Regional differences in the cellular proliferation activity of the regenerating rat pancreas after partial pancreatectomy

Heart Failure and Pancreas Exocrine Insufficiency: Pathophysiological Mechanisms and Clinical Point of View

Heart failure is associated with decreased tissue perfusion and increased venous congestion that may result in organ dysfunction. This dysfunction has been investigated extensively for many organs, but data regarding pancreatic (exocrine) dysfunction are scarce. In the present review we will discuss the available data on the mechanisms of pancreatic damage, how heart failure can lead to exocrine dysfunction, and its clinical consequences. We will show that heart failure causes significant impairment of pancreatic exocrine function, particularly in the elderly, which may exacerbate the clinical syndrome of heart failure. In addition, pancreatic exocrine insufficiency may lead to further deterioration of cardiovascular disease and heart failure, thus constituting a true vicious circle. We aim to provide insight into the pathophysiological mechanisms that constitute this reciprocal relation. Finally, novel treatment options for pancreatic dysfunction in heart failure are discussed.

Clinical significance of pancreatic ductal metaplasia

Pancreatic ductal metaplasia (PDM) is the stepwise replacement of differentiated somatic cells with ductal or ductal-like cells in the pancreas. PDM is usually triggered by cellular and environmental insults. PDM development may involve all cell lineages of the pancreas, and acinar cells with the highest plasticity are the major source of PDM. Pancreatic progenitor cells are also involved as cells of origin or transitional intermediates. PDM is heterogeneous at the histological, cellular, and molecular levels and only certain subsets of PDM develop further into pancreatic intraepithelial neoplasia (PanIN) and then pancreatic ductal adenocarcinoma (PDAC). The formation and evolution of PDM is regulated at the cellular and molecular levels through a complex network of signaling pathways. The key molecular mechanisms that drive PDM formation and its progression into PanIN/PDAC remain unclear, but represent key targets for reversing or inhibiting PDM. Alternatively, PDM could be a source of pancreas regeneration, including both exocrine and endocrine components. Cellular aging and apoptosis are obstacles to PDM-to-PanIN progression or pancreas regeneration. Functional identification of the cellular and molecular events driving senescence and apoptosis in PDM and its progression would help not only to restrict the development of PDM into PanIN/PDAC, but may also facilitate pancreatic regeneration. This review systematically assesses recent advances in the understanding of PDM physiology and pathology, with a focus on its implications for enhancing regeneration and prevention of cancer. © 2022 The Pathological Society of Great Britain and Ireland.

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.

EMT and Stemness-Key Players in Pancreatic Cancer Stem Cells

Metastasis and tumor progression are the major cause of death in patients suffering from pancreatic ductal adenocarcinoma. Tumor growth and especially dissemination are typically associated with activation of an epithelial-to-mesenchymal transition (EMT) program. This phenotypic transition from an epithelial to a mesenchymal state promotes migration and survival both during development and in cancer progression. When re-activated in pathological contexts such as cancer, this type of developmental process confers additional stemness properties to specific subsets of cells. Cancer stem cells (CSCs) are a subpopulation of cancer cells with stem-like features that are responsible for the propagation of the tumor as well as therapy resistance and cancer relapse, but also for circulating tumor cell release and metastasis. In support of this concept, EMT transcription factors generate cells with stem cell properties and mediate chemoresistance. However, their role in pancreatic ductal adenocarcinoma metastasis remains controversial. As such, a better characterization of CSC populations will be crucial in future development of therapies targeting these cells. In this review, we will discuss the latest updates on the mechanisms common to pancreas development and CSC-mediated tumor progression.

Pancreatic β-cell regeneration: Facultative or dedicated progenitors?

