Phenotypic determination and characterization of nestin-positive precursors derived from human fetal pancreas

Multipotent fetal stem cells in reproductive biology research

Due to the limited accessibility of the in vivo situation, the scarcity of the human tissue, legal constraints, and ethical considerations, the underlying molecular mechanisms of disorders, such as preeclampsia, the pathological consequences of fetomaternal microchimerism, or infertility, are still not fully understood. And although substantial progress has already been made, the therapeutic strategies for reproductive system diseases are still facing limitations. In the recent years, it became more and more evident that stem cells are powerful tools for basic research in human reproduction and stem cell-based approaches moved into the center of endeavors to establish new clinical concepts. Multipotent fetal stem cells derived from the amniotic fluid, amniotic membrane, chorion leave, Wharton´s jelly, or placenta came to the fore because they are easy to acquire, are not associated with ethical concerns or covered by strict legal restrictions, and can be banked for autologous utilization later in life. Compared to adult stem cells, they exhibit a significantly higher differentiation potential and are much easier to propagate in vitro. Compared to pluripotent stem cells, they harbor less mutations, are not tumorigenic, and exhibit low immunogenicity. Studies on multipotent fetal stem cells can be invaluable to gain knowledge on the development of dysfunctional fetal cell types, to characterize the fetal stem cells migrating into the body of a pregnant woman in the context of fetomaternal microchimerism, and to obtain a more comprehensive picture of germ cell development in the course of in vitro differentiation experiments. The in vivo transplantation of fetal stem cells or their paracrine factors can mediate therapeutic effects in preeclampsia and can restore reproductive organ functions. Together with the use of fetal stem cell-derived gametes, such strategies could once help individuals, who do not develop functional gametes, to conceive genetically related children. Although there is still a long way to go, these developments regarding the usage of multipotent fetal stem cells in the clinic should continuously be accompanied by a wide and detailed ethical discussion.

A, B, C's of Trk Receptors and Their Ligands in Ocular Repair

Neurotrophins are a family of closely related secreted proteins that promote differentiation, development, and survival of neurons, which include nerve growth factor (NGF), brain-derived neurotrophic factor, neurotrophin-3, and neurotrophin-4. All neurotrophins signal through tropomyosin receptor kinases (TrkA, TrkB, and TrkC) which are more selective to NGF, brain-derived neurotrophic factor, and neurotrophin-3, respectively. NGF is the most studied neurotrophin in the ocular surface and a human recombinant NGF has reached clinics, having been approved to treat neurotrophic keratitis. Brain-derived neurotrophic factor, neurotrophin-3, and neurotrophin-4 are less studied neurotrophins in the ocular surface, even though brain-derived neurotrophic factor is well characterized in glaucoma, retina, and neuroscience. Recently, neurotrophin analogs with panTrk activity and TrkC selectivity have shown promise as novel drugs for treating dry eye disease. In this review, we discuss the biology of the neurotrophin family, its role in corneal homeostasis, and its use in treating ocular surface diseases. There is an unmet need to investigate parenteral neurotrophins and its analogs that activate TrkB and TrkC selectively.

Activation of Pancreatic Stellate Cells Is Beneficial for Exocrine but Not Endocrine Cell Differentiation in the Developing Human Pancreas

Pancreatic stellate cells (PaSCs) are non-endocrine, mesenchymal-like cells that reside within the peri-pancreatic tissue of the rodent and human pancreas. PaSCs regulate extracellular matrix (ECM) turnover in maintaining the integrity of pancreatic tissue architecture. Although there is evidence indicating that PaSCs are involved in islet cell survival and function, its role in islet cell differentiation during human pancreatic development remains unclear. The present study examines the expression pattern and functional role of PaSCs in islet cell differentiation of the developing human pancreas from late 1st to 2nd trimester of pregnancy. The presence of PaSCs in human pancreata (8–22 weeks of fetal age) was characterized by ultrastructural, immunohistological, quantitative RT-PCR and western blotting approaches. Using human fetal PaSCs derived from pancreata at 14–16 weeks, freshly isolated human fetal islet-epithelial cell clusters (hIECCs) were co-cultured with active or inactive PaSCs in vitro. Ultrastructural and immunofluorescence analysis demonstrated a population of PaSCs near ducts and newly formed islets that appeared to make complex cell-cell dendritic-like contacts. A small subset of PaSCs co-localized with pancreatic progenitor-associated transcription factors (PDX1, SOX9, and NKX6-1). PaSCs were highly proliferative, with significantly higher mRNA and protein levels of PaSC markers (desmin, αSMA) during the 1st trimester of pregnancy compared to the 2nd trimester. Isolated human fetal PaSCs were identified by expression of stellate cell markers and ECM. Suppression of PaSC activation, using all-trans retinoic acid (ATRA), resulted in reduced PaSC proliferation and ECM proteins. Co-culture of hIECCs, directly on PaSCs or indirectly using Millicell^® Inserts or using PaSC-conditioned medium, resulted in a reduction the number of insulin⁺ cells but a significant increase in the number of amylase⁺ cells. Suppression of PaSC activation or Notch activity during the co-culture resulted in an increase in beta-cell differentiation. This study determined that PaSCs, abundant during the 1st trimester of pancreatic development but decreased in the 2nd trimester, are located near ductal and islet structures. Direct and indirect co-cultures of hIECCs with PaSCs suggest that activation of PaSCs has opposing effects on beta-cell and exocrine cell differentiation during human fetal pancreas development, and that these effects may be dependent on Notch signaling.

PDX1- /NKX6.1+ progenitors derived from human pluripotent stem cells as a novel source of insulin-secreting cells

AIM

Beta cell replacement strategies are a promising alternative for diabetes treatment. Human pluripotent stem cells (hPSCs) serve as a scalable source for producing insulin-secreting cells for transplantation therapy. We recently generated novel hPSC-derived pancreatic progenitors, expressing high levels of the transcription factor NKX6.1, in the absence of PDX1 (PDX1^- /NKX6.1⁺ ). Herein, our aim was to characterize this novel population and assess its ability to differentiate into insulin-secreting beta cells in vitro.

MATERIALS AND METHODS

Three different hPSC lines were differentiated into PDX1^- /NKX6.1⁺ progenitors, which were further differentiated into insulin-secreting cells using two different protocols. The progenitors and beta cells were extensively characterized. Transcriptome analysis was performed at different stages and compared with the profiles of various pancreatic counterparts.

