Are there any stem cells in the pancreas?

Introduction to stem cells

Stem cells have self-renewal capability and can proliferate and differentiate into a variety of functionally active cells that can serve in various tissues and organs. This review discusses the history, definition, and classification of stem cells. Human pluripotent stem cells (hPSCs) mainly include embryonic stem cells (hESCs) and induced pluripotent stem cells (hiPSCs). Embryonic stem cells are derived from the inner cell mass of the embryo. Induced pluripotent stem cells are derived from reprogramming somatic cells. Pluripotent stem cells have the ability to differentiate into cells derived from all three germ layers (endoderm, mesoderm, and ectoderm). Adult stem cells can be multipotent or unipotent and can produce tissue-specific terminally differentiated cells. Stem cells can be used in cell therapy to replace and regenerate damaged tissues or organs.

Concise Review: Pancreatic Cancer and Bone Marrow-Derived Stem Cells

Pancreatic adenocarcinoma remains one of the most challenging diseases of modern gastroenterology, and, even though considerable effort has been put into understanding its pathogenesis, the exact molecular mechanisms underlying the development and/or systemic progression of this malignancy still remain unclear. Recently, much attention has been paid to the potential role of bone marrow-derived stem cells (BMSCs) in this malignancy. Hence, herein, we comprehensively review the most recent discoveries and current achievements and concepts in this field. Specifically, we discuss the significance of identifying pancreatic cancer stem cells and novel therapeutic approaches involving molecular interference of their metabolism. We also describe advances in the current understanding of the biochemical and molecular mechanisms responsible for BMSC mobilization during pancreatic cancer development and systemic spread. Finally, we summarize experimental, translational, and/or clinical evidence regarding the contribution of bone marrow-derived mesenchymal stem cells, endothelial progenitor cells, hematopoietic stem/progenitor cells, and pancreatic stellate cells in pancreatic cancer development/progression. We also present their potential therapeutic value for the treatment of this deadly malignancy in humans.

SIGNIFICANCE

Different bone marrow-derived stem cell populations contribute to the development and/or progression of pancreatic cancer, and they might also be a promising "weapon" that can be used for anticancer treatments in humans. Even though the exact role of these stem cells in pancreatic cancer development and/or progression in humans still remains unclear, this concept continues to drive a completely novel scientific avenue in pancreatic cancer research and gives rise to innovative ideas regarding novel therapeutic modalities that can be safely offered to patients.

Transcriptional factors, Mafs and their biological roles

The Maf family of transcription factors is characterized by a typical bZip structure; these transcription factors act as important regulators of the development and differentiation of many organs and tissues, including the kidney. The Maf family consists of two subgroups that are characterized according to their structure: large Maf transcription factors and small Maf transcription factors. The large Maf subgroup consists of four proteins, designated as MAFA, MAFB, c-MAF and neural retina-specific leucine zipper. In particular, MAFA is a distinct molecule that has been attracting the attention of researchers because it acts as a strong transactivator of insulin, suggesting that Maf transcription factors are likely to be involved in systemic energy homeostasis. In this review, we focused on the regulation of glucose/energy balance by Maf transcription factors in various organs.

Lung cancer stem cells and low-intensity laser irradiation: a potential future therapy?

Lung cancer is notably a significant threat when considering worldwide cancer-related deaths. Despite significant advances in treatment modalities, death rates as a result of cancer relapse remain high. Relapse can occur as a result of metastasis. Cancer stem cells (CSCs) have been implicated as an important contributory factor in the development of metastasis. CSCs have the same characteristics as normal stem cells; that is, they can proliferate indefinitely and are capable of both self-renewal and differentiating into specialized cells. The molecular and cellular characteristics of stem cells and CSCs are coded for by cell-specific genes, which can be analyzed by using molecular assays setting the standard to work from. Low-intensity laser irradiation (LILI) has been applied in the treatment of numerous diseases and pathological conditions. LILI has been shown to stimulate proliferation of cells, capillary growth, and cellular metabolism as observed by adenosine triphosphate activation. It has been shown, by using different dosing levels of LILI, to either stimulate or inhibit cellular functions. One treatment strategy used on cancer cells is photodynamic therapy (PDT), in which cancer cells are treated with a photosensitizer (PS) in combination with laser irradiation. PSs are non-toxic by themselves but, with light activation, cause reactive oxygen species generation, which causes cancer cell death. Cell-specific PSs are being developed for future cancer treatment. In this review, we look at the potential effects of LILI and PDT on lung CSCs.

