress, cellular injury and pancreatitis. The role of such variants in pancreatic cancer risk has received little attention. We compared the prevalence of ER stress-inducing variants in CPA1 and CPB1 in patients with pancreatic ductal adenocarcinoma (PDAC cases), enrolled in the National Familial Pancreas Tumor Registry, to their prevalence in noncancer controls in the Genome Aggregation Database (gnomAD). Variants of unknown significance were expressed and variants with reduced secretion assessed for ER stress induction. In vitro assessments were compared with software predictions of variant function. Protein variant software was used to assess variants found in only one gnomAD control ("n-of-one" variants). A meta-analysis of prior PDAC case/control studies was also performed. Of the 1385 patients with PDAC, 0.65% were found to harbor an ER stress-inducing variant in CPA1 or CPB1, compared to 0.17% of the 64 026 controls (odds ratio [OR]: 3.80 [1.92-7.51], P = .0001). ER stress-inducing variants in the CPA1 gene were identified in 4 of 1385 PDAC cases vs 77 of 64 026 gnomAD controls (OR: 2.4 [0.88-6.58], P = .087), and variants in CPB1 were detected in 5 of 1385 cases vs 33 of 64 026 controls (OR: 7.02 [2.74-18.01], P = .0001). Meta-analysis demonstrated strong associations for pancreatic cancer and ER-stress inducing variants for both CPA1 (OR: 3.65 [1.58-8.39], P < .023) and CPB1 (OR: 9.51 [3.46-26.15], P < .001). Rare variants in CPB1 and CPA1 that induce ER stress are associated with increased odds of developing pancreatic cancer.

Missense PNLIP mutations impeding pancreatic lipase secretion cause protein misfolding and endoplasmic reticulum stress

BACKGROUND/OBJECTIVE

Mutation-induced misfolding of digestive enzymes has been shown to cause chronic pancreatitis. Recently, heterozygous pancreatic lipase (PNLIP) mutations leading to reduced secretion were identified. The aim of the present study was to investigate whether PNLIP mutants with a secretion defect result in endoplasmic reticulum (ER) stress in cell culture models.

METHODS

We introduced the coding DNA for wild-type and A174P, G233E, C254R and V454F mutant PNLIP into two mammalian cell lines and carried out functional assays to assess PNLIP expression, secretion and ER stress.

RESULTS

We found that wild-type PNLIP was readily secreted from the investigated cell lines. In contrast, none of the lipase mutants were detectable in the conditioned media. PNLIP variants accumulated in the cells as intracellular protein aggregates probably due to misfolding in the ER. Consistent with this notion, PNLIP mutants induced ER stress, as indicated by increased mRNA levels of spliced X-box Binding Protein 1 (XBP1) and the ER chaperone Immunoglobulin Binding Protein (BiP).

CONCLUSION

The results indicate that PNLIP mutations associated with a lipase secretion defect cause ER stress and thereby may increase the risk for chronic pancreatitis.

[Pathogenesis of chronic pancreatitis]

Long-term alcohol consumption and gene mutations are the most important causes of chronic pancreatitis. In addition to mutations in acinar genes, such as digestive enzymes and their inhibitors, defects in genes that primarily or exclusively affect the duct cells have also been described in recent years. Genetic changes are found not only in patients with a positive family history (hereditary pancreatitis) but also in so-called idiopathic and, to a lesser extent, in alcoholic chronic pancreatitis. The coming years will likely show that there are very complex interactions between environmental influences and numerous genetic factors.

Factors associated with prior acute pancreatitis episodes among patients with chronic pancreatitis

BACKGROUND

The relationship between chronic pancreatitis (CP) and acute pancreatitis (AP) is complex and not well understood. CP could be preceded by antecedent episodes of AP.

AIMS

The aim of this study was to explore both genetic and environmental factors associated with AP episodes before the diagnosis of CP.

METHODS

This was a cross-sectional study including 1022 patients. Detailed demographic, genetic, and clinical data were collected. Based on the presence of AP episode(s) before diagnosis of CP, patients were divided into AP group (further classified into single episode of AP group and recurrent AP group) and non-AP group. Related factors among these groups were assessed using multivariate logistic regression model.

