A preclinical model of chronic pancreatitis driven by trypsinogen autoactivation

From Genes to Environment: Elucidating Pancreatic Carcinogenesis Through Genetically Engineered and Risk Factor-Integrated Mouse Models

Pancreatic cancer is characterized by late diagnosis, therapy resistance, and poor prognosis, necessitating the exploration of early carcinogenesis and prevention methods. Preclinical mouse models have evolved from cell line-based to human tumor tissue- or organoid-derived xenografts, now to humanized mouse models and genetically engineered mouse models (GEMMs). GEMMs, primarily driven by oncogenic Kras mutations and tumor suppressor gene alterations, offer a realistic platform for investigating pancreatic cancer initiation, progression, and metastasis. The incorporation of inducible somatic mutations and CRISPR-Cas9 screening methods has expanded their utility. To better recapitulate tumor initiation triggered by inflammatory cues, common pancreatic risk factors are being integrated into model designs. This approach aims to decipher the role of environmental factors as secondary or parallel triggers of tumor initiation alongside oncogenic burdens. Emerging models exploring pancreatitis, obesity, diabetes, and other risk factors offer significant translational potential. This review describes current mouse models for studying pancreatic carcinogenesis, their combination with inflammatory factors, and their utility in evaluating pathogenesis, providing guidance for selecting the most suitable models for pancreatic cancer research.

Strain-specific differences in cerulein-induced acute and recurrent acute murine pancreatitis

Hyperstimulation with the secretagogue cerulein is a commonly used experimental model to study acute, recurrent acute and chronic pancreatitis in mice. Earlier studies showed that inbred mouse strains had different susceptibility to cerulein-induced pancreatitis. Here, we confirm and extend these findings by characterizing the severity of acute and recurrent acute pancreatitis in the C57BL/6N and FVB/N strains. When acute pancreatitis was induced with repeated cerulein injections, FVB/N mice had more severe pancreatic edema, higher plasma amylase levels, increased inflammatory cell infiltration, and more extensive acinar cell necrosis relative to the C57BL/6N strain. Cerulein elicited higher and more sustained trypsin activity in FVB/N mice relative to C57BL/6N animals, which was likely due to the lower expression of the SPINK1 trypsin inhibitor and the trypsinogen-degrading lysosomal protease cathepsin L. In C57BL/6N mice, we previously showed that pancreatitis responses were more severe during a second attack compared with the initial, sentinel episode. In FVB/N mice, we now found that the second episode was associated with lower pancreas edema and plasma amylase but higher inflammatory cell infiltration than the first attack. The observations reinforce the notion that inbred mouse strains exhibit differences in their pathological responses during acute and recurrent acute pancreatitis.

Overexpression of Tn antigen induces chronic pancreatitis in mice

Altered O-glycosylation is a key contributor to various pathophysiological processes. Notably, the expression of the Tn antigen is primarily attributed to dysfunction of the chaperone Cosmc, while the overexpression of polypeptide N-acetylgalactosaminyltransferases (GalNAc-Ts) has also been implicated in numerous diseases. We generated a transgenic mouse model with conditional Cosmc-knockout and simultaneous overexpression of polypeptide N-acetylgalactosaminyltransferase 2 (GalNT2) mediated by the pancreas-specific transcription factor 1a (Ptf1a)-Cre mouse strain to investigate the effect of Tn antigen overexpression on the pancreas in vivo. Histopathological examination of the transgenic pancreas revealed a chronic pancreatitis phenotype with interlobular fibrosis and focal necrosis after only a few weeks as a result of Tn antigen overexpression. In the later stages, there was a progressive loss of pancreatic parenchyma with consecutive exocrine pancreatic insufficiency and malnutrition in the transgenic mice. Flow cytometric analyses have also confirmed that significant infiltration of immune cells occurs in the course of pancreatitis. In the transgenic mouse model presented here, we demonstrated that overexpression of the Tn antigen in the pancreas results in chronic pancreatitis, highlighting the pathophysiological importance of truncated O-glycosylation.

Biochemical analyses of cystatin-C dimers and cathepsin-B reveals a trypsin-driven feedback mechanism in acute pancreatitis

Acute pancreatitis (AP) is characterised by self-digestion of the pancreas by its own proteases. This pathophysiological initiating event in AP occurs inside pancreatic acinar cells where intrapancreatic trypsinogen becomes prematurely activated by cathepsin B (CTSB), and induces the digestive protease cascade, while cathepsin L (CTSL) degrades trypsin and trypsinogen and therefore prevents the development of AP. These proteases are located in the secretory compartment of acinar cells together with cystatin C (CST3), an endogenous inhibitor of CTSB and CTSL. The results are based on detailed biochemical analysis, site-directed mutagenesis and molecular dynamics simulations in combination with an experimental disease model of AP using CST3 deficient mice. This identifies that CST3 is a critical regulator of CTSB and CTSL activity during AP. CST3 deficient mice show a higher intracellular CTSB activity resulting in elevated trypsinogen activation accompanied by an increased disease severity. This reveals that CST3 can be cleaved by trypsin disabling the inhibition of CTSB, but not of CTSL. Furthermore, dimerised CST3 enhances the CTSB activity by binding to an allosteric pocket specific to the CTSB structure. CST3 shifts from an inhibitor to an activator of CTSB and therefore fuels the intrapancreatic protease cascade during the onset of AP.

Deletion of the WD40 domain of ATG16L1 exacerbates acute pancreatitis, abolishes LAP-like non-canonical autophagy and slows trypsin degradation

The WD40 domain (WDD) of ATG16L1 plays a pivotal role in non-canonical autophagy. This study examined the role of recently identified LAP-like non-canonical autophagy (LNCA) in acute pancreatitis. LNCA involves rapid single-membrane LC3 conjugation to endocytic vacuoles in pancreatic acinar cells. The rationale for this study was the previously observed presence of trypsin in the organelles undergoing LNCA; aberrant trypsin formation is an important factor in pancreatitis development. Here we report that the deletion of WDD (attained in ATG16L1[E230] mice) eliminated LNCA, aggravated caerulein-induced acute pancreatitis and suppressed the fast trypsin degradation observed in both a rapid caerulein-induced disease model and in caerulein-treated isolated pancreatic acinar cells. These experiments indicate that LNCA is a WDD-dependent mechanism and suggest that it plays not an activating but a protective role in acute pancreatitis. Furthermore, palmitoleic acid, another inducer of experimental acute pancreatitis, strongly inhibited LNCA, suggesting a novel mechanism of pancreatic lipotoxicity.Abbreviation: AMY: amylase; AP: acute pancreatitis; CASM: conjugation of Atg8 to single membranes; CCK: cholecystokinin; FAEE model: fatty acid and ethanol model; IL6: interleukin 6; LA: linoleic acid; LAP: LC3-associated phagocytosis; LMPO: lung myeloperoxidase; LNCA: LAP-like non-canonical autophagy; MAP1LC3/LC3: microtubule-associated protein 1 light chain 3; MPO: myeloperoxidase; PMPO: pancreatic myeloperoxidase; POA: palmitoleic acid; WDD: WD40 domain; WT: wild type.