The potential benefit of non-purified islets preparations for islet transplantation

Since the advent of islet transplantation, there has been a significant emphasis on the importance of islet purity despite an inevitable associated loss of islet mass during the purification process. One of the key elements of the 'Edmonton Protocol' for islet transplantation published in 2000 was an emphasis on the need for sequential transplants of highly purified islets (averaging 24% beta cell purity) and the close correlation between the numbers of islets transplanted and the success of the procedure. However, the emphasis on islet purity may warrant further consideration as auto transplantation of non-purified islets currently provides the most successful insulin independence rates within the field of islet transplantation. While the role of auto and allo immunity could contribute to the differences in the success rates it is clear that within the clinical setting, significant acinar and ductal contamination is well tolerated. However, one could go further and hypothesize that extra-insular tissue including acinar tissue, ductal tissue, peri-pancreatic lymph nodes and vascular tissue actually confer an advantage to islet survival/function and may even contribute to the insulin secreting capacity of the graft post transplant. As such this review will assess the influence of extra-insular pancreatic tissue on the results of islet transplantation based on published evidence and will also explore the possibility that non-islet pancreatic cells are capable of differentiating into a beta cell phenotype in vivo contributing to an ongoing regeneration of endocrine mass during the period following transplantation.

Potential therapeutic effect of bone marrow-derived mesenchymal stem cells in acute pancreatitis

Acute pancreatitis is an inflammatory disease with dropsical, hemorrhagic or even necrotic conditions of the pancreas caused by several factors. It has significant morbidity and mortality, but no specific therapy is available so far. Bone marrow-derived mesenchymal stem cells (BMSCs) have multiple differentiation potential. They can not only differentiate to form endoderm and ectoblast cells, but also participate in tissue regeneration, repair and anti-inflammation. Recent studies have demonstrated that BMSCs have potential therapeutical effect in acute pancreatitis. BMSCs can migrate to injury tissue, multiply, be transformed to pancreatic stem cells and then participate in the process of regeneration. They also renovate vascular endothelium to improve blood circulation, adjust and control the cytokines to decrease inflammation, and regulate immunization. Here we review the recent advances in understanding the role of BMSCs in the treatment of acute pancreatitis.

Stem cell niche in the Drosophila ovary and testis; a valuable model of the intercellular signalling relationships

One of the key factors determining the function of all types of stem cells is their location in a specific microenvironment called a niche which is understood as a system of adjacent cells directly influencing their ability to carry out self-renewal divisions. The cells which compose the niche influence cytophysiological processes of stem cells both directly via the intercellular junction system and via the synthesis and release of many protein regulatory substances which are ligands of specific receptors in a particular stem cell. These proteins are often the products of distinct genes whose expression tends to be specific for niche-composing cells. The niches formed of a few cells only observed in Drosophila gonads may become a valuable functional model in the studies of mammal stem cells since their analysis proves that the preservation of the stem cells' unique features does not require a large number of cells to be present in its vicinity.

Bone marrow-derived pancreatic stellate cells in rats

Origin and fate of pancreatic stellate cells (PSCs) before, during and after pancreatic injury are a matter of debate. The crucial role of PSCs in the pathogenesis of pancreatic fibrosis is generally accepted. However, the turnover of the cells remains obscure. The present study addressed the issue of a potential bone marrow (BM) origin of PSCs. We used a model of stable hematopoietic chimerism by grafting enhanced green fluorescence protein (eGFP)-expressing BM cells after irradiation of acceptor rats. Chimerism was detected by FACS analysis of eGFP-positive cells in the peripheral blood. Dibutyltin dichloride (DBTC) was used to induce acute pancreatic inflammation with subsequent recovery over 4 weeks. Investigations have been focused on isolated cells to detect the resting PSC population. The incidence of eGFP-positive PSC obtained from the pancreas of chimeric rats was approximately 7% in healthy pancreatic tissue and increased significantly to a mean of 18% in the restored pancreas 4 weeks after DBTC-induced acute inflammation. Our results suggest that BM-derived progenitor cells represent a source of renewable stellate cells in the pancreas. Increased numbers of resting PSCs after regeneration point toward enhanced recruitment of BM-derived cells to the pancreas and/or re-acquisition of a quiescent state after inflammation-induced activation.