RESULTS

Before diagnosis of CP, 737 patients (72.1%) had a history of AP. Smoking(P = 0.005) and heavy alcohol consumption(P = 0.002) were risk factors for AP while age at CP onset(P < 0.001), harboring the SPINK1 mutation(P < 0.001), diabetes(P < 0.001) and steatorrhea(P < 0.001) were protective factors. Further, alcoholic CP(P = 0.019) was the only independent risk factor for recurrent AP attacks while age at onset of CP(P < 0.001), pancreatic stones(P = 0.024). and pseudocysts(P = 0.018) served as protective factors.

CONCLUSIONS

SPINK1 mutations served as protective factor for AP episodes, suggesting SPINK1 mutation might play a pathogenic role in CP occurrence with occult clinical manifestations.

Dahuang Danshen Decoction Inhibits Pancreatic Fibrosis by Regulating Oxidative Stress and Endoplasmic Reticulum Stress

Background

In Traditional Chinese Medicine (TCM), Dahuang Danshen decoction (DD) is used to treat pancreatic fibrosis. Pancreatic fibrosis is a typical manifestation of chronic pancreatitis (CP), which affects the digestive system. The therapeutic mechanisms of DD in pancreatic fibrosis are unclear.

Aim

This study aimed to investigate the regulatory mechanisms of DD on oxidative stress and endoplasmic reticulum stress in CP.

Materials and Methods

Experimental rats were intraperitoneally injected with 500 mg/kg BW of diethyldithiocarbamate (DDC) twice a week for six weeks to induce CP. At the same time, DD was administered orally at daily doses of 1.37 g/kg BW, 2.74 g/kg BW, and 5.48 g/kg BW to evaluate its treatment effects on CP. After all treatments, pancreatic tissues were harvested and subjected to H&E staining. Transmission electron microscopy (TEM) was also performed to show the endoplasmic reticulum structure in the pancreatic tissues. Immunohistochemistry was used to detect the α-SMA expression level in the pancreatic tissues. Metabolomics analysis of the serum and proteomics analysis of the pancreatic tissues were performed to reveal the changes of endogenous metabolites and proteins, respectively. Concentrations of GSH, MDA, SOD, ROS, col-1, and col-3 were determined using corresponding kits. The western blotting method was used to determine the protein levels of Keap-1, HO-1, NQO1, Nrf2, GRP, JNK, and caspase 12. The pancreatic mRNA levels of NQO1, GPX1, HO-1, GST-π, GRP, JNK, and caspase 12 were also determined by quantitative PCR. The interactions between TCM components and Keap-1 were investigated by molecular docking modeling.

Results

The pathohistological results demonstrated that DD could ameliorate DDC-induced CP in vivo, indicated by reduction of α-SMA, col-1, col-3, TNF-α, and IL-6. DD increased serum levels of GSH and SOD but reduced pancreatic ROS. DD decreased cytoplasmic Keap-1 and increased Nrf2 nuclear localization. Correspondingly, DD increased the expression levels of Nrf2 downstream antioxidant genes NQO1, GPX1, HO-1, and GST-π. DD also decreased ERS hallmarks caspase 12 cleavage and GRP expression. Eventually, DD inhibited PSC activation by reducing JNK phosphorylation and MMK-3/p38 expression. Molecular docking analysis showed that salvianolic acid B and emodin had a good binding affinity toward Keap-1.

Conclusions

These results demonstrated that DD could ameliorate the oxidative and endoplasmic reticulum stress through releasing Nrf2 from Keap-1 binding and inducing the downstream antioxidant enzymes. As a result, DD could thwart pancreatic fibrosis by inhibiting PSCs activation, which was induced by OS and ERS through JNK and MMK3/p38 pathways.

FOXA3 induction under endoplasmic reticulum stress contributes to non-alcoholic fatty liver disease

BACKGROUND & AIMS

Chronic endoplasmic reticulum (ER) stress in the liver has been shown to play a causative role in non-alcoholic fatty liver disease (NAFLD) progression, yet the underlying molecular mechanisms remain to be elucidated. Forkhead box A3 (FOXA3), a member of the FOX family, plays critical roles in metabolic homeostasis, although its possible functions in ER stress and fatty liver progression are unknown.