Trypsin in pancreatitis: The culprit, a mediator, or epiphenomenon?

Pancreatitis is a common, life-threatening inflammatory disease of the exocrine pancreas. Its pathogenesis remains obscure, and no specific or effective treatment is available. Gallstones and alcohol excess are major etiologies of pancreatitis; in a small portion of patients the disease is hereditary. Pancreatitis is believed to be initiated by injured acinar cells (the main exocrine pancreas cell type), leading to parenchymal necrosis and local and systemic inflammation. The primary function of these cells is to produce, store, and secrete a variety of enzymes that break down all categories of nutrients. Most digestive enzymes, including all proteases, are secreted by acinar cells as inactive proforms (zymogens) and in physiological conditions are only activated when reaching the intestine. The generation of trypsin from inactive trypsinogen in the intestine plays a critical role in physiological activation of other zymogens. It was proposed that pancreatitis results from proteolytic autodigestion of the gland, mediated by premature/inappropriate trypsinogen activation within acinar cells. The intra-acinar trypsinogen activation is observed in experimental models of acute and chronic pancreatitis, and in human disease. On the basis of these observations, it has been considered the central pathogenic mechanism of pancreatitis - a concept with a century-old history. This review summarizes the data on trypsinogen activation in experimental and genetic rodent models of pancreatitis, particularly the more recent genetically engineered mouse models that mimic mutations associated with hereditary pancreatitis; analyzes the mechanisms mediating trypsinogen activation and protecting the pancreas against its' damaging effects; discusses the gaps in our knowledge, potential therapeutic approaches, and directions for future research. We conclude that trypsin is not the culprit in the disease pathogenesis but, at most, a mediator of some pancreatitis responses. Therefore, the search for effective therapies should focus on approaches to prevent or normalize other intra-acinar pathologic processes, such as defective autophagy leading to parenchymal cell death and unrelenting inflammation.

Examination of duodenal and colonic microbiome changes in mouse models of acute and chronic pancreatitis

The exocrine pancreas is the main source of digestive enzymes which are released from secretory vesicles of acinar cells into the small intestine. Enzymes, including amylases, proteases and lipases, degrade the ingested food and thus determine the nutritional substrate for the gut microbiota. Acute (AP) and chronic pancreatitis (CP) are associated with a transitional or progressive exocrine pancreatic dysfunction, we analysed in the present study how an experimental induction of pancreatitis in mouse models affects the colonic and duodenal microbiome composition. Evaluation by 16 S rRNA gene sequencing revealed specific microbiome changes in colonic as well as in duodenal samples in different models of AP and CP. Mild acute pancreatitis, which is associated with a transient impairment of pancreatic secretion showed only minor changes in microbial composition, comparable to the ones seen in progressive dysfunctional mouse models of CP. The strongest changes were observed in a mouse model of severe AP, which suggest a direct effect of the immune response on gut microbiome in addition to a pancreatic dysfunction. Our data indicate that highly dysbiotic microbiome changes during pancreatitis are more associated with the inflammatory reaction than with a disturbed pancreatic secretion.

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.

Heterozygous Spink1 Deficiency Promotes Trypsin-dependent Chronic Pancreatitis in Mice

BACKGROUND & AIMS

Heterozygous SPINK1 mutations are strong risk factors for chronic pancreatitis in humans, yet heterozygous disruption of mouse Spink1 yielded no pancreatic phenotype. To resolve this contradiction, we used CRISPR/Cas9-mediated genome editing to generate heterozygous Spink1-deleted mice (Spink1-KOhet) in the C57BL/6N strain and studied the effect of this allele in trypsin-independent and trypsin-dependent pancreatitis models.

METHODS

We investigated severity of acute pancreatitis and progression to chronic pancreatitis in Spink1-KOhet mice after transient (10 injections) and prolonged (2 × 8 injections) cerulein hyperstimulation. We crossed Spink1-KOhet mice with T7D23A and T7D22N,K24R mice that carry strongly autoactivating trypsinogen mutants and exhibit spontaneous chronic pancreatitis.

RESULTS

Prolonged but not transient cerulein stimulation resulted in increased intrapancreatic trypsin activity and more severe acute pancreatitis in Spink1-KOhet mice relative to the C57BL/6N control strain. After the acute episode, Spink1-KOhet mice developed progressive disease with chronic pancreatitis-like features, whereas C57BL/6N mice recovered rapidly. Trypsinogen mutant mice carrying the Spink1-KOhet allele exhibited strikingly more severe chronic pancreatitis than the respective parent strains.

CONCLUSIONS

Heterozygous Spink1 deficiency caused more severe acute pancreatitis after prolonged cerulein stimulation and promoted chronic pancreatitis after the cerulein-induced acute episode, and in two strains of trypsinogen mutant mice with spontaneous disease. In contrast, acute pancreatitis induced with limited cerulein hyperstimulation was unaffected by heterozygous Spink1 deletion, in agreement with recent observations that trypsin activity does not mediate pathologic responses in this model. Taken together, the findings strongly support the notion that loss-of-function SPINK1 mutations in humans increase chronic pancreatitis risk in a trypsin-dependent manner.

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.

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.

Intrapancreatic fat, pancreatitis, and pancreatic cancer

Pancreatic cancer is typically detected at an advanced stage, and is refractory to most forms of treatment, contributing to poor survival outcomes. The incidence of pancreatic cancer is gradually increasing, linked to an aging population and increasing rates of obesity and pancreatitis, which are risk factors for this cancer. Sources of risk include adipokine signaling from fat cells throughout the body, elevated levels of intrapancreatic intrapancreatic adipocytes (IPAs), inflammatory signals arising from pancreas-infiltrating immune cells and a fibrotic environment induced by recurring cycles of pancreatic obstruction and acinar cell lysis. Once cancers become established, reorganization of pancreatic tissue typically excludes IPAs from the tumor microenvironment, which instead consists of cancer cells embedded in a specialized microenvironment derived from cancer-associated fibroblasts (CAFs). While cancer cell interactions with CAFs and immune cells have been the topic of much investigation, mechanistic studies of the source and function of IPAs in the pre-cancerous niche are much less developed. Intriguingly, an extensive review of studies addressing the accumulation and activity of IPAs in the pancreas reveals that unexpectedly diverse group of factors cause replacement of acinar tissue with IPAs, particularly in the mouse models that are essential tools for research into pancreatic cancer. Genes implicated in regulation of IPA accumulation include KRAS, MYC, TGF-β, periostin, HNF1, and regulators of ductal ciliation and ER stress, among others. These findings emphasize the importance of studying pancreas-damaging factors in the pre-cancerous environment, and have significant implications for the interpretation of data from mouse models for pancreatic cancer.