Isolation and in vitro cultivation turns cells from exocrine human pancreas into multipotent stem-cells

Several research groups have reported on the existence and in vitro characterization of multipotent stem-cells from the pancreas. However, the origin of these cells remains largely unexplained. Here, we report that in vitro culturing itself can turn adult cells from human exocrine pancreas into a cell population with typical stem cell characteristics. A simple, yet reliable method enabled us to track cell fates: Combining automated continuous observation using time-lapse microscopy with immunocytochemical analyses, we found that a significant fraction of the pancreatic cells ( approximately 14%) can survive trypsination and displays a drastic change in the protein expression profile. After further cultivation, these cells give rise to a heterogeneous cell population with typical multipotent stem cell characteristics; i.e. they proliferate over long time periods and continuously give rise to specialized cells from at least two germ layers. Although we cannot exclude that a rare pre-existing stem cell-type also contributes to the final in vitro-population, the majority of cells must have been arisen from mature pancreatic cells. Our findings indicate that multipotent cells for regenerative medicine, instead of being laboriously isolated, can be generated in large amounts by in vitro de-differentiation.

Islet transplantation: the quest for an ideal source

The progress of islet transplantation as a new therapy for patients with diabetes mellitus depends directly upon the development of efficient and practical immunoisolation methods for the supply of sufficient quantities of islet cells. Without these methods, large scale clinical application of this therapy would be impossible. Two eras of advances can be identified in the development of islet transplantation. The first was an era of experimental animal and human research that centered on islet isolation procedures and transplantation in different species as evidence that transplanted islets have the capability to reverse diabetes. The second was the era of the Edmonton protocol, when the focus became the standardization of isolation procedures and introduction of new immunosuppressive drugs to maintain human allograft transplantation. The quest for an alternative source for islets (xenographs, stem cells and cell cultures) to overcome the shortage of human islets was an important issue during these eras. This paper reviews the history of islet transplantation and the current procedures in human allotransplantation, as well as different types of immunoisolation methods. It explores novel approaches to enhancing transplantation site vascularity and islet cell function, whereby future immunoisolation technology could offer additional therapeutic advantages to human islet allotransplantation.

Critical issues for engineering cord blood stem cells to produce insulin

BACKGROUND/OBJECTIVES

The objectives of using cord blood stem cells for treating type 1 diabetes are simple in principle yet complex in biological and molecular mechanisms. These are defined by the complexity of the insulin-producing unit of the pancreas, the islet. Islets are composed of various cell types that arise from diverse lineages and communicate by hormones, growth factors and small-molecule mediators. These processes are regulated by integration of signal transduction pathways. While advances have been made to engineer umbilical cord blood stem cells to produce insulin, these studies only illuminate the potential of such cells to fulfil a necessary, but not sufficient, requirement for transplantation.

RESULTS/CONCLUSIONS

The challenges ahead demand detailed understanding of molecular mechanisms to move from an opportunistic, phenotypic approach to transplantation and amelioration of blood glucose, to an orderly and logical approach to a biologically and medically meaningful solution. The issues include expansion to generate large numbers of cells, self-renewal to regulate the destiny of cord blood stem cells to repopulate the hematopoietic system, and multipotency of stem cells to generate the distinct cell types of an islet.

Identification and characterization of a novel expandable adult stem/progenitor cell population in the human exocrine pancreas

It is a general opinion that tissue-specific stem cells are present in adult tissues but their specific properties remain elusive. They are rare in tissues and heterogeneous; in addition, their identification and the characterization of their progeny has encountered technical difficulties. In particular, the existence of pancreatic stem cells remains elusive because specific markers for their identification are not available. We established a method for the isolation of a population of stem/progenitor cells from the human exocrine pancreas, and propose it as a model for other human compact organs. We also used markers that identified and finally characterized these cells. Spheroids with self-replicative potential were obtained from all specimens. The isolated population contained a subset of CD34+ CD45- cells and was able to generate, in appropriate conditions, colonies that produce insulin. We obtained evidence that most freshly isolated spheroids, when co-cultured with the c-kit positive neuroblastoma cell line LAN 5, produced a c-kit positive progeny of cells larger in their cytoplasmic content than the original spheroid population, with elongated morphology resembling the neuronal phenotype. We identified a novel predominant functional type of stem/progenitor cell within the human exocrine pancreas, able to generate insulin-producing cells and potentially non-pancreatic cells.