RESULTS

PDX1^- /NKX6.1⁺ progenitors expressed high levels of nestin, a key marker of pancreatic islet-derived progenitors, in the absence of E-cadherin, similar to pancreatic mesenchymal stem cells. At progenitor stage, comparison of the two populations showed downregulation of pancreatic epithelial genes and upregulation of neuronal development genes in PDX1^- /NKX6.1⁺ cells in comparison to the PDX1⁺ /NKX6.1⁺ cells. Interestingly, on further differentiation, PDX1^- /NKX6.1⁺ cells generated mono-hormonal insulin⁺ cells and activated pancreatic key genes, such as PDX1. The transcriptome profile of PDX1^- /NKX6.1⁺ -derived beta (3D-beta) was closely similar to those of human pancreatic islets and purified hPSC-derived beta cells. Also, the 3D-beta cells secreted C-peptide in response to increased glucose concentrations indicating their functionality.

CONCLUSION

These findings provide a novel source of insulin-secreting cells that can be used for beta cell therapy for diabetes.

Current progress in stem cell therapy for type 1 diabetes mellitus

Type 1 diabetes mellitus (T1DM) is the most common chronic autoimmune disease in young patients and is characterized by the loss of pancreatic β cells; as a result, the body becomes insulin deficient and hyperglycemic. Administration or injection of exogenous insulin cannot mimic the endogenous insulin secreted by a healthy pancreas. Pancreas and islet transplantation have emerged as promising treatments for reconstructing the normal regulation of blood glucose in T1DM patients. However, a critical shortage of pancreases and islets derived from human organ donors, complications associated with transplantations, high cost, and limited procedural availability remain bottlenecks in the widespread application of these strategies. Attempts have been directed to accommodate the increasing population of patients with T1DM. Stem cell therapy holds great potential for curing patients with T1DM. With the advent of research on stem cell therapy for various diseases, breakthroughs in stem cell-based therapy for T1DM have been reported. However, many unsolved issues need to be addressed before stem cell therapy will be clinically feasible for diabetic patients. In this review, we discuss the current research advances in strategies to obtain insulin-producing cells (IPCs) from different precursor cells and in stem cell-based therapies for diabetes.

Pancreatic Stellate Cells: A Rising Translational Physiology Star as a Potential Stem Cell Type for Beta Cell Neogenesis

The progressive decline and eventual loss of islet β-cell function underlies the pathophysiological mechanism of the development of both type 1 and type 2 diabetes mellitus. The recovery of functional β-cells is an important strategy for the prevention and treatment of diabetes. Based on similarities in developmental biology and anatomy, in vivo induction of differentiation of other types of pancreatic cells into β-cells is a promising avenue for future diabetes treatment. Pancreatic stellate cells (PSCs), which have attracted intense research interest due to their effects on tissue fibrosis over the last decade, express multiple stem cell markers and can differentiate into various cell types. In particular, PSCs can successfully differentiate into insulin- secreting cells in vitro and can contribute to tissue regeneration. In this article, we will brings together the main concepts of the translational physiology potential of PSCs that have emerged from work in the field and discuss possible ways to develop the future renewable source for clinical treatment of pancreatic diseases.

Human mesenchymal stem cells - current trends and future prospective

Stem cells are cells specialized cell, capable of renewing themselves through cell division and can differentiate into multi-lineage cells. These cells are categorized as embryonic stem cells (ESCs), induced pluripotent stem cells (iPSCs) and adult stem cells. Mesenchymal stem cells (MSCs) are adult stem cells which can be isolated from human and animal sources. Human MSCs (hMSCs) are the non-haematopoietic, multipotent stem cells with the capacity to differentiate into mesodermal lineage such as osteocytes, adipocytes and chondrocytes as well ectodermal (neurocytes) and endodermal lineages (hepatocytes). MSCs express cell surface markers like cluster of differentiation (CD)29, CD44, CD73, CD90, CD105 and lack the expression of CD14, CD34, CD45 and HLA (human leucocyte antigen)-DR. hMSCs for the first time were reported in the bone marrow and till now they have been isolated from various tissues, including adipose tissue, amniotic fluid, endometrium, dental tissues, umbilical cord and Wharton's jelly which harbours potential MSCs. hMSCs have been cultured long-term in specific media without any severe abnormalities. Furthermore, MSCs have immunomodulatory features, secrete cytokines and immune-receptors which regulate the microenvironment in the host tissue. Multilineage potential, immunomodulation and secretion of anti-inflammatory molecules makes MSCs an effective tool in the treatment of chronic diseases. In the present review, we have highlighted recent research findings in the area of hMSCs sources, expression of cell surface markers, long-term in vitro culturing, in vitro differentiation potential, immunomodulatory features, its homing capacity, banking and cryopreservation, its application in the treatment of chronic diseases and its use in clinical trials.

Nestin involvement in tissue injury and cancer--a potential tumor marker?

BACKGROUND

In eukaryotic cells, the cytoskeleton contains three major filamentous components: actin microfilaments, microtubules and intermediate filaments. Nestin represents one of the class VI intermediate filament proteins. Clinical and molecular analyses have revealed substantial information regarding the presence of Nestin in cells with progenitor or stem cell properties. During tissue injury Nestin is expressed in cells with progenitor cell-like properties. These cells may serve as a tissue reserve and, as such, may contribute to tissue repair. Based on currently available data, Nestin also appears to be implicated in two oncogenic processes. First, Nestin has been found to be expressed in cancer stem-like cells and poorly differentiated cancer cells and, as such, Nestin is thought to contribute to the aggressive behavior of these cells. Second, Nestin has been found to be involved in tumor angiogenesis through an interaction of cancer cells and blood vessel endothelial cells and, as such, Nestin is thought to facilitate tumor growth.

CONCLUSIONS

We conclude that Nestin may serve as a promising tumor marker and as a potential therapeutic target amenable to tumor suppression and angiogenesis inhibition.

Current status of regeneration of pancreatic β-cells

Newly generated insulin‐secreting cells for use in cell therapy for insulin‐deficient diabetes mellitus require properties similar to those of native pancreatic β‐cells. Pancreatic β‐cells are highly specialized cells that produce a large amount of insulin, and secrete insulin in a regulated manner in response to glucose and other stimuli. It is not yet explained how the β‐cells acquire this complex function during normal differentiation. So far, in vitro generation of insulin‐secreting cells from embryonic stem cells, induced‐pluripotent stem cells and adult stem/progenitor‐like cells has been reported. However, most of these cells are functionally immature and show poor glucose‐responsive insulin secretion compared to that of native pancreatic β‐cells (or islets). Strategies to generate functional β‐cells or a whole organ in vivo have also recently been proposed. Establishing a protocol to generate fully functional insulin‐secreting cells that closely resemble native β‐cells is a critical matter in regenerative medicine for diabetes. Understanding the physiological processes of differentiation, proliferation and regeneration of pancreatic β‐cells might open the path to cell therapy to cure patients with absolute insulin deficiency.