Inhibition of mouse trypsin isoforms by SPINK1 and effect of human pancreatitis-associated mutations

Serine protease inhibitor Kazal type 1 (SPINK1) is a trypsin-selective inhibitor protein secreted by the exocrine pancreas. Loss-of-function SPINK1 mutations predispose to chronic pancreatitis through either reduced expression, secretion, or impaired trypsin inhibition. In this study, we aimed to characterize the inhibitory activity of mouse SPINK1 against cationic (T7) and anionic (T8, T9, T20) mouse trypsin isoforms. Kinetic measurements with a peptide substrate, and digestion experiments with β-casein indicated that the catalytic activity of all mouse trypsins is comparable. Human SPINK1 and its mouse ortholog inhibited mouse trypsins with comparable efficiency (K_D range 0.7-2.2 pM), with the sole exception of T7 trypsin, which was inhibited less effectively by the human inhibitor (K_D 21.9 pM). Characterization of four chronic pancreatitis-associated human SPINK1 mutations in the context of the mouse inhibitor revealed that the reactive-loop mutations R42N (human K41N) and I43M (human I42M) impaired SPINK1 binding to trypsin (K_D 60 nM and 47.5 pM, respectively), whereas mutations D35S (human N34S) and A56S (human P55S) had no impact on trypsin inhibition. Our results confirmed that high-affinity trypsin inhibition by SPINK1 is conserved in the mouse, and the functional consequences of human pancreatitis-associated SPINK1 mutations can be replicated in the mouse inhibitor.

Integrated Physiology of the Exocrine and Endocrine Compartments in Pancreatic Diseases: Workshop Proceedings

The Integrated Physiology of the Exocrine and Endocrine Compartments in Pancreatic Diseases workshop was a 1.5-day scientific conference at the National Institutes of Health (Bethesda, MD) that engaged clinical and basic science investigators interested in diseases of the pancreas. This report provides a summary of the proceedings from the workshop. The goals of the workshop were to forge connections and identify gaps in knowledge that could guide future research directions. Presentations were segregated into six major theme areas, including 1) pancreas anatomy and physiology, 2) diabetes in the setting of exocrine disease, 3) metabolic influences on the exocrine pancreas, 4) genetic drivers of pancreatic diseases, 5) tools for integrated pancreatic analysis, and 6) implications of exocrine-endocrine cross talk. For each theme, multiple presentations were followed by panel discussions on specific topics relevant to each area of research; these are summarized here. Significantly, the discussions resulted in the identification of research gaps and opportunities for the field to address. In general, it was concluded that as a pancreas research community, we must more thoughtfully integrate our current knowledge of normal physiology as well as the disease mechanisms that underlie endocrine and exocrine disorders so that there is a better understanding of the interplay between these compartments.

Mouse model of PRSS1 p.R122H-related hereditary pancreatitis highlights context-dependent effect of autolysis-site mutation

Mutation p.R122H in human cationic trypsinogen (PRSS1) is the most frequently identified cause of hereditary pancreatitis. The mutation blocks protective degradation of trypsinogen by chymotrypsin C (CTRC), which involves an obligatory trypsin-mediated cleavage at Arg122. Previously, we found that C57BL/6N mice are naturally deficient in CTRC, and trypsinogen degradation is catalyzed by chymotrypsin B1 (CTRB1). Here, we used biochemical experiments to demonstrate that the cognate p.R123H mutation in mouse cationic trypsinogen (isoform T7) only partially prevented CTRB1-mediated degradation. We generated a novel C57BL/6N mouse strain harboring the p.R123H mutation in the native T7 trypsinogen locus. T7R123H mice developed no spontaneous pancreatitis, and severity parameters of cerulein-induced pancreatitis trended only slightly higher than those of C57BL/6N mice. However, when treated with cerulein for 2 days, more edema and higher trypsin activity was seen in the pancreas of T7R123H mice compared to C57BL/6N controls. Furthermore, about 40% of T7R123H mice progressed to atrophic pancreatitis in 3 days, whereas C57BL/6N animals showed full histological recovery. Taken together, the observations indicate that mutation p.R123H inefficiently blocks chymotrypsin-mediated degradation of mouse cationic trypsinogen, and modestly increases cerulein-induced intrapancreatic trypsin activity and pancreatitis severity. The findings support the notion that the pathogenic effect of the PRSS1 p.R122H mutation in hereditary pancreatitis is dependent on its ability to defuse chymotrypsin-dependent defenses.

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.

Preclinical testing of dabigatran in trypsin-dependent pancreatitis

Pancreatitis, the inflammatory disorder of the pancreas, has no specific therapy. Genetic, biochemical, and animal model studies revealed that trypsin plays a central role in the onset and progression of pancreatitis. Here, we performed biochemical and preclinical mouse experiments to offer proof of concept that orally administered dabigatran etexilate can inhibit pancreatic trypsins and shows therapeutic efficacy in trypsin-dependent pancreatitis. We found that dabigatran competitively inhibited all human and mouse trypsin isoforms (Ki range 10-79 nM) and dabigatran plasma concentrations in mice given oral dabigatran etexilate well exceeded the Ki of trypsin inhibition. In the T7K24R trypsinogen mutant mouse model, a single oral gavage of dabigatran etexilate was effective against cerulein-induced progressive pancreatitis, with a high degree of histological normalization. In contrast, spontaneous pancreatitis in T7D23A mice, which carry a more aggressive trypsinogen mutation, was not ameliorated by dabigatran etexilate, given either as daily gavages or by mixing it with solid chow. Taken together, our observations showed that benzamidine derivatives such as dabigatran are potent trypsin inhibitors and show therapeutic activity against trypsin-dependent pancreatitis in T7K24R mice. Lack of efficacy in T7D23A mice is probably related to the more severe pathology and insufficient drug concentrations in the pancreas.