METHODS

Adenoviral delivery, siRNA delivery, and genetic knockout mice were used to crease FOXA3 gain- or loss-of-function models. Tunicamycin (TM) and a high-fat diet (HFD) were used to induce acute or chronic ER stress in mice. Chromatin immunoprecipiation (ChIP)-seq, luciferase assay, and adenoviral-mediated downstream gene manipulations were performed to reveal the transcriptional axis involved. Key axis protein levels in livers from healthy donors and patients with NAFLD were assessed via immunohistochemical staining.

RESULTS

FOXA3 transcription is specifically induced by XBP1s upon ER stress. FOXA3 exacerbates the excessive lipid accumulation caused by the acute ER-inducer TM, whereas FOXA3 deficiency in hepatocytes and mice alleviates it. Importantly, FOXA3 deficiency in mice reduced diet-induced chronic ER stress, fatty liver, and insulin resistance. In addition, FOXA3 suppression via siRNA or adeno-associated virus delivery ameliorated the fatty liver phenotype in HFD-fed and db/db mice. Mechanistically, ChIP-Seq analysis revealed that FOXA3 directly regulates Period1 (Per1) transcription, which in turn promotes the expression of lipogenic genes, including Srebp1c, thus enhancing lipid synthesis. Of pathophysiological significance, FOXA3, PER1, and SREBP1c levels were increased in livers of obese mice and patients with NAFLD.

CONCLUSION

The present study identified FOXA3 as the bridging molecule that links ER stress and NAFLD progression. Our results highlighted the role of the XBP1s-FOXA3-PER1/Srebp1c transcriptional axis in the development of NAFLD and identified FOXA3 as a potential therapeutic target for fatty liver disease.

LAY SUMMARY

The molecular mechanisms linking endoplasmic reticulum stress to non-alcoholic fatty liver disease (NAFLD) progression remain undefined. Herein, via in vitro and in vivo analysis, we identified Forkhead box A3 (FOXA3) as a key bridging molecule. Of pathophysiological significance, FOXA3 protein levels were increased in livers of obese mice and patients with NAFLD, indicating that FOXA3 could be a potential therapeutic target in fatty liver disease.

Protein misfolding in combination with other risk factors in CEL-HYB1-mediated chronic pancreatitis

OBJECTIVES

The hybrid allele of the carboxyl ester lipase gene (CEL-HYB1) is a genetic risk factor for chronic pancreatitis (CP) although the mechanism promoting disease development is largely unknown. Here, we aimed to clinically describe subjects carrying the CEL-HYB1 allele and to elucidate why the protein product is pathogenic by analyzing pancreatic secretions and cellular models.

METHODS

Norwegian cases (n = 154) diagnosed with recurrent acute pancreatitis or CP were subjected to genetic screening by a CEL-HYB1-specific PCR assay followed by Sanger sequencing. For investigation of CEL-HYB1 protein secretion, duodenal juice samples from cases and controls were analyzed by western blotting. HEK293cells were transfected with constructs expressing CEL-HYB1 or the normal CEL protein (CEL-WT) and analyzed by qPCR, cell fractionation and western blotting.

RESULTS

Two CEL-HYB1-positive families were identified. In both pedigrees, CEL-HYB1 did not fully co-segregate with disease. One proband had recurrent acute pancreatitis and was an active smoker. Her mother was a CEL-HYB1 carrier who had suffered from several attacks of acute pancreatitis until she stopped smoking. The other proband was diagnosed with CP and pancreas divisum. Her CEL-HYB1-positive parent was symptom-free but exhibited pancreatic imaging changes. When analyzing the CEL protein in duodenal juice, CEL-WT was readily detectable but no band corresponding to the risk variant was seen. In CEL-HYB1-transfected cells, we observed impaired protein secretion, protein aggregation and endoplasmic reticulum stress.