Clinical applications of mesenchymal stem cells in chronic diseases

Extraordinary progress in understanding several key features of stem cells has been made in the last ten years, including definition of the niche, and identification of signals regulating mobilization and homing as well as partial understanding of the mechanisms controlling self-renewal, commitment, and differentiation. This progress produced invaluable tools for the development of rational cell therapy protocols that have yielded positive results in preclinical models of genetic and acquired diseases and, in several cases, have entered clinical experimentation with positive outcome. Adult mesenchymal stem cells (MSCs) are nonhematopoietic cells with multilineage potential to differentiate into various tissues of mesodermal origin. They can be isolated from bone marrow and other tissues and have the capacity to extensively proliferate in vitro. Moreover, MSCs have also been shown to produce anti-inflammatory molecules which can modulate humoral and cellular immune responses. Considering their regenerative potential and immunoregulatory effect, MSC therapy is a promising tool in the treatment of degenerative, inflammatory, and autoimmune diseases. It is obvious that much work remains to be done to increase our knowledge of the mechanisms regulating development, homeostasis, and tissue repair and thus to provide new tools to implement the efficacy of cell therapy trials.

Present and future cell therapies for pancreatic beta cell replenishment

If only at a small scale, islet transplantation has successfully addressed what ought to be the primary endpoint of any cell therapy: the functional replenishment of damaged tissue in patients. After years of less-than-optimal approaches to immunosuppression, recent advances consistently yield long-term graft survival rates comparable to those of whole pancreas transplantation. Limited organ availability is the main hurdle that stands in the way of the widespread clinical utilization of this pioneering intervention. Progress in stem cell research over the past decade, coupled with our decades-long experience with islet transplantation, is shaping the future of cell therapies for the treatment of diabetes. Here we review the most promising avenues of research aimed at generating an inexhaustible supply of insulin-producing cells for islet regeneration, including the differentiation of pluripotent and multipotent stem cells of embryonic and adult origin along the beta cell lineage and the direct reprogramming of non-endocrine tissues into insulin-producing cells.

Concise review: mesenchymal stem cells for diabetes

Mesenchymal stem cells (MSCs) have already made their mark in the young field of regenerative medicine. Easily derived from many adult tissues, their therapeutic worth has already been validated for a number of conditions. Unlike embryonic stem cells, neither their procurement nor their use is deemed controversial. Here we review the potential use of MSCs for the treatment of type 1 diabetes mellitus, a devastating chronic disease in which the insulin-producing cells of the pancreas (the β-cells) are the target of an autoimmune process. It has been hypothesized that stem cell-derived β-cells may be used to replenish the islet mass in diabetic patients, making islet transplantation (a form of cell therapy that has already proven effective at clinically restoring normoglycemia) available to millions of prospective patients. Here we review the most current advances in the design and application of protocols for the differentiation of transplantable β-cells, with a special emphasis in analyzing MSC potency according to their tissue of origin. Although no single method appears to be ripe enough for clinical trials yet, recent progress in reprogramming (a biotechnological breakthrough that relativizes the thus far insurmountable barriers between embryonal germ layers) bodes well for the rise of MSCs as a potential weapon of choice to develop personalized therapies for type 1 diabetes.

Insulin-producing cells from human pancreatic islet-derived progenitor cells following transplantation in mice

Stem/progenitor cells hold promise for alleviating/curing type 1 diabetes due to the capacity to differentiate into functional insulin-producing cells. The current study aims to assess the differentiation potential of human pancreatic IPCs (islet-derived progenitor cells). IPCs were derived from four human donors and subjected to more than 2000-fold expansion before turning into ICCs (islet-like cell clusters). The ICCs expressed ISL-1 Glut2, PDX-1, ngn3, insulin, glucagon and somatostatin at the mRNA level and stained positive for insulin and glucagon by immunofluorescence. Following glucose challenge in vitro, C-peptide was detected in the sonicated ICCs, instead of in the conditioned medium. To examine the function of the cells in vivo, IPCs or ICCs were transplanted under the renal capsule of immunodeficient mice. One month later, 19 of 28 mice transplanted with ICCs and 4 of 14 mice with IPCs produced human C-peptide detectable in blood, indicating that the in vivo environment further facilitated the maturation of ICCs. However, among the hormone-positive mice, only 9 of 19 mice with ICCs and two of four mice with IPCs were able to secrete C-peptide in response to glucose.

Extrinsic factors involved in the differentiation of stem cells into insulin-producing cells: an overview

Diabetes mellitus is a chronic disease with many debilitating complications. Treatment of diabetes mellitus mainly revolves around conventional oral hypoglycaemic agents and insulin replacement therapy. Recently, scientists have turned their attention to the generation of insulin-producing cells (IPCs) from stem cells of various sources. To date, many types of stem cells of human and animal origins have been successfully turned into IPCs in vitro and have been shown to exert glucose-lowering effect in vivo. However, scientists are still faced with the challenge of producing a sufficient number of IPCs that can in turn produce sufficient insulin for clinical use. A careful choice of stem cells, methods, and extrinsic factors for induction may all be contributing factors to successful production of functional beta-islet like IPCs. It is also important that the mechanism of differentiation and mechanism by which IPCs correct hyperglycaemia are carefully studied before they are used in human subjects.

Experimental evidence supporting the lack of primary stem cells in adult pancreatic tissue

PURPOSE

To investigate the origin and localization of pancreatic stem cells in adult pancreatic tissues and to determine the primary mechanism underlying the participation of these cells in repairing pancreatic injuries.

METHODS

Sprague-Dawley rats were divided into experimental and control groups. The experimental group was given intraperitoneal injections of cerulein to induce acute pancreatitis. At 6 h, 1, 2, 3, 5 and 7 days, 5 rats from the experimental group and 2 rats from the control group were sacrificed; all sacrificed animals were intraperitoneally injected with 5-bromo-2'-deoxyuracil nucleotides (BrdU) 6 and 3 h prior to sacrifice. The pathological changes of pancreatic tissue were observed. The stem cell marker nestin and the cell proliferation marker BrdU were detected with immunohistochemistry. Pancreatic duodenal homeobox-1 (PDX-1) was determined by real-time PCR.