The adult pancreas is only capable of limited regeneration. Unlike highly regenerative tissues such as the skin, intestinal crypts and hematopoietic system, no dedicated adult stem cells or stem cell niche have so far been identified within the adult pancreas. New β cells have been shown to form in the adult pancreas, in response to high physiological demand or experimental β-cell ablation, mostly by replication of existing β cells. The possibility that new β cells are formed from other sources is currently a point of major controversy. Under particular injury conditions, fully differentiated pancreatic duct and acinar cells have been shown to dedifferentiate into a progenitor-like state, however the extent, to which ductal, acinar or other endocrine cells contribute to restoring pancreatic β-cell mass remains to be resolved. In this review we focus on regenerative events in the pancreas with emphasis on the restoration of β-cell mass. We present an overview of regenerative responses noted within the different pancreatic lineages, following injury. We also highlight the intrinsic plasticity of the adult pancreas that allows for inter-conversion of fully differentiated pancreatic lineages through manipulation of few genes or growth factors. Taken together, evidence from a number of studies suggest that differentiated pancreatic lineages could act as facultative progenitor cells, but the extent to which these contribute to β-cell regeneration in vivo is still a matter of contention.

Stem cells versus plasticity in liver and pancreas regeneration

Cell replacement in adult organs can be achieved through stem cell differentiation or the replication or transdifferentiation of existing cells. In the adult liver and pancreas, stem cells have been proposed to replace tissue cells, particularly following injury. Here we review how specialized cell types are produced in the adult liver and pancreas. Based on current evidence, we propose that the plasticity of differentiated cells, rather than stem cells, accounts for tissue repair in both organs.

Centroacinar cells: At the center of pancreas regeneration

The process of regeneration serves to heal injury by replacing missing cells. Understanding regeneration can help us replace cell populations lost during disease, such as the insulin-producing β cells lost in diabetic patients. Centroacinar cells (CACs) are a specialized ductal pancreatic cell type that act as progenitors to replace β cells in the zebrafish. However, whether CACs contribute to β-cell regeneration in adult mammals remains controversial. Here we review the current understanding of the role of CACs as endocrine progenitors during regeneration in zebrafish and mammals.

Centroacinar Cells Are Progenitors That Contribute to Endocrine Pancreas Regeneration

Diabetes is associated with a paucity of insulin-producing β-cells. With the goal of finding therapeutic routes to treat diabetes, we aim to find molecular and cellular mechanisms involved in β-cell neogenesis and regeneration. To facilitate discovery of such mechanisms, we use a vertebrate organism where pancreatic cells readily regenerate. The larval zebrafish pancreas contains Notch-responsive progenitors that during development give rise to adult ductal, endocrine, and centroacinar cells (CACs). Adult CACs are also Notch responsive and are morphologically similar to their larval predecessors. To test our hypothesis that adult CACs are also progenitors, we took two complementary approaches: 1) We established the transcriptome for adult CACs. Using gene ontology, transgenic lines, and in situ hybridization, we found that the CAC transcriptome is enriched for progenitor markers. 2) Using lineage tracing, we demonstrated that CACs do form new endocrine cells after β-cell ablation or partial pancreatectomy. We concluded that CACs and their larval predecessors are the same cell type and represent an opportune model to study both β-cell neogenesis and β-cell regeneration. Furthermore, we show that in cftr loss-of-function mutants, there is a deficiency of larval CACs, providing a possible explanation for pancreatic complications associated with cystic fibrosis.

The impact of potential islet precursor cells on islet autotransplantation outcomes

