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

A beneficial adaptive role for CHOP in driving cell fate selection during ER stress

Cellular stresses elicit signaling cascades that are capable of either mitigating the inciting dysfunction or initiating cell death. During endoplasmic reticulum (ER) stress, the transcription factor CHOP is widely recognized to promote cell death. However, it is not clear whether CHOP also has a beneficial role during adaptation. Here, we combine a new, versatile, genetically modified Chop allele with single cell analysis and with stresses of physiological intensity, to rigorously examine the contribution of CHOP to cell fate. Paradoxically, we find that CHOP promotes death in some cells, but proliferation-and hence recovery-in others. Strikingly, this function of CHOP confers to cells a stress-specific competitive growth advantage. The dynamics of CHOP expression and UPR activation at the single cell level suggest that CHOP maximizes UPR activation, which in turn favors stress resolution, subsequent UPR deactivation, and proliferation. Taken together, these findings suggest that CHOP's function can be better described as a "stress test" that drives cells into either of two mutually exclusive fates-adaptation or death-during stresses of physiological intensity.

Krüppel-like Factor 5 Plays an Important Role in the Pathogenesis of Chronic Pancreatitis

Chronic pancreatitis results in the formation of pancreatic intraepithelial neoplasia (PanIN) and poses a risk of developing pancreatic cancer. Our previous study demonstrated that Krüppel-like factor 5 (KLF5) is necessary for forming acinar-to-ductal metaplasia (ADM) in acute pancreatitis. Here, we investigated the role of KLF5 in response to chronic injury in the pancreas. Human tissues originating from chronic pancreatitis patients showed increased levels of epithelial KLF5. An inducible genetic model combining the deletion of Klf5 and the activation of KrasG12D mutant expression in pancreatic acinar cells together with chemically induced chronic pancreatitis was used. The chronic injury resulted in increased levels of KLF5 in both control and KrasG12D mutant mice. Furthermore, it led to numerous ADM and PanIN lesions and extensive fibrosis in the KRAS mutant mice. In contrast, pancreata with Klf5 loss (with or without KrasG12D) failed to develop ADM, PanIN, or significant fibrosis. Furthermore, the deletion of Klf5 reduced the expression level of cytokines and fibrotic components such as Il1b, Il6, Tnf, Tgfb1, Timp1, and Mmp9. Notably, using ChIP-PCR, we showed that KLF5 binds directly to the promoters of Il1b, Il6, and Tgfb1 genes. In summary, the inactivation of Klf5 inhibits ADM and PanIN formation and the development of pancreatic fibrosis.

Spectrum of PRSS1, SPINK1, CTRC, CFTR, and CPA1 Gene Variants in Chronic Pancreatitis Patients in Russia

The aim of the study was to define the spectrum of genetic risk factors of chronic pancreatitis (CP) development in patients living in the European part of the Russian Federation.

Materials and Methods

The study group included 105 patients with CP, with the age of the disease onset under 40 years old (the average age of onset was 26.9 years). The control group consisted of 76 persons without clinical signs of pancreatitis. The diagnosis of chronic pancreatitis in patients was made on the basis of clinical manifestations and the results of laboratory and instrumental investigations. Genetic examination of patients was conducted using the next-generation sequencing (NGS) technology and included targeted sequencing of all exons and exon-intron boundaries of the PRSS1, SPINK1, CTRC, CFTR, and CPA1 genes. The genotyping of the rs61734659 locus of the PRSS2 gene was also conducted.

Results

Genetic risk factors of the CP development were found in 61% of patients. Pathogenic and likely-pathogenic variants associated with the risk of CP development were identified in the following genes: CTRC (37.1% of patients), CFTR (18.1%), SPINK1 (8.6%), PRSS1 (8.6%), and CPA1 (6.7%). The frequent gene variants in Russian patients with CP were as follows: CTRC gene - c.180C>T (rs497078), c.760C>T (rs121909293), c.738_761del24 (rs746224507); cumulative odds ratio (OR) for all risk alleles was 1.848 (95% CI: 1.054-3.243); CFTR gene - c.3485G>T (rs1800120), c.1521_1523delCTT (p.Phe508del, rs113993960), and c.650A>G (rs121909046); OR=2.432 (95% CI: 1.066-5.553). In the SPINK1, PRSS1, and CPA1 genes, pathogenic variants were found only in the group of patients with CP. The frequent variants of the SPINK1 gene include c.101A>G (p.Asn34Ser, rs17107315) and c.194+2T>C (rs148954387); of the PRSS1 gene - c.86A>T (p.Asn29Ile, rs111033566); of the CPA1 gene - c.586-30C>T (rs782335525) and c.696+23_696+24delGG. The OR for the CP development for the c.180TT genotype (rs497078) CTRC according to the recessive model (TT vs. CT+CC) was 7.05 (95% CI: 0.86-263, p=0.011). In the CTRC gene, the variant c.493+49G>C (rs6679763) appeared to be benign, the c.493+51C>A (rs10803384) variant was frequently detected among both the diseased and healthy persons and did not demonstrate a protective effect. The protective factor c.571G>A (p.Gly191Arg, rs61734659) of the PRSS2 gene was detected only in the group of healthy individuals and confirmed its protective role. 12.4% of the patients with CP had risk factors in 2 or 3 genes.

Conclusion

Sequencing of the coding regions of the PRSS1, SPINK1, CTRC, CFTR, and CPA1 genes allowed to identify genetic risk factors of the CP development in 61% of cases. Determining the genetic cause of CP helps to predict the disease course, perform preventive measures in the proband's relatives, and facilitate a personalized treatment of the patient in future.

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.

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.