Between early and established chronic pancreatitis: A proposal of "acinar-ductal hybrid mechanism"

BACKGROUND/OBJECTIVES

The recently proposed "new mechanistic definition of chronic pancreatitis (CP)" categorized early CP as a reversible condition. However, there is no clear explanation regarding the pathological condition of early CP, the reason for the development of the disease in only a small portion of the patients with risk factors, and the mechanism for transition from a reversible pathological condition to an irreversible one.

METHODS

Based on the available information, a mechanism that could provide answers to the queries associated with CP was proposed.

RESULTS

Acinar-ductal coordination is very important for the physiological secretion of pancreatic juice. Inflammation originating from acinar cells undermines the function of proximal ducts and leads to a vicious cycle of sustained inflammation by increasing the viscosity and decreasing the alkalinity of pancreatic juice. Persistent elevation of ductal pressure due to stagnation of pancreatic juice caused by protein plugs, stones, or fibrous scar of ducts converts the reversible pathological condition of early CP to an irreversible one. Diagnostic criteria for early CP proposed by Japanese researchers have enabled to the recognition of patients showing a progression from early to established CP. However, most patients diagnosed with early CP do not experience progression of the disease, suggesting the inadequate specificity of the criteria.

CONCLUSION

The "acinar-ductal hybrid mechanism" may explain the pathological condition and progression of early CP. To diagnose early CP more accurately, it is essential to discover specific biomarkers that can discriminate "early CP" from "acute pancreatitis (AP)/recurrent acute pancreatitis (RAP)" and "established CP." Therapeutic intervention in clinical practices through various new approaches is expected to improve the prognosis of patients with CP.

Double deficiency of cathepsin B and L in the mouse pancreas alters trypsin activity without affecting acute pancreatitis severity

BACKGROUND

Premature intracellular trypsinogen activation has long been considered a key initiator of acute pancreatitis (AP). Cathepsin B (CTSB) activates trypsinogen, while cathepsin L (CTSL) inactivates trypsin(ogen), and both proteins play a role in the onset of AP.

METHODS

AP was induced by 7 hourly intraperitoneal injections of cerulein (50 μg/kg) in wild-type and pancreas-specific conditional Ctsb knockout (Ctsb^Δpan), Ctsl knockout (Ctsl^Δpan), and Ctsb;Ctsl double-knockout (Ctsb^Δpan;Ctsl^Δpan) mice. Pancreatic samples were collected and analyzed by histology, immunohistochemistry, real-time PCR, and immunoblots. Trypsin activity was measured in pancreatic homogenates. Peripheral blood was collected, and serum amylase activity was measured.

RESULTS

Double deletion of Ctsb and Cstl did not affect pancreatic development or mouse growth. After 7 times cerulein injections, double Ctsb and Ctsl deficiency in mouse pancreases increased trypsin activity to the same extent as that in Ctsl-deficient mice, while Ctsb deficiency decreased trypsin activity but did not affect the severity of AP. Ctsb^Δpan;Ctsl^Δpan mice had comparable serum amylase activity and histopathological changes and displayed similar levels of proinflammatory cytokines, apoptosis, and autophagy activity compared with wild-type, Ctsb^Δpan, and Ctsl^Δpan mice.

CONCLUSION

Double deletion of Ctsb and Ctsl in the mouse pancreas altered intrapancreatic trypsin activity but did not affect disease severity and inflammatory response after cerulein-induced AP.

Autophagy, Acute Pancreatitis and the Metamorphoses of a Trypsinogen-Activating Organelle

Recent studies have highlighted the importance of autophagy and particularly non-canonical autophagy in the development and progression of acute pancreatitis (a frequent disease with considerable morbidity and significant mortality). An important early event in the development of acute pancreatitis is the intrapancreatic activation of trypsinogen, (i.e., formation of trypsin) leading to the autodigestion of the organ. Another prominent phenomenon associated with the initiation of this disease is vacuolisation and specifically the formation of giant endocytic vacuoles in pancreatic acinar cells. These organelles develop in acinar cells exposed to several inducers of acute pancreatitis (including taurolithocholic acid and high concentrations of secretagogues cholecystokinin and acetylcholine). Notably, early trypsinogen activation occurs in the endocytic vacuoles. These trypsinogen-activating organelles undergo activation, long-distance trafficking, and non-canonical autophagy. In this review, we will discuss the role of autophagy in acute pancreatitis and particularly focus on the recently discovered LAP-like non-canonical autophagy (LNCA) of endocytic vacuoles.

The Rabep1-Mediated Endocytosis and Activation of Trypsinogen to Promote Pancreatic Stellate Cell Activation

Background: The pathogenesis of chronic pancreatitis is still unclear. Trypsinogen activation is an active factor in acute pancreatitis that has not been studied in the occurrence of chronic pancreatitis. Methods: Immunofluorescence was used to detect the location and expression of trypsinogen in chronic pancreatitis and normal tissues. Microarray and single-cell RNA-seq (scRNA-seq) were used to screen core genes and pathways in pancreatic stellate cells (PSCs). Western blotting and immunofluorescence were used to verify trypsinogen expression in PSCs after silencing Rabep1. Immunofluorescence and flow cytometry were used to validate trypsinogen activation and PSC activation after intervening in the endocytosis pathway. Results: Endocytosed trypsinogen was found in PSCs in CP clinical samples. Bioinformatic analysis showed that Rabep1 is a core gene that regulates trypsinogen endocytosis through the endocytosis pathway, verified by Western blot and immunofluorescence. Immunofluorescence and flow cytometry analyses confirmed the activation of trypsinogen and PSCs through the endocytosis pathway in PSCs. Conclusion: This study discovered a new mechanism by which trypsinogen affects the activation of PSCs and the occurrence and development of CP. Through communication between pancreatic acinar cells and PSCs, trypsinogen can be endocytosed by PSCs and activated by the Rabep1 gene.

Understanding Necroptosis in Pancreatic Diseases

Intermediate between apoptosis and necrosis, necroptosis is a regulated caspase-independent programmed cell death that induces an inflammatory response and mediates cancer development. As our understanding improves, its role in the physiopathology of numerous diseases, including pancreatic diseases, has been reconsidered, and especially in pancreatitis and pancreatic cancer. However, the exact pathogenesis remains elusive, even though some studies have been conducted on these diseases. Its unique mechanisms of action in diseases are expected to bring prospects for the treatment of pancreatic diseases. Therefore, it is imperative to further explore its molecular mechanism in pancreatic diseases in order to identify novel therapeutic options. This article introduces recent related research on necroptosis and pancreatic diseases, explores necroptosis-related molecular pathways, and provides a theoretical foundation for new therapeutic targets for pancreatic diseases.