Islet autotransplant patients represent excellent subjects to assess the posttransplant impact of islet precursors, as chronic pancreatitis (CP) causes an elevation of ductal cells, pancreatic precursors cells, and hormone-positive acinar cells. The relationship between these cell types and autograft outcomes should be more apparent than would be the case in the context of an allograft program with confounding immunological variables. To improve diabetic control following total pancreatectomy for CP, nonpurified islets were autotransplanted into the liver. Pancreas specimens were recovered from 23 patients and stained for antigens including: insulin, glucagon, cytokeratin 19, cytokeratin 7, and PDX-1. In line with previous reports, the prevalence of ductal cells, non-islet endocrine cells and non-islet PDX-1-expressing cells was significantly higher in CP glands compared with normal pancreata. When correlating follow-up data (i.e., fasting and stimulated C-peptide/glucose levels and HbA1c%) with pancreas immunoreactivity, high levels of ductal cells, non-islet PDX-1-positive cells, and non-islet glucagon-positive cells were associated with superior outcomes, detectable up to 2 years posttransplant. To conclude, the acinar parenchyma and ductal epithelium of the CP pancreas show an upregulation of both endocrine and pre-endocrine cell types, which appear to have a positive effect on islet graft outcomes in autotransplantation setting.

Exocrine ontogenies: on the development of pancreatic acinar, ductal and centroacinar cells

This review summarizes our current understanding of exocrine pancreas development, including the formation of acinar, ductal and centroacinar cells. We discuss the transcription factors associated with various stages of exocrine differentiation, from multipotent progenitor cells to fully differentiated acinar and ductal cells. Within the branching epithelial tree of the embryonic pancreas, this involves the progressive restriction of multipotent pancreatic progenitor cells to either a central "trunk" domain giving rise to the islet and ductal lineages, or a peripheral "tip" domain giving rise to acinar cells. This review also discusses the soluble morphogens and other signaling pathways that influence these events. Finally, we examine centroacinar cells as an enigmatic pancreatic cell type whose lineage remains uncertain, and whose possible progenitor capacities continue to be explored.

Notch-responsive cells initiate the secondary transition in larval zebrafish pancreas

Zebrafish provide a highly versatile model in which to study vertebrate development. Many recent studies have elucidated early events in the organogenesis of the zebrafish pancreas; however, several aspects of early endocrine pancreas formation in the zebrafish are not homologous to the mammalian system. To better identify mechanisms of islet formation in the zebrafish, with true homology to those observed in mammals, we have temporally and spatially characterized zebrafish secondary islet formation. As is the case in the mouse, we show that Notch inhibition leads to precocious differentiation of endocrine tissues. Furthermore, we have used transgenic fish expressing fluorescent markers under the control of a Notch-responsive element to observe the precursors of these induced endocrine cells. These pancreatic Notch-responsive cells represent a novel population of putative progenitors that are associated with larval pancreatic ductal epithelium, suggesting functional homology between secondary islet formation in zebrafish and the secondary transition in mammals. We also show that Notch-responsive cells persist in the adult pancreas and possess the classical characteristics of centroacinar cells, a cell type believed to be a multipotent progenitor cell in adult mammalian pancreas.

Healthy twin birth after autologous islet transplantation in a pancreatectomized patient due to a benign tumor

OBJECTIVE

Autologous islet transplantation has been reported to show favorable outcomes on glucose metabolism. The objective of this study was to describe successful delivery of twins in an islet recipient who had undergone distal pancreatectomy.

PATIENT

A 35-year-old woman who underwent distal pancreatectomy owing to a solid pseudopapillary neoplasm received an autologous islet transplantation (140,000 islet equivalents). After 2.5 years, she unexpectedly became pregnant. Cesarean section was performed at 35 weeks delivering male twins without complications. Plasma glucose and insulin levels, insulinogenic index, and hemoglobin A1c were measured from the preoperative to the postpartum state as the main outcome.

RESULTS

The patient showed impaired glucose tolerance before pancreatectomy, but improved to a normal glucose tolerance after transplantation, maintaining euglycemia until pregnancy. Because her fasting glucose levels were within the normal range during pregnancy, fasting insulin represented insulin resistance. Her fasting insulin levels abruptly increased in the third trimester of pregnancy, but returned after delivery. Insulinogenic index increased over 1 year after transplantation, but gradually decreased thereafter. During pregnancy, it increased again, but could not compensate for the insulin resistance. Therefore, gestational diabetes mellitus developed: glucose homeostasis recovered to normal after delivery.