RESULTS

(1) The pathological changes of acute pancreatitis can be divided into three phases: the edema and apoptosis phase, the hemorrhagic necrosis phase, and the reconstruction phase. (2) Nestin-positive cells mainly appeared in the interlobular vascular lumen after cerulein injection, and they peaked at day 3 when the positive cells spread all over the pancreatic tissues. (3) BrdU-positive cells began to appear in the area surrounding the interlobular region, and the number of positive cells peaked on day 7. (4) The expression of PDX-1 mRNA initially increased, then decreased and gradually got close to a normal level.

CONCLUSION

Primary pancreatic stem cells may not exist in the adult pancreatic tissues. The so-called pancreatic stem cells may actually originate from bone marrow stem cells. When pancreatic tissue is injured, bone marrow stem cells may participate in the repair.

Persistent circulating human insulin in sheep transplanted in utero with human mesenchymal stem cells

OBJECTIVE

To determine if mesenchymal stem cells (MSC) derived from human fetal pancreatic tissue (pMSC) would engraft and differentiate in sheep pancreas following transplantation in utero.

MATERIALS AND METHODS

A three-step culture system was established for generating human fetal pMSC. Sheep fetuses were transplanted during the fetal transplant receptivity period with human pMSC and evaluated for in situ and functional engraftment in their pancreas, liver, and bone marrow.

RESULTS

Isolation and expansion of adherent cells from the human fetal pancreas yielded a cell population with morphologic and phenotypic characteristics similar to MSC derived from bone marrow. This putative stem cell population could undergo multilineage differentiation in vitro. Three to 27 months after fetal transplantation, the pancreatic engraftment frequency (chimeric index) was 79%, while functional engraftment was noted in 50% of transplanted sheep. Hepatic and marrow engraftment and expression was noted as well.

CONCLUSION

We have established a procedure for isolation of human fetal pMSC that display characteristics similar to bone marrow-derived MSC. In vivo results suggest the pMSC engraft, differentiate, and secrete human insulin from the sheep pancreas.

Identification of a pancreatic stellate cell population with properties of progenitor cells: new role for stellate cells in the pancreas

Numerous studies conducted in a diversity of adult tissues have shown that certain stem cells are characterized by the expression of a protein known as the ABCG2 transporter (where ABC is ATP- binding cassette). In the adult pancreas, although various multipotent progenitors have been proposed, the ABCG2 marker has only been detected in the so-called 'side population' (a primitive haematopoietic cell population with a multipotential capacity). In the present study we sought to identify new ABCG2+ pancreatic cell populations and to explore whether they exhibit the properties of progenitor cells. We isolated and expanded mitoxantrone-resistant cells from pancreata of lactating rats by drug selection. These cells were characterized and maintained in different stages of differentiation using several media 'cocktails' plus Matrigel (BD Biosciences). Differentiation was assessed by RT-PCR (reverse transcription-PCR), immunocytochemistry, electron microscopy and ELISA. The expanded cell population demonstrated a phenotype of PaSCs (pancreatic stellate cells). Spontaneous cell clusters occurred during cell expansion and they showed weak expression of the transcription factor Pdx1 (pancreatic and duodenal homeobox 1). Moreover, the presence of inductive factors in the Matrigel plus exendin-4 led to an increase in Pdx1 and endocrine genes, such as insulin, islet amyloid polypeptide, glucagon, the glucose transporter GLUT2, chromogranin A and the convertases PC1/3 and PC2 were also detected. Immunocytochemical analysis showed co-localization of insulin and C-peptide, whereas ultrastructural studies revealed the presence of granules. Insulin secretion from cell clusters was detected in the cell culture medium. We identified a population of PaSCs that express the ABCG2+ transporter and have the capacity to transdifferentiate into insulin-producing cells. Although the potential therapeutic application remains to be tested, PaSCs could represent a future option for insulin replacement in diabetes research.

Oct4 is expressed in Nestin-positive cells as a marker for pancreatic endocrine progenitor

There are abundant progenitor cells in the developing pancreas, but molecular markers for these cells are lacking. Octamer-binding transcription factor-4 (Oct4) is an important transcription factor for keeping the features of self-renewal and pluripotency of embryonic stem cells. It's well known that Oct4, as a totipotent stem cells marker, just is expressed in totipotent stem cells. In the present study, we collected ten human fetal pancreases, and found that Oct4 mRNA and protein were expressed in human fetal pancreas samples by RT-PCR, western blot and immunohistochemistry assays. Using double-staining, we demonstrated that Oct4 was not co-expressed with Chromogranin A (a peptide expressed in endocrine cells), but partially co-expressed with Ngn3 (a transcription factor expressed in pancreatic endocrine precursor cells) and Nestin (a intermediate filament, Nestin-positive cells isolated from islets can be induced to express insulin) in human fetal pancreases. Indeed, we prepared Nestin-positive cells from human fetal pancreas by cell selection, and found that these cells expressed Oct4 and Ngn3. The Nestin-positive cells displayed a rapid duplication and could differentiate into osteoblasts, fat and endocrine cells in vitro. These results indicated that the Nestin-positive cells in the fetal age should be pancreatic progenitor cells. Overall, our study suggested that Oct4 was a marker for pancreatic endocrine progenitor.

Immunolocalization of nestin in pancreatic tissue of mice at different ages

AIM: To localize nestin positive cells (NPC) in pancreatic tissue of mice of different ages.

METHODS: Paraffin sections of 6-8 μm of fixed pancreatic samples were mounted on poly-L-lysine coated slides and used for Immunolocalization using appropriate primary antibodies (Nestin, Insulin, Glucagon), followed by addition of a fluorescently labeled secondary antibody. The antigen-antibody localization was captured using a confocal microscope (Leica SP 5 series).

RESULTS: In 3-6 d pups, the NPC were localized towards the periphery of the endocrine portion, as evident from immunolocalization of insulin and glucagon, while NPC were absent in the acinar portion. At 2 wk, NPC were localized in both the exocrine and endocrine portions. Interestingly, in 4-wk-old mice NPC were seen only in the endocrine portion, towards the periphery, and were colocalized with the glucagon positive cells. In the pancreas of 8- wk-old mice, the NPC were predominantly localized in the central region of the islet clusters, where immunostaining for insulin was at a maximum.