Specific Temporal Requirement of Prox1 Activity During Pancreatic Acinar Cell Development

BACKGROUND AND AIMS

An interactive regulatory network assembled through the induction and downregulation of distinct transcription factors governs acinar cell maturation. Understanding how this network is built is relevant for protocols of directed pancreatic acinar differentiation. The murine transcription factor Prox1 is highly expressed in multipotent pancreatic progenitors and in various mature pancreatic cell types except for acinar cells. In this study, we investigated when is Prox1 expression terminated in developing acinar cells and the potential involvement of its activity in acinar cell specification/differentiation. We also investigated the effects of sustained Prox1 expression in acinar maturation and maintenance.

METHODS

Prox1 acinar expression was analyzed by immunofluorescence and confocal microscopy. Prox1-null embryos (Prox1GFPCre/Δ), Prox1AcOE transgenic mice, histologic and immunostaining methods, transmission electron microscopy, functional assays, and quantitative RNA and RNA-sequencing methods were used to investigate the effects of Prox1 functional deficiency and sustained Prox1 expression in acinar maturation and homeostasis.

RESULTS

Immunostaining results reveal transient Prox1 expression in newly committed embryonic acinar cells. RNA-sequencing demonstrate precocious expression of multiple "late" acinar genes in the pancreas of Prox1GFPCre/Δ embryos. Prox1AcOE transgenic mice carrying sustained Prox1 acinar expression have relatively normal pancreas development. In contrast, Prox1AcOE adult mice have severe pancreatic alterations involving reduced acinar gene expression, abnormal acinar secretory granules, acinar atrophy, increased endoplasmic reticulum stress, and mild chronic inflammation.

CONCLUSION

Prox1 transient expression in early acinar cells is necessary for correct sequential gene expression. Prox1 expression is terminated in developing acinar cells to complete maturation and to preserve homeostasis.

Hereditary Pancreatitis-25 Years of an Evolving Paradigm: Frank Brooks Memorial Lecture 2021

ABSTRACT

The identification of the genetic basis of hereditary pancreatitis in 1996 confirmed the critical role of trypsinogen in this disease and opened a new avenue of research on pancreatitis-associated genetic risk factors and their mechanism of action. Through the following 25 years, the ensuing discoveries fundamentally changed our understanding of pancreatitis pathogenesis, clarified the role of trypsinogen autoactivation in disease onset and progression, and set the stage for future therapeutic interventions. This Frank Brooks Memorial Lecture was delivered on November 4, 2021, at the 52nd Annual Meeting of the American Pancreatic Association, held in Miami Beach, Florida.

Chronic progression of cerulein-induced acute pancreatitis in trypsinogen mutant mice

T7K24R mice carry mutation p.K24R in mouse cationic trypsinogen (isoform T7), which is analogous to the human hereditary pancreatitis-associated mutation p.K23R. The mutation renders trypsinogen more prone to autoactivation. We recently reported that T7K24R mice exhibit increased severity of acute pancreatitis induced by repeated cerulein injections. The objective of the present study was to test whether trypsinogen mutant mice are prone to develop chronic pancreatitis, as observed in patients. We characterized the natural course of cerulein-induced pancreatitis in T7K24R mice and the C57BL/6N parent strain from the acute episode to 3 months post-attack. As expected, an acute episode of pancreatitis in C57BL/6N mice was followed by rapid recovery and histological restitution. In stark contrast, T7K24R mice developed progressive chronic pancreatitis with acinar cell atrophy, persistent macrophage infiltration, and diffuse fibrosis. The nadir of pancreas damage occurred on days 5-6 after the acute episode and was accompanied by digestive dysfunction. Remarkably, histological recovery was markedly delayed and permanent, chronic changes were still detectable 1-3 months after the acute pancreatitis episode. We conclude that during cerulein-induced acute pancreatitis in T7K24R mice, trypsin triggers an autonomous inflammatory program resulting in chronic disease progression, even after the cessation of cerulein-mediated injury. We propose that this uniquely trypsin-dependent mechanism explains the development of hereditary chronic pancreatitis in humans. Trypsin inhibition during acute attacks should prevent or delay progression to chronic disease.

Trypsinogen (PRSS1 and PRSS2) gene dosage correlates with pancreatitis risk across genetic and transgenic studies: a systematic review and re-analysis

Trypsinogen (PRSS1, PRSS2) copy number gains and regulatory variants have both been proposed to elevate pancreatitis risk through a gene dosage effect (i.e., by increasing the expression of wild-type protein). However, to date, their impact on pancreatitis risk has not been thoroughly evaluated whilst the underlying pathogenic mechanisms remain to be explicitly investigated in mouse models. Genetic studies of the rare trypsinogen duplication and triplication copy number variants (CNVs), and the common rs10273639C variant, were collated from PubMed and/or ClinVar. Mouse studies that analyzed the influence of a transgenically expressed wild-type human PRSS1 or PRSS2 gene on the development of pancreatitis were identified from PubMed. The genetic effects of the different risk genotypes, in terms of odds ratios, were calculated wherever appropriate. The genetic effects of the rare trypsinogen duplication and triplication CNVs were also evaluated by reference to their associated disease subtypes. We demonstrate a positive correlation between increased trypsinogen gene dosage and pancreatitis risk in the context of the rare duplication and triplication CNVs, and between the level of trypsinogen expression and disease risk in the context of the heterozygous and homozygous rs10273639C-tagged genotypes. We retrospectively identify three mouse transgenic studies that are informative in relation to the pathogenic mechanism underlying the trypsinogen gene dosage effect in pancreatitis. Trypsinogen gene dosage correlates with pancreatitis risk across genetic and transgenic studies, highlighting the fundamental role of dysregulated expression of wild-type trypsinogen in the etiology of pancreatitis. Specifically downregulating trypsinogen expression in the pancreas may serve as a potential therapeutic and/or prevention strategy for pancreatitis.