CONCLUSIONS

The current report suggested a successful pregnancy after autologous islet transplantation that did not itself permanently deteriorate graft function.

Morphological changes in the rat endocrine pancreas within 12 h of intravenous streptozotocin administration

We examined early morphological changes in pancreatic endocrine cells within 12 h of intravenous streptozotocin (STZ) administration (60 mg/kg). Thirty rats were allocated either to a control group (vehicle alone) or to one of four experimental groups tested after 3, 6, 9 and 12 h. Karyopyknosis and cytoplasmic vacuoles were first observed in beta-cell cytoplasm 3 h after STZ administration (STZ-3 h), and the most severe damage was found in beta cells at STZ-12 h. Insulin-positive non-islet cells were observed near the intercalated duct (ICD) and/or centroacinar (CA) cells at STZ-6 h and their numbers peaked at STZ-6 h. The distribution patterns of the insulin-positive cells and those of nestin and insulin-like growth factor-1 were similar and their nuclei were positive for proliferating cell nuclear antigen. Thus, ICD cells and/or CA cells reacted immediately to transform into insulin-secreting cells to replace injured beta cells (or to compensate for the lack of beta cells) within 12 h of STZ administration.

Transdifferentiation, metaplasia and tissue regeneration

Transdifferentiation is defined as the conversion of one cell type to another. It belongs to a wider class of cell type transformations called metaplasias which also includes cases in which stem cells of one tissue type switch to a completely different stem cell. Numerous examples of transdifferentiation exist within the literature. For example, isolated striated muscle of the invertebrate jellyfish (Anthomedusae) has enormous transdifferentiation potential and even functional organs (e.g., tentacles and the feeding organ (manubrium)) can be generated in vitro. In contrast, the potential for transdifferentiation in vertebrates is much reduced, at least under normal (nonpathological) conditions. But despite these limitations, there are some well-documented cases of transdifferentiation occurring in vertebrates. For example, in the newt, the lens of the eye can be formed from the epithelial cells of the iris. Other examples of transdifferentiation include the appearance of hepatic foci in the pancreas, the development of intestinal tissue at the lower end of the oesophagus and the formation of muscle, chondrocytes and neurons from neural precursor cells. Although controversial, recent results also suggest the ability of adult stem cells from different embryological germlayers to produce differentiated cells e.g., mesodermal stem cells forming ecto- or endodermally-derived cell types. This phenomenon may constitute an example of metaplasia. The current review examines in detail some well-documented examples of transdifferentiation, speculates on the potential molecular and cellular mechanisms that underlie the switches in phenotype, together with their significance to organogenesis and regenerative medicine.

The expression of pancreatic endocrine markers in centroacinar cells of the normal and regenerating rat pancreas: their possible transformation to endocrine cells

To determine the progenitor nature of centroacinar cells (CACs), we attempted to compare the expression pattern of endocrine cell markers and PDX-1 (pancreatic duodenal homeobox gene 1) in CACs of both the quiescent and the regenerating rat pancreas. In the normal pancreas, most CACs were relatively small cells with sparse cytoplasm and oval or elongated nuclei. In addition, we noticed a distinct population of a small number of large cells with round nuclei in the centroacinar region. By immunohistochemistry, 0.21% and 0.3% of CACs in normal rat pancreas were respectively found positive for glucagon and insulin, being large CACs and designated as GL-CAC and IL-CAC. They also exhibited the mRNA of each hormone by in situ hybridization (ISH). The ISH signal for glucagon but not insulin was also detected in a subset of small CACs (designated GS-CAC). The expression of PDX-1 was also observed in subsets of small and large CACs (PS-CAC and PL-CAC, respectively). After a 90% pancreatectomy, the relative frequency for GS-CACs, but not those for other CACs, was significantly reduced in two days after surgery. On day 7 after surgery, the number of GS-CACs recovered to preoperative levels, whereas GL-CACs, IL-CACs, PS-CAC, and PL-CAC gradually increased to about double in number. From these results, a portion of CACs was suggested to differentiated into endocrine cells. A possible cell lineage is discussed for endocrine neogenesis during pancreatic regeneration.