Expression of the "stem cell marker" CD133 in pancreas and pancreatic ductal adenocarcinomas

BACKGROUND

It has been suggested that a small population of cells with unique self-renewal properties and malignant potential exists in solid tumors. Such "cancer stem cells" have been isolated by flow cytometry, followed by xenograft studies of their tumor-initiating properties. A frequently used sorting marker in these experiments is the cell surface protein CD133 (prominin-1). The aim of this work was to examine the distribution of CD133 in pancreatic exocrine cancer.

METHODS

Fifty-one cases of pancreatic ductal adenocarcinomas were clinically and histopathologically evaluated, and immunohistochemically investigated for expression of CD133, cytokeratin 19 and chromogranin A. The results were interpreted on the background of CD133 expression in normal pancreas and other normal and malignant human tissues.

RESULTS

CD133 positivity could not be related to a specific embryonic layer of organ origin and was seen mainly at the apical/endoluminal surface of non-squamous, glandular epithelia and of malignant cells in ductal arrangement. Cytoplasmic CD133 staining was observed in some non-epithelial malignancies. In the pancreas, we found CD133 expressed on the apical membrane of ductal cells. In a small subset of ductal cells and in cells in centroacinar position, we also observed expression in the cytoplasm. Pancreatic ductal adenocarcinomas showed a varying degree of apical cell surface CD133 expression, and cytoplasmic staining in a few tumor cells was noted. There was no correlation between the level of CD133 expression and patient survival.

CONCLUSION

Neither in the pancreas nor in the other investigated organs can CD133 membrane expression alone be a criterion for "stemness". However, there was an interesting difference in subcellular localization with a minor cell population in normal and malignant pancreatic tissue showing cytoplasmic expression. Moreover, since CD133 was expressed in shed ductal cells of pancreatic tumors and was found on the surface of tumor cells in vessels, this molecule may have a potential as clinical marker in patients suffering from pancreatic cancer.

Hypothetical progression model of pancreatic cancer with origin in the centroacinar-acinar compartment

OBJECTIVES

Based mainly on animal models, 2 lesions have been suggested as possible precursors of pancreatic ductal adenocarcinoma (PDAC): pancreatic intraepithelial neoplasia (PanIN) and tubular complexes (TCs). The aim of the study was to find support for either of the 2 models through the analysis of a large panel of human pancreatic tissues.

METHODS

Ninety-two PDAC, 45 chronic pancreatitis, and 27 serous cystadenoma cases were investigated using conventional morphology and immunohistochemistry.

RESULTS

Most of the cases (78% of PDAC, 93% of chronic pancreatitis, and 67% of serous cystadenoma) exhibited putative precursor lesions, predominantly TC and low-grade PanIN lesions, often present in the same tissue area. High-grade lesions were exclusively observed in PDAC specimens. In 50% to 70% of the cases with TC and associated PanIN, a transitional zone of acinar-ductular transformation with mucinous differentiation of the ductular epithelium was identified. Expression of acinar and centroacinar markers was detected in TC, in the ductular structures of the transitional zones, as well as within the epithelium of mature PanINs.

CONCLUSIONS

The results of the present study show that the coexistence of 2 different putative PDAC precursor lesions might not be a contradiction. A progression model that originates in the centroacinar-acinar compartment and ends with the development of PanIN lesions is suggested.

Directed engineering of umbilical cord blood stem cells to produce C-peptide and insulin

OBJECTIVES

In this study, we investigated the potential of umbilical cord blood stem cell lineages to produce C-peptide and insulin.

MATERIALS AND METHODS

Lineage negative, CD133+ and CD34+ cells were analyzed by flow cytometry to assess expression of cell division antigens. These lineages were expanded in culture and subjected to an established protocol to differentiate mouse embryonic stem cells (ESCs) toward the pancreatic phenotype. Phase contrast and fluorescence immunocytochemistry were used to characterize differentiation markers with particular emphasis on insulin and C-peptide.

RESULTS

All 3 lineages expressed SSEA-4, a marker previously reported to be restricted to the ESC compartment. Phase contrast microscopy showed all three lineages recapitulated the treatment-dependent morphological changes of ESCs as well as the temporally restricted expression of nestin and vimentin during differentiation. After engineering, each isolate contained both C-peptide and insulin, a result also obtained following a much shorter protocol for ESCs.

CONCLUSIONS

Since C-peptide can only be derived from de novo synthesis and processing of pre-proinsulin mRNA and protein, we conclude that these results are the first demonstration that human umbilical cord blood-derived stem cells can be engineered to engage in de novo synthesis of insulin.