CONCLUSION: We report for the first time the immunolocalization of NPC in the pancreas of mice of different ages (3 d to 8 wk) with reference to insulin and glucagon positive cells. The heterogeneous localization of the NPC observed may be of functional and developmental significance and suggest(s) that mice pancreatic tissue can be a potential source of progenitor cells. NPC from the pancreas can be isolated, proliferated and programmed to differentiate into insulin secreting cells under the appropriate microenvironment.

Neuron-like differentiation and selective ablation of undifferentiated embryonic stem cells containing suicide gene with Oct-4 promoter

In vivo transplantation of undifferentiated embryonic stem (ES) cells can produce teratomas with uncontrolled cell proliferation. Although ES cells may be attractive candidates for human cell-replacement therapy in the future, the major limitation of its application to the therapy is teratoma formation. In the present study, ES cells containing herpes simplex virus-thymidine kinase (HSV-tk) transgene for a suicide gene expression under the control of the Oct-4 promoter was used for ablation of undifferentiated ES cells, which may produce teratomas, using three-dimensional cell culture system allowing a multilayer cell construct. Selective ablation of undifferentiated ES cells expressing HSV-tk gene under the control of Oct-4 promoter was achieved by ganciclovir treatment. Surviving ES cells after ganciclovir treatment expressed several neuron-associated markers such as synaptophysin, beta-tubulin, vesicular glutamate transporter 1, syntaxin, protein kinase C and glial fibrillary acidic protein (GFAP) but not Oct-4. Coexpression of synaptophysin as a marker of neuronal synapse and GFAP as that of glial fibers in the surviving ES cells revealed finely structured neuronal network. Furthermore, decrease of Ki-67 proliferative index was detected in the surviving ES cells. In conclusion, selective ablation of undifferentiated ES cells by a suicide gene decreases proliferative activity and induces neuron-like differentiation in ES cells.

Diabetes mellitus: an opportunity for therapy with stem cells?

In both Type 1 and 2 diabetes, insufficient numbers of insulin-producing beta-cells are a major cause of defective control of blood glucose and its complications. Restoration of damaged beta-cells by endocrine pancreas regeneration would be an ideal therapeutic option. The possibility of generating insulin-secreting cells with adult pancreatic stem or progenitor cells has been investigated extensively. The conversion of differentiated cells such as hepatocytes into beta-cells is being attempted using molecular insights into the transcriptional make-up of beta-cells. Additionally, the enhanced proliferation of beta-cells in vivo or in vitro is being pursued as a strategy for regenerative medicine for diabetes. Advances have also been made in directing the differentiation of embryonic stem cells into beta-cells. Although progress is encouraging, major gaps in our understanding of developmental biology of the pancreas and adult beta-cell dynamics remain to be bridged before a therapeutic application is made possible.

Beta-cell replacement and regeneration: Strategies of cell-based therapy for type 1 diabetes mellitus

Pancreatic islet transplantation has demonstrated that long-term insulin independence may be achieved in patients suffering from diabetes mellitus type 1. However, because of limited availability of islet tissue, new sources of insulin producing cells that are responsive to glucose are required. Development of pancreatic beta-cell lines from rodent or human origin has progressed slowly in recent years. Current experiments for ex vivo expansion of beta cells and in vitro differentiation of embryonic and adult stem cells into insulin producing beta-cell phenotypes led to promising results. Nevertheless, the cells generated to date lack important characteristics of mature beta cells and generally display reduced insulin secretion and loss of proliferative capacity. Therefore, much better understanding of the mechanisms that regulate expansion and differentiation of stem/progenitor cells is necessary. Here, we review recent advances in the identification of potential cellular sources, and the development of strategies to regenerate or fabricate insulin producing and glucose sensing cells that might enable future cell-based therapies of diabetes mellitus type 1.

Mesenchymal stem cells: biology and clinical potential in type 1 diabetes therapy

Mesenchymal stem cells (MSCs) can be derived from adult bone marrow, fat and several foetal tissues. In vitro, MSCs have the capacity to differentiate into multiple mesodermal and non-mesodermal cell lineages. Besides, MSCs possess immunosuppressive effects by modulating the immune function of the major cell populations involved in alloantigen recognition and elimination. The intriguing biology of MSCs makes them strong candidates for cell-based therapy against various human diseases. Type 1 diabetes is caused by a cell-mediated autoimmune destruction of pancreatic β-cells. While insulin replacement remains the cornerstone treatment for type 1 diabetes, the transplantation of pancreatic islets of Langerhans provides a cure for this disorder. And yet, islet transplantation is limited by the lack of donor pancreas. Generation of insulin-producing cells (IPCs) from MSCs represents an attractive alternative. On the one hand, MSCs from pancreas, bone marrow, adipose tissue, umbilical cord blood and cord tissue have the potential to differentiate into IPCs by genetic modification and/or defined culture conditions In vitro. On the other hand, MSCs are able to serve as a cellular vehicle for the expression of human insulin gene. Moreover, protein transduction technology could offer a novel approach for generating IPCs from stem cells including MSCs. In this review, we first summarize the current knowledge on the biological characterization of MSCs. Next, we consider MSCs as surrogate β-cell source for islet transplantation, and present some basic requirements for these replacement cells. Finally, MSCs-mediated therapeutic neovascularization in type 1 diabetes is discussed.

Human chorionic gonadotropin induces nestin expression in endothelial cells of the ovary via vascular endothelial growth factor signaling

The intermediate filament protein nestin was originally found to be expressed in neuronal progenitor cells, but recent studies have shown that other cell types, including endocrine and vascular endothelial cells, express nestin. In the present study, we examined the expression and localization of nestin in the ovaries of developing, peripubertal, and adult rats. RT-PCR and Western blot analyses revealed that nestin mRNA and proteins were expressed in adult rat ovaries. Immunohistochemical analyses using adult rat ovaries showed that nestin was mainly localized to capillary endothelial cells of theca interna in follicles with more than two layers of granulosa cells and that its expression increased with follicle growth. Ontogenetically, ovarian nestin expression started at the peripubertal period when the first gonadotropin surge occurs. To test the possibility that gonadotropins induce nestin expression, prepubertal (postnatal d 21) rats were sc injected with equine chorionic gonadotropin (eCG) and/or human chorionic gonadotropin (hCG). A single injection of hCG, but not eCG, was sufficient to induce nestin expression in follicles, mainly in capillary endothelial cells of theca interna. Furthermore, pretreatment with an inhibitor of vascular endothelial growth factor receptor prevented the induction of the nestin expression by hCG. These findings demonstrate that the endogenous LH surge induces nestin expression in capillary endothelial cells of theca interna via the vascular endothelial growth factor signaling pathway. Nestin may be involved in angiogenesis in growing follicles, which is followed by follicle maturation and subsequent ovulation.