Generating new pancreas from old

Pancreas regeneration after tissue damage is a key response to pancreatic injury, involving pancreatic duct progenitor cells and intra-islet precursor cells. Surgical removal of the pancreas, duct obstruction by cellophane wrapping and bone marrow-derived stem cell transplantation act as inductive stimuli, leading to pancreas regeneration. The exact role of growth and differentiation factors regulating pancreatic beta-cell mass remains unknown. Here, I will attempt to integrate recent findings and speculate on the factors that trigger this fascinating response, wherein the pancreas responds to a deficit in cell mass and undergoes new islet formation, leading to restoration of normal beta-cell mass. I will also discuss recent advances in regenerating endocrine pancreatic cells, which could affect stem cell-based approaches to treating diabetes mellitus.

Expression of Nestin and IGF-1 in Rat Pancreas after Streptozotocin Administration

The present study examines whether centroacinar (CA) and intercalated duct (ICD) cells can serve as stem cells, after administration of the diabetogenic agent streptozotocin (STZ). Thirty rats were divided into five experimental groups: (1) control, (2) 1 day after STZ (STZ-1), (3) 3 days after STZ (STZ-3), (4) 7 days after STZ (STZ-7) and (5) 14 days after STZ (STZ-14). Many small pancreatic islets were observed in the STZ-7 group than in the other experimental groups, and many of these small islets were in close contact with ICD and CA cells. A higher number of nestin, insulin-like growth factor-1 (IGF-1) and IGF-1-receptor positive ICD and CA cells were observed at STZ-3 and STZ-7 than at the others. These expression patterns coincided well with the proliferating cell nuclear antigen pattern. The results suggest that rat pancreatic endocrine cells after damage by STZ administration might be recovered from newly generated cells derived from ICD and CA cells.

Notch mediates TGF alpha-induced changes in epithelial differentiation during pancreatic tumorigenesis

Notch signaling regulates cell fate decisions in a wide variety of adult and embryonic tissues. Here we show that Notch pathway components and Notch target genes are upregulated in invasive pancreatic cancer, as well as in pancreatic cancer precursors from both mouse and human. In mouse pancreas, ectopic Notch activation results in accumulation of nestin-positive precursor cells and expansion of metaplastic ductal epithelium, previously identified as a precursor lesion for pancreatic cancer. Notch is also activated as a direct consequence of EGF receptor activation in exocrine pancreas and is required for TGF alpha-induced changes in epithelial differentiation. These findings suggest that Notch mediates the tumor-initiating effects of TG alpha by expanding a population of undifferentiated precursor cells.

Centroacinar and intercalated duct cells as potential precursors of pancreatic endocrine cells in rats treated with streptozotocin

The present study examined the possibility for regeneration of pancreatic endocrine cells from centroacinar (CA) and intercalated duct (ICD) cells in rat pancreas after 5 days of continuous streptozotocin (STZ) administration. Nine rats were divided into 3 experimental groups: 1) Control group, 2) Short term recovery group; three days after STZ administration (STZ 3), and 3) Long term recovery group; ten days post-STZ administration (STZ 10). The CA and ICD cells in the STZ 3 group had swollen cytoplasm, and sometimes contained a vesicle within the core. An insulin positive signal was detected in and around the CA and ICD cells. In the STZ 3 group, cytokeratin 20 signals were co-localized with insulin signals in both CA and ICD cells. Electron microscopically, endocrine cells and small pancreatic islets were in close contact with CA and ICD cells. Systemic biophysical serum data reflected these immunohistological results. The present results suggest that CA and ICD cells are involved in the regeneration of pancreatic B cells in rats following a lesion produced by five consecutive days of STZ administration.