Evolutionary expansion of polyaspartate motif in the activation peptide of mouse cationic trypsinogen limits autoactivation and protects against pancreatitis

The activation peptide of mammalian trypsinogens typically contains a tetra-aspartate motif (positions P2-P5 in Schechter-Berger numbering) that inhibits autoactivation and facilitates activation by enteropeptidase. This evolutionary mechanism protects the pancreas from premature trypsinogen activation while allowing physiological activation in the gut lumen. Inborn mutations that disrupt the tetra-aspartate motif cause hereditary pancreatitis in humans. A subset of trypsinogen paralogs, including the mouse cationic trypsinogen (isoform T7), harbor an extended penta-aspartate motif (P2-P6) in their activation peptide. Here, we demonstrate that deletion of the extra P6 aspartate residue (D23del) increased the autoactivation of T7 trypsinogen threefold. Mutagenesis of the P6 position in wild-type T7 trypsinogen revealed that bulky hydrophobic side chains are preferred for maximal autoactivation, and deletion-induced shift of the P7 Leu to P6 explains the autoactivation increase in the D23del mutant. Accordingly, removal of the P6 Leu by NH₂-terminal truncation with chymotrypsin C reduced the autoactivation of the D23del mutant. Homozygous T7D23del mice carrying the D23del mutation did not develop spontaneous pancreatitis and severity of cerulein-induced acute pancreatitis was comparable with that of C57BL/6N controls. However, sustained stimulation with cerulein resulted in markedly increased histological damage in T7D23del mice relative to C57BL/6N mice. Furthermore, when the T7D23del allele was crossed to a chymotrypsin-deficient background, the double-mutant mice developed spontaneous pancreatitis at an early age. Taken together, the observations argue that evolutionary expansion of the polyaspartate motif in mouse cationic trypsinogen contributes to the natural defenses against pancreatitis and validate the role of the P6 position in autoactivation control of mammalian trypsinogens.NEW & NOTEWORTHY Unwanted autoactivation of the digestive protease trypsinogen can result in pancreatitis. The trypsinogen activation peptide contains a polyaspartate motif that suppresses autoactivation. This study demonstrates that evolutionary expansion of these aspartate residues in mouse cationic trypsinogen further inhibits autoactivation and enhances protection against pancreatitis.

Trypsin-Mediated Sensitization to Ferroptosis Increases the Severity of Pancreatitis in Mice

BACKGROUND & AIMS

Pancreatitis is characterized by acinar cell death and persistent inflammation. Ferroptosis is a type of lipid peroxidation-dependent necrosis, which is negatively regulated by glutathione peroxidase 4. We studied how trypsin, a serine protease secreted by pancreatic acinar cells, affects the contribution of ferroptosis to triggering pancreatitis.

METHODS

In vitro, the mouse pancreatic acinar cell line 266-6 and mouse primary pancreatic acinar cells were used to investigate the effect of exogenous trypsin on ferroptosis sensitivity. Short hairpin RNAs were designed to silence gene expression, whereas a library of 1080 approved drugs was used to identify new ferroptosis inhibitors in 266-6 cells. In vivo, a Cre/LoxP system was used to generate mice with a pancreas-specific knockout of Gpx4 (Pdx1-Cre;Gpx4^flox/flox mice). Acute or chronic pancreatitis was induced in these mice (Gpx4^flox/flox mice served as controls) by cerulein injections or a Lieber-DeCarli alcoholic liquid diet. Pancreatic tissues, acinar cells, and serum were collected and analyzed by histology, immunoblot, quantitative polymerase chain reaction, enzyme-linked immunosorbent assay, or immunohistochemical analyses.

RESULTS

Supraphysiological doses of trypsin (500 or 1000 ng/mL) alone did not trigger significant cell death in 266-6 cells and mouse primary pancreatic acinar cells, but did increase the sensitivity of these cells to ferroptosis upon treatment with cerulein, L-arginine, alcohol, erastin, or RSL3. Proteasome 26S subunit, non-adenosine triphosphatase 4-dependent lipid peroxidation caused ferroptosis in pancreatic acinar cells by promoting the proteasomal degradation of glutathione peroxidase 4. The drug screening campaign identified the antipsychotic drug olanzapine as an antioxidant inhibiting ferroptosis in pancreatic acinar cells. Mice lacking pancreatic Gpx4 developed more severe pancreatitis after cerulein infection or ethanol feeding than control mice. Conversely, olanzapine administration protected against pancreatic ferroptotic damage and experimental pancreatitis in Gpx4-deficient mice.

CONCLUSIONS

Trypsin-mediated sensitization to ferroptotic damage increases the severity of pancreatitis in mice, and this process can be reversed by olanzapine.

[Pathogenesis of acute pancreatitis]

Acute pancreatitis is characterized by the autodigestion of the pancreas by its own digestive enzymes. The pathophysiological onset of the disease occurs in the acinar cells. The normally inactive precursors of secreted proteases are prematurely activated and as a result digest the cells from within. The activation of trypsinogen to trypsin represents the key event as active trypsin activates further digestive enzymes and can therefore initiate the activation of the complete protease cascade. This premature activation of proteases results in the cell death of acinar cells and in the induction of a strong proinflammatory immune response. Cells of the innate immune system migrate into the damaged organ and potentiate the local damage again via the release of inflammatory cytokines, such as tumor necrosis factor alpha and reactive oxygen species. Concomitant to the local immune reaction, a systemic activation of the immune system also occurs, which can develop into a systemic inflammatory response syndrome (SIRS). In the course of the SIRS severe complications such as organ failure can occur. The consequence of this pronounced SIRS in the later course of the disease is a strong immunological counter-regulation, the so-called compensatory anti-inflammatory reaction syndrome (CARS). In the course of this immunosuppression commensal bacteria from the intestines can colonize the pancreatic necrosis. The outcome of the SIRS/CARS balance is decisive for the course and the prognosis of the patient.

Mouse model suggests limited role for human mesotrypsin in pancreatitis

Mesotrypsin is a low-abundance human trypsin isoform with a unique evolutionary mutation that conferred resistance to trypsin inhibitors and restricted substrate specificity. Mesotrypsin degrades the serine protease inhibitor Kazal type 1 (SPINK1) and thereby might increase risk for pancreatitis. Here, we report a mouse model designed to test the role of mesotrypsin in pancreatitis. We introduced the human mesotrypsin evolutionary signature mutation into mouse cationic trypsinogen (isoform T7), resulting in a Gly to Arg change at the corresponding position 199. In biochemical experiments using purified proteins, the p.G199R T7 mutant recapitulated all salient features of human mesotrypsin. T7G199R mice developed normally with no spontaneous pancreatitis or other obvious phenotypic changes. Cerulein-induced acute pancreatitis in C57BL/6N and T7G199R mice showed similar severity with respect to inflammatory parameters and acinar cell necrosis while plasma amylase activity was higher in T7G199R mice. Neither SPINK1 degradation nor elevated intrapancreatic trypsin activation was apparent in T7G199R mice. The results indicate that in T7G199R mice the newly created mesotrypsin-like activity has no significant impact on cerulein-induced pancreatitis. The observations suggest that human mesotrypsin is unimportant for pancreatitis; a notion that is consistent with published human genetic studies.