Stem cell potential for type 1 diabetes therapy

Stem cells have been considered as a useful tool in Regenerative Medicine due to two main properties: high rate of self-renewal, and their potential to differentiate into all cell types present in the adult organism. Depending on their origin, these cells can be grouped into embryonic or adult stem cells. Embryonic stem cells are obtained from the inner cell mass of blastocyst, which appears during embryonic day 6 of human development. Adult stem cells are present within various tissues of the organism and are responsible for their turnover and repair. In this sense, these cells open new therapeutic possibilities to treat degenerative diseases such as type 1 diabetes. This pathology is caused by the autoimmune destruction of pancreatic β-cells, resulting in the lack of insulin production. Insulin injection, however, cannot mimic β-cell function, thus causing the development of important complications. The possibility of obtaining β-cell surrogates from either embryonic or adult stem cells to restore insulin secretion will be discussed in this review.

Stem/Progenitor cell sources of insulin-producing cells for the treatment of diabetes

Patients with diabetes experience decreased insulin secretion that is linked to a significant reduction in the number of islet cells. Reversal of diabetes can be achieved through islet transplantation, but the scarcity of donor islets severely hinders wide application of this therapeutic modality. Toward that end, embryonic stem cells, adult tissue-residing progenitor cells, and regenerating native beta-cells may serve as sources of islet cell surrogates. Insulin-producing cells generated from stem or progenitor cells display subsets of native beta-cell attributes, indicating the need for further development of methods for differentiation to completely functional beta-cells. Pharmacological approaches aiming at stimulating the in vivo/ex vivo regeneration of beta-cells have also been proposed as a way of augmenting islet cell mass. We review the current state of the generation of insulin-producing cells from different sources with emphasis on embryonic stem cells and adult progenitor cells. Challenges for the clinical use of these sources are also discussed.

Generation and expansion of multipotent mesenchymal progenitor cells from cultured human pancreatic islets

Cellular models and culture conditions for in vitro expansion of insulin-producing cells represent a key element to develop cell therapy for diabetes. Initial evidence that human beta-cells could be expanded after undergoing a reversible epithelial-mesenchymal transition has been recently negated by genetic lineage tracing studies in mice. Here, we report that culturing human pancreatic islets in the presence of serum resulted in the emergence of a population of nestin-positive cells. These proliferating cells were mainly C-peptide negative, although in the first week in culture, proliferating cells, insulin promoter factor-1 (Ipf-1) positive, were observed. Later passages of islet-derived cells were Ipf-1 negative and displayed a mesenchymal phenotype. These human pancreatic islet-derived mesenchymal (hPIDM) cells were expanded up to 10(14) cells and were able to differentiate toward adipocytes, osteocytes and chondrocytes, similarly to mesenchymal stem/precursor cells. Interestingly, however, under serum-free conditions, hPIDM cells lost the mesenchymal phenotype, formed islet-like clusters (ILCs) and were able to produce and secrete insulin. These data suggest that, although these cells are likely to result from preexisting mesenchymal cells rather than beta-cells, hPIDM cells represent a valuable model for further developments toward future replacement therapy in diabetes.

Directed differentiation of human embryonic stem cells towards a pancreatic cell fate

AIMS/HYPOTHESIS

The relative lack of successful pancreatic differentiation of human embryonic stem cells (hESCs) may suggest that directed differentiation of hESCs into definitive endoderm and subsequent commitment towards a pancreatic fate are not readily achieved. The aim of this study was to investigate whether sequential exposure of hESCs to epigenetic signals that mimic in vivo pancreatic development can efficiently generate pancreatic endodermal cells, and whether these cells can be further matured and reverse hyperglycaemia upon transplantation.

MATERIALS AND METHODS

The hESCs were sequentially treated with serum, activin and retinoic acid (RA) during embryoid body formation. The patterns of gene expression and protein production associated with embryonic germ layers and pancreatic endoderm were analysed by RT-PCR and immunostaining. The developmental competence and function of hESC-derived PDX1-positive cells were evaluated after in vivo transplantation.

RESULTS

Sequential treatment with serum, activin and RA highly upregulated the expression of the genes encoding forkhead box protein A2 (FOXA2), SRY-box containing gene 17 (SOX17), pancreatic and duodenal homeobox 1 (PDX1) and homeobox HB9 (HLXB9). The population of pancreatic endodermal cells that produced PDX1 was significantly increased at the expense of ectodermal differentiation, and a subset of the PDX1-positive cells also produced FOXA2, caudal-type homeobox transcription factor 2 (CDX2), and nestin (NES). After transplantation, the PDX1-positive cells further differentiated into mature cell types producing insulin and glucagon, resulting in amelioration of hyperglycaemia and weight loss in streptozotocin-treated diabetic mice.

CONCLUSIONS/INTERPRETATION

Our strategy allows the progressive differentiation of hESCs into pancreatic endoderm capable of generating mature pancreatic cell types that function in vivo. These findings may establish the basis of further investigations for the purification of transplantable islet progenitors derived from hESCs.

Glucagon-like peptide-1 differentiation of primate embryonic stem cells into insulin-producing cells

The present study was performed to determine whether glucagon-like peptide-1 (GLP-1) stimulates differentiation of nestin-selected embryonic stem cells into insulin-producing cells. Our experimental strategy began with the production of a highly enriched population of nestin-positive cells from embryoid bodies. These cells differentiated into insulin-producing cells after addition of GLP-1. Islet-like cell clusters (ICCs) formed in inducing culture. These nestin-positive cell-derived ICCs expressed numerous beta-cell lineage genes, including insulin; Glut-2; pancreatic duodenal homebox-1 protein (PDX-1); islet amyloid polypeptide (IAPP); neurogenin 3 (ngn3); and alpha, gamma, and delta cell gene markers. Cells of ICCs showed increased insulin protein expression, glucose-dependent insulin release, and coexpression of insulin and C-peptide. In addition, ICCs were characterized by coexpression of nestin/insulin and nestin/PDX-1. The levels of pancreas-related gene and protein expression and insulin secretion in the GLP-1 group were stronger than those in the normal controls. GLP-1 has been shown to be involved in stimulating the signaling pathways downstream of the transcription factor PDX-1, by increasing its protein and messenger RNA levels. In vivo, ICCs displayed the ability to reverse hyperglycemia in diabetic severe combined immunodeficiency (SCID) mice. We concluded that GLP-1 induced differentiation of nestin-positive progenitor embryonic stem cells into insulin-producing cells, which was achieved by upregulation of PDX-1 expression. This method may have future applications in stem cell therapy of diabetes.