Expression of Oct4, a stem cell marker, in the hamster pancreatic cancer model

BACKGROUND

Oct4 has been shown to present a stem cell marker that is expressed in embryonic cells and in germ cell tumors. Recently, its expression in a few human tissues and cancer cells has been reported. Because in the hamster pancreatic cancer model most tumors develop from within islets presumably from stem cells, we investigated the expression of Oct4 in this model.

METHODS

Two normal pancreases and 15 pancreatic cancers induced by N-nitrosobis(2-oxypropyl)amine (BOP) were processed for immunohistochemistry using a monoclonal Oct4 antibody at a concentration of 1:500.

RESULTS

In the normal pancreas, Oct4 was expressed only in islet cells in a diffuse cytoplasmic pattern. No nuclear staining was found in any cells. In 14 of the pancreatic cancers, nuclear staining was detected in many cells or in small foci. Diffuse cytoplasmic but no nuclear staining was found in one tumor and a mixed Golgi type and nuclear staining in two cases. Nuclear staining was also identified in early intrainsular ductular and in Ca in situ lesions.

CONCLUSIONS

BOP reactivates the Oct4 gene and can be considered an early tumor marker in this model.

Potential roles of large mafs in cell lineages and developing pancreas

OBJECTIVES

Maf is a family of transcription factor proteins characterized by a typical bZip structure, and mafA, a member of the large-maf family, is a strong transactivator of insulin in cell lines. The present study investigated the expression profiles of the large-maf family proteins in porcine pancreatic tissue and in primary culture cells.

METHODS

Immunohistochemical staining was performed to localize each maf protein. Messenger RNA expression was quantitated by real-time polymerase chain reaction, and protein expression was assessed by Western blotting.

RESULTS

Islet formation was not as clear in newborn pancreatic tissue as in adult pancreatic tissue. MafA- and c-maf-positive cells were more diffusely localized in pancreatic tissue with fewer mafB-positive cell clusters scattered throughout. By contrast, islet formation was clearer, and positive staining for mafA and c-maf tended to be more prominent in the islets of adult pancreatic tissue. Messenger RNA and protein expressions were consistent with the immunohistochemical findings. MafA, mafB, and c-maf coexpressed with insulin-positive cells, and c-maf coexpressed with glucagon-positive cells in adult porcine pancreas based on the results of a double-staining study.

CONCLUSIONS

Large mafs were identified in normal porcine and human pancreas, and the expression levels and localizations of the large mafs in newborn and adult pancreatic tissues differed. Mafs may play important roles in establishing endocrine function during pancreatic cell differentiation.

Prospective and challenges of islet transplantation for the therapy of autoimmune diabetes

Pancreatic islet cell transplantation is an attractive treatment of type 1 diabetes (T1D). The success enhanced by the Edmonton protocol has fostered phenomenal progress in the field of clinical islet transplantation in the past 5 years, with 1-year rates of insulin independence after transplantation near 80%. Long-term function of the transplanted islets, however, even under the Edmonton protocol, seems difficult to accomplish, with only 10% of patients maintaining insulin independence 5 years after transplantation. These results differ from the higher metabolic performance achieved by whole pancreas allotransplantation, and autologous islet cell transplantation, and form the basis for a limited applicability of islet allografts to selected adult patients. Candidate problems in islet allotransplantation deal with alloimmunity, autoimmunity, and the need for larger islet cell masses. Employment of animal islets and stem cells, as alternative sources of insulin production, will be considered to face the problem of human tissue shortage. Emerging evidence of the ability to reestablish endogenous insulin production in the pancreas even after the diabetic damage occurs envisions the exogenous supplementation of islets to patients also as a temporary therapeutic aid, useful to buy time toward a possible self-healing process of the pancreatic islets. All together, islet cell transplantation is moving forward.

The potential for stem cell therapy in diabetes

Both type 1 and type 2 diabetes are characterized by a marked deficit in beta-cell mass causing insufficient insulin secretion. Beta-cell replacement strategies may eventually provide a cure for diabetes. Current therapeutic approaches include pancreas and islet transplantation, but the chronic shortage of donor organs restricts this treatment option to a small proportion of affected patients. Moreover, recent evidence shows a progressive decline in beta-cell function after islet transplantation so that most patients have to revert to insulin treatment within a few years. In this article recent progress in the generation, culture and targeted differentiation of human embryonic stem (ES) cells is reviewed, and some of the issues surrounding their use as a source of beta-cells are discussed.