Diversity and Biology of Cancer-Associated Fibroblasts

Efforts to develop anti-cancer therapies have largely focused on targeting the epithelial compartment, despite the presence of non-neoplastic stromal components that substantially contribute to the progression of the tumor. Indeed, cancer cell survival, growth, migration, and even dormancy are influenced by the surrounding tumor microenvironment (TME). Within the TME, cancer-associated fibroblasts (CAFs) have been shown to play several roles in the development of a tumor. They secrete growth factors, inflammatory ligands, and extracellular matrix proteins that promote cancer cell proliferation, therapy resistance, and immune exclusion. However, recent work indicates that CAFs may also restrain tumor progression in some circumstances. In this review, we summarize the body of work on CAFs, with a particular focus on the most recent discoveries about fibroblast heterogeneity, plasticity, and functions. We also highlight the commonalities of fibroblasts present across different cancer types, and in normal and inflammatory states. Finally, we present the latest advances regarding therapeutic strategies targeting CAFs that are undergoing preclinical and clinical evaluation.

Experimental Acute Pancreatitis Models: History, Current Status, and Role in Translational Research

Acute pancreatitis is a potentially severe inflammatory disease that may be associated with a substantial morbidity and mortality. Currently there is no specific treatment for the disease, which indicates an ongoing demand for research into its pathogenesis and development of new therapeutic strategies. Due to the unpredictable course of acute pancreatitis and relatively concealed anatomical site in the retro-peritoneum, research on the human pancreas remains challenging. As a result, for over the last 100 years studies on the pathogenesis of this disease have heavily relied on animal models. This review aims to summarize different animal models of acute pancreatitis from the past to present and discuss their main characteristics and applications. It identifies key studies that have enhanced our current understanding of the pathogenesis of acute pancreatitis and highlights the instrumental role of animal models in translational research for developing novel therapies.

Pancreatic Fibroblast Heterogeneity: From Development to Cancer

Pancreatic ductal adenocarcinoma (PDA) is characterized by an extensive fibroinflammatory microenvironment that accumulates from the onset of disease progression. Cancer-associated fibroblasts (CAFs) are a prominent cellular component of the stroma, but their role during carcinogenesis remains controversial, with both tumor-supporting and tumor-restraining functions reported in different studies. One explanation for these contradictory findings is the heterogeneous nature of the fibroblast populations, and the different roles each subset might play in carcinogenesis. Here, we review the current literature on the origin and function of pancreatic fibroblasts, from the developing organ to the healthy adult pancreas, and throughout the initiation and progression of PDA. We also discuss clinical approaches to targeting fibroblasts in PDA.

P-selectin glycoprotein ligand 1 deficiency prevents development of acute pancreatitis by attenuating leukocyte infiltration

BACKGROUND

Acute pancreatitis (AP) is rapid-onset pancreatic inflammation that causes local and systemic inflammatory response syndrome (SIRS) with high morbidity and mortality, but no approved therapies are currently available. P-selectin glycoprotein ligand 1 (PSGL-1) is a transmembrane glycoprotein to initiate inflammatory responses. We hypothesized that PSGL-1 may be involved in the development of AP and would be a new target for the treatment of AP.

AIM

To investigate the role and mechanism of PSGL-1 in the development of AP.

METHODS

The PSGL-1 expression on leukocytes was detected in peripheral blood of AP patients and volunteers. Pancreatic injury, inflammatory cytokines expression, and inflammatory cell infiltration was measured in AP mouse models induced with PSGL-1 knockout (PSGL-1^-/-) and wild-type (PSGL-1^+/+) mice. Leukocyte-endothelial cell adhesion was measured in a peripheral blood mononuclear cell (PBMC)-endothelial cell coculture system.

RESULTS

The expression of PSGL-1 on monocytes and neutrophils was significantly increased in AP patients. Compared with PSGL-1^+/+ mice, PSGL-1^-/- AP mice induced by caerulein exhibited lower serum amylase, less Interleukin-1beta (IL-1beta) and Interleukin-6 (IL-6) expression, less neutrophil and macrophage infiltration, and reduced peripheral neutrophil and monocyte accounts. PSGL-1 deficiency alleviated leukocyte-endothelial cell adhesion via IL-6 but not IL-1beta.

CONCLUSION

PSGL-1 deficiency effectively inhibits the development of AP by preventing leukocyte-endothelial cell adhesion via IL-6 stimulation and may become a potential therapeutic target for treating AP.

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.

Lumenal Galectin-9-Lamp2 interaction regulates lysosome and autophagy to prevent pathogenesis in the intestine and pancreas

Intracellular galectins are carbohydrate-binding proteins capable of sensing and repairing damaged lysosomes. As in the physiological conditions glycosylated moieties are mostly in the lysosomal lumen but not cytosol, it is unclear whether galectins reside in lysosomes, bind to glycosylated proteins, and regulate lysosome functions. Here, we show in gut epithelial cells, galectin-9 is enriched in lysosomes and predominantly binds to lysosome-associated membrane protein 2 (Lamp2) in a Asn(N)-glycan dependent manner. At the steady state, galectin-9 binding to glycosylated Asn175 of Lamp2 is essential for functionality of lysosomes and autophagy. Loss of N-glycan-binding capability of galectin-9 causes its complete depletion from lysosomes and defective autophagy, leading to increased endoplasmic reticulum (ER) stress preferentially in autophagy-active Paneth cells and acinar cells. Unresolved ER stress consequently causes cell degeneration or apoptosis that associates with colitis and pancreatic disorders in mice. Therefore, lysosomal galectins maintain homeostatic function of lysosomes to prevent organ pathogenesis.

Loss of chymotrypsin-like protease (CTRL) alters intrapancreatic protease activation but not pancreatitis severity in mice

The digestive enzyme chymotrypsin protects the pancreas against pancreatitis by reducing harmful trypsin activity. Genetic deficiency in chymotrypsin increases pancreatitis risk in humans and pancreatitis severity in mice. Pancreatic chymotrypsin is produced in multiple isoforms including chymotrypsin B1, B2, C and chymotrypsin-like protease (CTRL). Here we investigated the role of CTRL in cerulein-induced pancreatitis in mice. Biochemical experiments with recombinant mouse enzymes demonstrated that CTRL cleaved trypsinogens and suppressed trypsin activation. We generated a novel CTRL-deficient strain (Ctrl-KO) using CRISPR-Cas9 genome engineering. Homozygous Ctrl-KO mice expressed no detectable CTRL protein in the pancreas. Remarkably, the total chymotrypsinogen content in Ctrl-KO mice was barely reduced indicating that CTRL is a low-abundance isoform. When given cerulein, Ctrl-KO mice exhibited lower intrapancreatic chymotrypsin activation and a trend for higher trypsin activation, compared with C57BL/6N mice. Despite the altered protease activation, severity of cerulein-induced acute pancreatitis was similar in Ctrl-KO and C57BL/6N mice. We conclude that CTRL is a minor chymotrypsin isoform that plays no significant role in cerulein-induced pancreatitis in mice.