Presence of endocrine and exocrine markers in EGFP-positive cells from the developing pancreas of a nestin/EGFP mouse

In order to purify and characterize nestin-positive cells in the developing pancreas a transgenic mouse was generated, in which the enhanced green fluorescent protein (EGFP) was driven by the nestin second intronic enhancer and upstream promoter. In keeping with previous studies on the distribution of nestin, EGFP was expressed in the developing embryo in neurones in the brain, eye, spinal cord, tail bud and glial cells in the small intestine. In the pancreas there was no detectable EGFP at embryonic day 11.5 (E11.5). EGFP expression appeared at E12.5 and increased in intensity through E14.5, E18.5 and post-natal day 1. Flow cytometry was used to quantify and purify the EGFP positive population in the E15.5 pancreas. The purified (96%) EGFP-expressing cells, which represent 20% of the total cell population, were shown by RT/PCR to express exocrine cell markers (amylase and P48) and endocrine cell markers (insulin 1, insulin 2, and Ngn3). They also expressed, at a lower level, PDX-1, Isl-1, and the islet hormones pancreatic polypeptide, glucagon and somatostatin as well as GLUT2, the stem cell marker ABCG2 and PECAM, a marker of endothelial cells. It was further shown by immunocytochemistry of the E15.5 pancreas that EGFP colocalised in separate subpopulations of cells that expressed nestin, insulin and amylase. These results support the conclusion that nestin expressing cells can give rise to both endocrine and exocrine cells. The ability to purify these putative progenitor cells may provide further insights into their properties and function.

Concise review: recent advances on the significance of stem cells in tissue regeneration and cancer therapies

In this study, we report on recent advances on the functions of embryonic, fetal, and adult stem cell progenitors for tissue regeneration and cancer therapies. We describe new procedures for derivation and maturation of these stem cells into the tissue-specific cell progenitors. The localization of the adult stem cells and their niches, as well as their implication in the tissue repair after injuries and during cancer progression, are also described. The emphasis is on the interactions among certain developmental signaling factors, such as hormones, epidermal growth factor, hedgehog, Wnt/beta-catenin, and Notch. These factors and their pathways are involved in the stringent regulation of the self-renewal and/or differentiation of adult stem cells. Novel strategies for the treatment of both diverse degenerating disorders, by cell replacement, and some metastatic cancer types, by molecular targeting multiple tumorigenic signaling elements in cancer progenitor cells, are also illustrated.

Multipotential nestin and Isl-1 positive mesenchymal stem cells isolated from human pancreatic islets

Mesenchymal cells in the developing pancreas express the neural stem cell marker nestin and the transcription factor islet-1 (Isl-1). Using defined culture conditions we isolated on a single cell basis nestin producing cells from human pancreatic islets. These cells were immortalized with lentiviral vectors coding for telomerase and mBmi. They are positive for Isl-1 and nestin and have the potential to adopt a pancreatic endocrine phenotype with expression of critical transcription factors including Ipf-1, Isl-1, Ngn-3, Pax4, Pax6, Nkx2.2, and Nkx6.1 as well as the islet hormones insulin, glucagon, and somatostatin. In addition, they can be differentiated into human albumin producing cells in vivo when grafted into a SCID mouse liver. In accordance with a mesenchymal phenotype, the cells were also able to adopt adipocytic or osteocytic phenotypes in vitro. In conclusion, cultured pancreatic islets contain nestin and Isl-1 positive mesenchymal stem cells with multipotential developmental capacity.

Glucagon-like peptide-1 receptor and proglucagon expression in mouse skin

Glucagon-like peptide-1 (GLP-1) is an insulinotropic hormone expressed by alternative post-translational processing of proglucagon in the intestines, endocrine pancreas, and brain. The multiple antidiabetogenic actions of GLP-1 include stimulation of the proliferation and differentiation of the insulin-producing beta cells in the pancreas. The GLP-1 receptor is widely distributed and has been identified in the endocrine pancreas, intestinal tract, brain, lung, kidney, and heart. Here we report the expression of the GLP-1 receptor and proglucagon in the skin of newborn mice located predominantly in the hair follicles, as well as in cultures of skin-derived cells that also express nestin, a marker of cultured cells that have dedifferentiated by epithelial to mesenchymal transition. In cultured skin cells, GLP-1 activates the MAPK/ERK signal transduction pathway, associated with cellular proliferation, differentiation, and cytoprotection. No evidence was found for the activation of cAMP or Ca2+ signaling pathways. Further, redifferentiation of cultured skin-derived cells by incubation in differentiation medium containing GLP-1 induced expression of the proinsulin-derived peptide, C-peptide. These findings suggest a possible paracrine/autocrine role for GLP-1 and its receptor in skin development and possibly also in folliculogenesis.

Isolation and in vitro characterization of pancreatic progenitor cells from the islets of diabetic monkey models

Recent studies on the identification of stem/progenitor cells within adult mouse and human pancreatic islets have raised the possibility that autologous transplantation might be used in treating type 1 diabetes. However, it is not yet known whether such stem/progenitor cells are impaired in type 1 diabetic patients or diabetic animal models. The latter would also allow us to test the efficacy of autologous transplantation in large animal models prior to clinical applications. The present study aims to determine the existence of stem/progenitor cells in the islets of diabetic monkey models and to assess the proliferation and differentiation potential of such cells in vitro. Our results indicate that there are pancreatic progenitor cells in the adult pancreatic islets in both normal and type 1 diabetic monkeys. The isolated pancreatic progenitor cells can be greatly expanded in culture. Upon the removal of growth medium, these cells spontaneously form islet-like cell clusters, which could be further induced to secrete insulin by inductive factors. Furthermore, the secretion of insulin and C-peptide from the islet-like cell clusters responds to glucose and other stimuli, indicating that the differentiated cells not only resemble beta-cells but also possess the unique biological function of beta-cells. This study provides a foundation for further characterization of adult pancreatic progenitor cells and autologous transplantation using pancreatic progenitor cells in treating diabetic monkeys.