CONCLUSION

Our data suggest that CEL-HYB1, in combination with well-known pancreatitis risk factors, causes disease through the misfolding-dependent pathway of genetic CP risk.

Genetic Risk Factors in Early-Onset Nonalcoholic Chronic Pancreatitis: An Update

Chronic pancreatitis (CP) is a progressive, irreversible inflammatory disorder of the pancreas, which results from interrelations between different genetic and environmental factors. Genetic variants are the primary cause of the disease in early-onset nonalcoholic CP patients. Novel CP-associated genes are continuously emerging from genetic studies on CP cohorts, providing important clues for distinct mechanisms involved in CP development. On the basis of functional studies, the genetic alterations have been sub-grouped into CP-driving pathological pathways. This review focuses on the concept of CP as a complex disease driven by multiple genetic factors. We will discuss only well-defined genetic risk factors and distinct functional pathways involved in CP development, especially in the context of the early-onset nonalcoholic CP group. The diagnostic implications of the genetic testing will be addressed as well.

The position of single-base deletions in the VNTR sequence of the carboxyl ester lipase (CEL) gene determines proteotoxicity

Variable number of tandem repeat (VNTR) sequences in the genome can have functional consequences that contribute to human disease. This is the case for the CEL gene, which is specifically expressed in pancreatic acinar cells and encodes the digestive enzyme carboxyl ester lipase. Rare single-base deletions (DELs) within the first (DEL1) or fourth (DEL4) VNTR segment of CEL cause maturity-onset diabetes of the young, type 8 (MODY8), an inherited disorder characterized by exocrine pancreatic dysfunction and diabetes. Studies on the DEL1 variant have suggested that MODY8 is initiated by CEL protein misfolding and aggregation. However, it is unclear how the position of single-base deletions within the CEL VNTR affects pathogenic properties of the protein. Here, we investigated four naturally occurring CEL variants, arising from single-base deletions in different VNTR segments (DEL1, DEL4, DEL9, and DEL13). When the four variants were expressed in human embryonic kidney 293 cells, only DEL1 and DEL4 led to significantly reduced secretion, increased intracellular aggregation, and increased endoplasmic reticulum stress compared with normal CEL protein. The level of O-glycosylation was affected in all DEL variants. Moreover, all variants had enzymatic activity comparable with that of normal CEL. We conclude that the longest aberrant protein tails, resulting from single-base deletions in the proximal VNTR segments, have highest pathogenic potential, explaining why DEL1 and DEL4 but not DEL9 and DEL13 have been observed in patients with MODY8. These findings further support the view that CEL mutations cause pancreatic disease through protein misfolding and proteotoxicity, leading to endoplasmic reticulum stress and activation of the unfolded protein response.

Scale and Scope of Gene-Alcohol Interactions in Chronic Pancreatitis: A Systematic Review

BACKGROUND

Excessive alcohol consumption has long been known to be the primary cause of chronic pancreatitis (CP) but genetic risk factors have been increasingly identified over the past 25 years. The scale and scope of gene-alcohol interactions in CP nevertheless remain unclear.

METHODS

All studies that had obtained genetic variant data concurrently on alcoholic CP (ACP) patients, non-ACP (NACP) patients and normal controls were collated. Employing normal controls as a common baseline, paired OR_ACP and OR_NACP (odds ratios associated with ACP and NACP, respectively) values were calculated and used to assess gene-alcohol interactions.

RESULTS

Thirteen variants involving PRSS1, SPINK1, CTRC, CLDN2, CPA1, CEL and CTRB1-CTRB2, and varying from very rare to common, were collated. Seven variants had an OR_ACP > OR_NACP, which was regarded as an immediate indicator of gene-alcohol interactions in CP. Variants with an OR_ACP < OR_NACP were also found to interact with alcohol consumption by virtue of their impact on age at first pancreatitis symptoms in ACP.

CONCLUSIONS

This study revealed evidence for extensive gene-alcohol interactions in CP. Our findings lend support to the hypothesis that alcohol affects the expression of genetically determined CP and highlight a predominant role of weak-effect variants in the development of ACP.