Preclinical insights into the gut-skeletal muscle axis in chronic gastrointestinal diseases

Muscle wasting represents a constant pathological feature of common chronic gastrointestinal diseases, including liver cirrhosis (LC), inflammatory bowel diseases (IBD), chronic pancreatitis (CP) and pancreatic cancer (PC), and is associated with increased morbidity and mortality. Recent clinical and experimental studies point to the existence of a gut‐skeletal muscle axis that is constituted by specific gut‐derived mediators which activate pro‐ and anti‐sarcopenic signalling pathways in skeletal muscle cells. A pathophysiological link between both organs is also provided by low‐grade systemic inflammation. Animal models of LC, IBD, CP and PC represent an important resource for mechanistic and preclinical studies on disease‐associated muscle wasting. They are also required to test and validate specific anti‐sarcopenic therapies prior to clinical application. In this article, we review frequently used rodent models of muscle wasting in the context of chronic gastrointestinal diseases, survey their specific advantages and limitations and discuss possibilities for further research activities in the field. We conclude that animal models of LC‐, IBD‐ and PC‐associated sarcopenia are an essential supplement to clinical studies because they may provide additional mechanistic insights and help to identify molecular targets for therapeutic interventions in humans.

Early trypsin activation develops independently of autophagy in caerulein-induced pancreatitis in mice

Premature intrapancreatic trypsinogen activation is widely regarded as an initiating event for acute pancreatitis. Previous studies have alternatively implicated secretory vesicles, endosomes, lysosomes, or autophagosomes/autophagolysosomes as the primary site of trypsinogen activation, from which a cell-damaging proteolytic cascade originates. To identify the subcellular compartment of initial trypsinogen activation we performed a time-resolution analysis of the first 12 h of caerulein-induced pancreatitis in transgenic light chain 3 (LC3)-GFP autophagy reporter mice. Intrapancreatic trypsin activity increased within 60 min and serum amylase within 2 h, but fluorescent autophagosome formation only by 4 h of pancreatitis in parallel with a shift from cytosolic LC3-I to membranous LC3-II on Western blots. At 60 min, activated trypsin in heavier subcellular fractions was co-distributed with cathepsin B, but not with the autophagy markers LC3 or autophagy protein 16 (ATG16). Supramaximal caerulein stimulation of primary pancreatic acini derived from LC3-GFP mice revealed that trypsinogen activation is independent of autophagolysosome formation already during the first 15 min of exposure to caerulein. Co-localization studies (with GFP-LC3 autophagosomes versus Ile-Pro-Arg-AMC trypsin activity and immunogold-labelling of lysosomal-associated membrane protein 2 [LAMP-2] versus trypsinogen activation peptide [TAP]) indicated active trypsin in autophagolysosomes only at the later timepoints. In conclusion, during the initiating phase of caerulein-induced pancreatitis, premature protease activation develops independently of autophagolysosome formation and in vesicles arising from the secretory pathway. However, autophagy is likely to regulate overall intracellular trypsin activity during the later stages of this disease.

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.

Mutation That Promotes Activation of Trypsinogen Increases Severity of Secretagogue-Induced Pancreatitis in Mice

BACKGROUND & AIMS

Mutations in the human serine protease 1 gene (PRSS1), which encodes cationic trypsinogen, can accelerate its autoactivation and cause hereditary or sporadic chronic pancreatitis. Disruption of the locus that encodes cationic trypsinogen in mice (T7) causes loss of expression of the protein, but only partially decreases the severity of secretagogue-induced acute pancreatitis and has no effect on chronic pancreatitis. We investigated whether trypsinogen becomes pathogenic only when its activation is promoted by mutation.

METHODS

We generated mice with knock-in of the p.K24R mutation (called T7K24R mice), which is analogous to human PRSS1 mutation p.K23R. We gave T7K24R and C57BL/6N (control) mice repeated injections of cerulein to induce pancreatitis. Plasma amylase activity, pancreatic edema, and myeloperoxidase content in pancreas and lungs were quantified. We expressed mutant and full-length forms of PRSS1 in Escherichia coli and compared their autoactivation.

RESULTS

The p.K24R mutation increased autoactivation of T7 5-fold. T7K24R mice developed no spontaneous pancreatitis. T7K24R mice given cerulein injections had increased pancreatic activation of trypsinogen and more edema, infiltration of lung and pancreas by inflammatory cells, and plasma amylase activity compared with control mice given cerulein injections. Injection of cerulein for 2 days induced progressive pancreatitis in T7K24R mice, but not in control mice, with typical features of chronic pancreatitis.

CONCLUSIONS

Introduction of a mutation into mice that is analogous to the p.K23R mutation in PRSS1 increases pancreatic activation of trypsinogen during secretagogue-induced pancreatitis. Higher pancreatic activity of trypsin increases the severity of pancreatitis, even though loss of trypsin activity does not prevent pancreatitis in mice.

Trypsin activity governs increased susceptibility to pancreatitis in mice expressing human PRSS1R122H

Currently, an effective targeted therapy for pancreatitis is lacking. Hereditary pancreatitis (HP) is a heritable, autosomal-dominant disorder with recurrent acute pancreatitis (AP) progressing to chronic pancreatitis (CP) and a markedly increased risk of pancreatic cancer. In 1996, mutations in PRSS1 were linked to the development of HP. Here, we developed a mouse model by inserting a full-length human PRSS1R122H gene, the most commonly mutated gene in human HP, into mice. Expression of PRSS1R122H protein in the pancreas markedly increased stress signaling pathways and exacerbated AP. After the attack of AP, all PRSS1R122H mice had disease progression to CP, with similar histologic features as those observed in human HP. By comparing PRSS1R122H mice with PRSS1WT mice, as well as enzymatically inactivated Dead-PRSS1R122H mice, we unraveled that increased trypsin activity is the mechanism for R122H mutation to sensitize mice to the development of pancreatitis. We further discovered that trypsin inhibition, in combination with anticoagulation therapy, synergistically prevented progression to CP in PRSS1R122H mice. These animal models help us better understand the complex nature of this disease and provide powerful tools for developing and testing novel therapeutics for human pancreatitis.

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.