Differentiation and proliferation of endocrine cells in the regenerating rat pancreas after 90% pancreatectomy

The transplantation of pancreatic tissue has been anticipated to serve as a radical treatment for diabetes mellitus. However, the identification of the stem cells, and elucidation of their differential lineage and controlling mechanisms are prerequisites to ensure effective transplantation. We conducted an immunohistochemical study to determine the proliferation and differentiation dynamics of pancreatic endocrine cells in the rat pancreas 1 to 28 days after a 90% pancreatectomy. Regeneration of endocrine cells started immediately after pancreatectomy. The process of regeneration included the proliferation of preexisting islet cells and neogenesis of endocrine cells from epithelial cells of the most peripheral duct. Intercalated ductal cells and centroacinar cells were speculated to be the major sources of neogenesis, from which islet tissue was formed. Glucagon cells were the first endocrine cells differentiated, some of which transformed to insulin cells by a mechanism of non-replication. These results indicate that endocrine stem cells exist among the intercalated ductal and/or centroacinar cells, and these special regions should be utilized in transplantation for the successful treatment of diabetes.

Models of pancreatic regeneration in diabetes

The number of functionally intact beta cells in the islet organ is of decisive importance for the development, course and outcome of diabetes mellitus. Generally speaking, the total beta-cell mass reflects the balance between the renewal and loss of these cells. Assuming that virtually all forms of diabetes mellitus are characterized by an insufficient extent of beta cell replication needed to compensate for the loss or dysfunction of beta cells occurring in diabetes, elucidation of the regenerating potential in experimentally induced diabetic animal would be of interest as alternative therapy for diabetes. Here we have attempted to take a stock of different models developed in the last few years, which permit investigation of regenerative process from various angles. The review focuses on factors responsible for induction of islet neogenesis in the diabetic pancreas, ultimately leading to pancreatic regeneration and possible reversal of diabetes. On the whole the study of these models will enhance our understanding of regenerative potential of diabetic pancreas and factors necessary to trigger stem cells' population within the pancreas so as to suggest an alternative therapeutic approach for the control and/or cure of diabetes.

Expression of PGP9.5 in ductal cells of the rat pancreas during development and regeneration: can it be a marker for pancreatic progenitor cells?

The expression of protein gene product 9.5 (PGP9.5), a known neuron marker, was immunohistochemically investigated in rat pancreas. In fetal pancreas, a cluster of cells expressed PGP9.5 among the initial epithelial buds at embryonic day 11.5 (E 11.5). At E 13.5, PGP9.5 appeared among elongated and branching epithelial cells as well as along nerve fibers in the mesenchyme. On E 17.5, tubular cells became ductal cells with lumen, which strongly expressed PGP9.5. In newborn rats, ductal cells of the common bile duct (CBD) to the centroacinar cells and islet cells expressed PGP9.5. Ten days after birth, the number of the ductal cells expressing PGP9.5 was reduced, and PGP9.5-negative cells appeared in half of the duct cells. On day 21, all centroacinar cells and intercalated ductal cells became PGP9.5-negative, but some CBD and interlobular ductal cells remained positive for PGP9.5. On day 28 and thereafter, PGP9.5 was no longer detected. In a pancreatic duct ligation model, acinar cells changed to cells with duct-like structure after duct ligation. These cells strongly expressed PGP9.5 on the fifth day after duct ligation. Three to four weeks after ligation, the cells with duct-like structure changed to acinar cells, islets of Langerhans and ductal cells, but the ductal cells were PGP9.5-negative at this point. These results suggested that PGP9.5 is expressed in ductal cells that possess a potential for differentiation to pancreatic endocrine cells, and therefore can serve as a marker for the progenitor of pancreatic endocrine cells.