Deficient Endoplasmic Reticulum Acetyl-CoA Import in Pancreatic Acinar Cells Leads to Chronic Pancreatitis

BACKGROUND & AIMS

Maintaining endoplasmic reticulum (ER) proteostasis is essential for pancreatic acinar cell function. Under conditions of severe ER stress, activation of pathogenic unfolded protein response pathways plays a central role in the development and progression of pancreatitis. Less is known, however, of the consequence of perturbing ER-associated post-translational protein modifications on pancreatic outcomes. Here, we examined the role of the ER acetyl-CoA transporter AT-1 on pancreatic homeostasis.

METHODS

We used an AT-1S113R/+ hypomorphic mouse model, and generated an inducible, acinar-specific, AT-1 knockout mouse model, and performed histologic and biochemical analyses to probe the effect of AT-1 loss on acinar cell physiology.

RESULTS

We found that AT-1 expression is down-regulated significantly during both acute and chronic pancreatitis. Furthermore, acinar-specific deletion of AT-1 in acinar cells induces chronic ER stress marked by activation of both the spliced x-box binding protein 1 and protein kinase R-like ER kinase pathways, leading to spontaneous mild/moderate chronic pancreatitis evidenced by accumulation of intracellular trypsin, immune cell infiltration, and fibrosis. Induction of acute-on-chronic pancreatitis in the AT-1 model led to acinar cell loss and glad atrophy.

CONCLUSIONS

These results indicate a key role for AT-1 in pancreatic acinar cell homeostasis, the unfolded protein response, and that perturbations in AT-1 function leads to pancreatic disease.

Single nucleotide polymorphisms in CEL-HYB1 increase risk for chronic pancreatitis through proteotoxic misfolding

Genetic variants contribute to the risk of chronic pancreatitis (CP) in adults and children. The risk variant CEL-HYB1, a recombinant hybrid allele of CEL and its neighboring pseudogene (CELP), encodes a pathogenic variant of the pancreatic digestive enzyme carboxyl ester lipase (CEL). We previously identified combinations of two non-synonymous SNPs, c.1463T>C (p. Ile488Thr) and c.1643C>T (p. Thr548Ile), in the break point region of CEL-HYB1. Herein, we tested whether these missense variants alter CP risk and their impact on functional properties of the CEL-HYB1 protein. Examination of CEL-HYB1 haplotypes in European patients and controls revealed that the combinationThr488-Ile548 was present only in cases (p ≤ .001). The lipase activity of purified recombinant CEL-HYB1 variants showed normal or near normal activity. CEL-HYB variants expressed in HEK293T cells all had decreased secretion compared with CEL, formed intracellular protein aggregates, and triggered endoplasmic reticulum stress. Thus, we propose that the presence of missense variants in CEL-HYB increases the pathogenicity of CEL-HYB1 through misfolding and gain-of-function proteotoxicity. Interestingly, Thr488-Ile548 and Thr488-Thr548 were equally pathogenic in the functional assays even though only the Thr488-Ile548 haplotype was significantly enriched in cases. The explanation for the mismatch between genetic and functional data requires further investigation.

New horizons in pancreatic genetics

PURPOSE OF REVIEW

Pancreatitis remains an intractable disease because no causative treatment is yet available. Recent studies have uncovered some of its underlying pathophysiology, a requirement for identifying potential treatment targets. These advancements were achieved by human genetic studies and by introducing genetic mechanisms into experimental pancreatitis models.

RECENT FINDINGS

Cationic trypsin mutations are the most prominent genetic risk factor for pancreatitis. Investigators have now introduced genetically modified trypsin variants into transgenic animals. In this manner they characterized the role of cellular defense mechanisms, for example degradation of active trypsin by chymotrypsin-C, but also found that increased autoactivation or decreased degradation, not only boost disease severity but also drive progression to chonic pancreatitis. Other studies found that harmful trypsin effects are not restricted to acinar cells, that other digestive enzymes, notably pancreatic elastase, can also induce cellular injury and that endoplasmic-reticulum-stress is an important mechanism when mutations induce protein misfolding.

SUMMARY

Identifying genetic subsceptibility factors for a disease never completely uncovers its underlying pathogenesis or potential treatment targets. This requires studying the mechanisms suggested by genetic findings in experimentel disease models. Pancreatitis is a field, in which much progress has now been achieved by adopting this approach.

Ethanol feeding accelerates pancreatitis progression in CPA1 N256K mutant mice

Alcoholic pancreatitis is a multifactorial, progressive, inflammatory disorder of the pancreas. Alcohol initiates pancreatitis and promotes its progression in the context of genetic susceptibility and/or other environmental risk factors such as smoking. Genetic mutations can cause digestive enzyme misfolding, which induces endoplasmic reticulum (ER) stress and elicits pancreatitis. Here, we tested the hypothesis that alcohol synergizes with misfolding in promoting ER stress and thereby accelerates chronic pancreatitis progression. To this end, we fed an ethanol-containing diet to CPA1 N256K mice, which carry the human p.N256K CPA1 mutation and develop spontaneous chronic pancreatitis. Inexplicably, CPA1 N256K mice suffered generalized seizures after 2-3 wk of ethanol feeding, which resulted in high mortality and the early termination of the study. Analysis of CPA1 N256K mice euthanized after 3-3.5 wk of ethanol feeding revealed more severe chronic pancreatitis associated with significantly increased Hspa5 [ER chaperone immunoglobulin heavy chain-binding protein (BiP)] mRNA levels when compared with CPA1 N256K mice on a control liquid diet. In contrast, ethanol feeding of C57BL/6N mice for 4 wk increased Hspa5 levels to a lesser degree and caused no pancreatitis. We conclude that ethanol feeding synergizes with the misfolding CPA1 mutant in promoting ER stress and thereby accelerates progression of chronic pancreatitis in CPA1 N256K mice.NEW & NOTEWORTHY Alcoholic pancreatitis is a multifactorial, progressive, inflammatory disorder of the pancreas. This study demonstrates that alcohol synergizes with digestive enzyme misfolding in promoting endoplasmic reticulum stress and thereby accelerates progression of chronic pancreatitis.

Identification of irisin as a therapeutic agent that inhibits oxidative stress and fibrosis in a murine model of chronic pancreatitis

BACKGROUND

Abnormal activation of pancreatic stellate cells (PSCs) plays a crucial role in the pathogenesis of chronic pancreatitis (CP). Irisin, an exercise-induced hormone, has been shown to mitigate liver fibrosis by inhibiting the activation of hepatic stellate cells. However, the effect of irisin in CP has not been evaluated.

METHODS

This study aimed to determine whether irisin is protective in CP. CP was induced by 6 IP injections of cerulein (50 μg/kg/body weight). HPSCs were treated with 5 ng/ml TGF-β1 as in vitro experiment.

RESULTS

Our results showed that repeated cerulein injection induced severe pancreatic injury and fibrosis in mice and the serum irisin level in cerulein-treated mice decreased as in CP patients. Excessive oxidative and ER stress was also present in the pancreas of cerulein-treated mice. Irisin treatment significantly alleviated pancreatic injury and fibrosis, which was associated with reduced oxidative and ER stress. In cultured PSCs, irisin directly inhibited TGF-β-induced α-SMA and collagen I expression. This effect appears to be mediated through downregulation of kindlin-2 and inhibition of the SMAD2/3 pathway.

CONCLUSIONS

Irisin alleviated pancreatic injury and fibrosis, which was associated with reduced oxidative and ER stress. Thus, irisin may offer therapeutic potential for patients with CP.

Chronic Pancreatitis: Managing a Difficult Disease

Chronic pancreatitis is characterized by progressive, irreversible morphologic and functional changes that are most commonly attributed to environmental insults, particularly when there is a genetic or anatomic predisposition. Heavy alcohol use and cigarette smoking are the most common environmental risk factors, but both may be absent. Antecedent episodes of acute pancreatitis occur in about half of patients. Abdominal pain is the most common symptom and requires a tailored approach depending on the anatomic changes in the pancreas. Other clinical manifestations include diabetes mellitus, exocrine pancreatic insufficiency, metabolic bone disease, pancreatic cancer, and anatomic complications. Current disease management is centered on risk factor reduction and screening for and treating disease complications. There are no current therapies to delay or retard disease progression, but there are ongoing efforts to more fully understand the natural history of chronic pancreatitis and underlying mechanisms of disease. These studies are expected to provide insights that will transform our approach to disease management and provide increased hope to patients.

Hic-5 deficiency protects cerulein-induced chronic pancreatitis via down-regulation of the NF-κB (p65)/IL-6 signalling pathway

Chronic pancreatitis (CP), characterized by pancreatic fibrosis, is a recurrent, progressive and irreversible disease. Activation of the pancreatic stellate cells (PSCs) is considered a core event in pancreatic fibrosis. In this study, we investigated the role of hydrogen peroxide-inducible clone-5 (Hic-5) in CP. Analysis of the human pancreatic tissue samples revealed that Hic-5 was overexpressed in patients with CP and was extremely low in healthy pancreas. Hic-5 was significant up-regulated in the activated primary PSCs independently from transforming growth factor beta stimulation. CP induced by cerulein injection was ameliorated in Hic-5 knockout (KO) mice, as shown by staining of tissue level. Simultaneously, the activation ability of the primary PSCs from Hic-5 KO mice was significantly attenuated. We also found that the Hic-5 up-regulation by cerulein activated the NF-κB (p65)/IL-6 signalling pathway and regulated the downstream extracellular matrix (ECM) genes such as α-SMA and Col1a1. Therefore, we determined whether suppressing NF-κB/p65 alleviated CP by treating mice with the NF-κB/p65 inhibitor triptolide in the cerulein-induced CP model and found that pancreatic fibrosis was alleviated by NF-κB/p65 inhibition. These findings provide evidence for Hic-5 as a therapeutic target that plays a crucial role in regulating PSCs activation and pancreatic fibrosis.

Animal Models: Challenges and Opportunities to Determine Optimal Experimental Models of Pancreatitis and Pancreatic Cancer

At the 2018 PancreasFest meeting, experts participating in basic research met to discuss the plethora of available animal models for studying exocrine pancreatic disease. In particular, the discussion focused on the challenges currently facing the field and potential solutions. That meeting culminated in this review, which describes the advantages and limitations of both common and infrequently used models of exocrine pancreatic disease, namely, pancreatitis and exocrine pancreatic cancer. The objective is to provide a comprehensive description of the available models but also to provide investigators with guidance in the application of these models to investigate both environmental and genetic contributions to exocrine pancreatic disease. The content covers both nongenic and genetically engineered models across multiple species (large and small). Recommendations for choosing the appropriate model as well as how to conduct and present results are provided.

Natural single-nucleotide deletion in chymotrypsinogen C gene increases severity of secretagogue-induced pancreatitis in C57BL/6 mice

Genetic susceptibility to chronic pancreatitis in humans is frequently associated with mutations that increase activation of the digestive protease trypsin. Intrapancreatic trypsin activation is an early event in experimental acute pancreatitis in rodents, suggesting that trypsin is a key driver of pathology. In contrast to trypsin, the pancreatic protease chymotrypsin serves a protective function by mitigating trypsin activation through degradation. In humans, loss-of-function mutations in chymotrypsin C (CTRC) are common risk factors for chronic pancreatitis; however, the pathogenic effect of CTRC deficiency has not been corroborated in animal models yet. Here we report that C57BL/6 mice that are widely used for genetic manipulations do not express functional CTRC due to a single-nucleotide deletion in exon 2 of the Ctrc gene. We restored a functional Ctrc locus in C57BL/6N mice and demonstrated that in the novel Ctrc+ strain the severity of cerulein-induced experimental acute and chronic pancreatitis was significantly ameliorated. Improved disease parameters were associated with reduced intrapancreatic trypsin activation suggesting a causal link between CTRC-mediated trypsinogen degradation and protection against pancreatitis. Taken together with prior human genetic and biochemical studies, the observations provide conclusive evidence for the protective role of CTRC against pancreatitis.