NestinnegCD24low/- population from fetal Nestin-EGFP transgenic mice enriches the pancreatic endocrine progenitor cells

OBJECTIVES

To identify whether Nestin-positve cells or Nestin-negative cells in pancreas enrich potential pancreatic stem/progenitor cells.

METHODS

We generated transgenic mice carrying enhanced green fluorescent protein (EGFP) under the control of the nestin second-intronic enhancer and subsequently divided their embryonic pancreatic cells into different subpopulations according to the expression of EGFP and CD24 and characterized these subpopulations by in vitro culture.

RESULTS

The EGFP expression correlated well with that of endogenous Nestin. Only the NestinCD24 subpopulation was able to proliferate and generate immature islet-like cell clusters in long-term culture. Immature islet-like cell clusters could be induced to differentiate into insulin-, glucagon-, and somatostatin-positive cells.

CONCLUSIONS

Pancreatic endocrine stem/progenitor cells are enriched in the NestinCD24 population of embryonic pancreas.

Monoclonal side population progenitors isolated from human fetal pancreas

The side population (SP) phenotype might represent a common molecular feature for a wide variety of stem cells. The aim of this study was to investigate whether monoclonal SP progenitor cells were established from human fetal pancreas. Islet-like cell clusters (ICCs) were isolated from human fetal pancreas. Monolayer epithelium-like cells were obtained from the ICCs and passaged thereafter. Single SP or non-SP cells were sorted from these cells at the sixth passage. The rate of clone formation was about 2.7% for the SP cells, whereas there was no clone formation for the non-SP cells. The SP cell clones were further expanded for more than 15 passages and induced for differentiation into cells with characteristics of pancreatic beta-cells. We show for the first time that the monoclonal SP progenitors are established from human fetal pancreas. Therefore, this study may offer a novel method to purify pancreatic progenitor cells from human tissues.

Characterization of ABC transporter ABCB1 expressed in human neural stem/progenitor cells

We investigated the localization and functional expression of the ABC transporter ABCB1 in human fetal neural stem/progenitor cells (hNSPCs). RT-PCR analysis revealed ABCB1 gene expression in hNSPCs. We found a single band in immunoblotted hNSPCs lysates probed with ABCB1 antibody, and detected ABCB1 at the hNSPCs cell membrane by immunocytochemistry and subcellular fractionation. ABCB1 inhibitors and substrate, and ATP-depleting agents enhanced hNSPCs' rhodamine 123 accumulation, and hNSPCs microsomes had vanadate-sensitive ATPase activity. ABCB1 and nestin expression decreased during hNSPCs differentiation, while the astroglial marker GFAP increased. ABCB1 may maintain hNSPCs in an undifferentiated state and could be a neural stem/progenitor marker.

Nestin-positive progenitor cells isolated from human fetal pancreas have phenotypic markers identical to mesenchymal stem cells

AIM: To isolate nestin-positive progenitor cells from human fetal pancreas and to detect their surface markers and their capability of proliferation and differentiation into pancreatic islet endocrine cells in vitro.

METHODS: Islet-like cell clusters (ICCs) were isolated from human fetal pancreas by using collagenase digestion. The free-floating ICCs were handpicked and cultured in a new dish. After the ICCs developed into monolayer epithelium-like cells, they were passaged and induced for differentiation. Reverse transcription polymerase chain reaction (RT-PCR), immunofluorescence stain, fluorescence-activated cell sorting (FACS) and radioimmunoassay (RIA) were used to detect the expression of cell markers.

RESULTS: (1) The monolayer epithelium-like cells had highly proliferative potential and could be passaged more than 16 times in vitro; (2) RT-PCR analysis and immunofluorescence stain showed that these cells expressed both nestin and ABCG2, two of stem cell markers; (3) FACS analysis revealed that CD44, CD90 and CD147 were positive, whereas CD34, CD38, CD45, CD71, CD117, CD133 and HLA-DR were negative on the nestin-positive cells; (4) RT-PCR analysis showed that the mRNA expression of insulin, glucagon and pancreatic-duodenal homeobox gene-1 was detected, whereas the expression of nestin and neurogenin 3 disappeared in these cells treated with serum-free media supplemented with the cocktail of growth factors. Furthermore, the intra-cellular insulin content was detected by RIA after the induction culture.

CONCLUSION: Nestin-positive cells isolated from human fetal pancreas possess the characteristics of pancreatic progenitor cells since they have highly proliferative potential and the capability of differentiation into insulin-producing cells in vitro. Interestingly, the nestin-positive pancreatic progenitor cells share many phenotypic markers with mesenchymal stem cells derived from bone marrow.

A perspective on pancreatic stem/progenitor cells

The prevalence of both type 1 and type 2 diabetes mellitus is increasing throughout the world along with the ensuant morbidity and early mortality because of premature microvascular and macrovascular disease. Current insulin and drug therapies control diabetes, but do not cure it. Cell-based therapies offer the possibilities of a permanent cure for diabetes. Recently, success in the transplantation of pancreatic islets in the livers of type 1 diabetics has afforded the opportunity for a potential cure. However, the severe shortage of donor islets for transplantation limits the usefulness of this therapy. One approach is to exploit the use of stem cells, either embryo-derived or adult tissue-derived, as substrates to create islet tissue suitable for transplantation. Cells isolated from embryo blastocysts and from adult pancreas, liver, and bone marrow can be expanded extensively in vitro and differentiated into islet-like clusters that produce insulin, and, in some instances, can achieve glycemic control when transplanted into streptozotocin-induced diabetic mice. It is, now, also possible to envision the direct systemic administration of stem cells that would home in on and regenerate injured islets, or to administer stem cell stimulators that would enhance endogenous pancreatic stem cells to expand and differentiate into functional, insulin-producing beta-cells. This perspective discusses the potential applications of cellular medicines, in the new discipline of regenerative medicine, to achieve a cure for diabetes.

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Expression of stem cell markers and transcription factors during the remodeling of the rat pancreas after duct ligation

Ligation of the pancreatic duct has been shown to induce islet cell neogenesis from duct cells in the adult rat pancreas. The transcription factors that regulate islet cell neogenesis and the phenotype of putative precursor cells involved in neogenesis are unknown. We, therefore, studied the expression of the transcription factors Pdx1, Pbx1, Meis2, Nkx2.2 and the putative stem cell markers c-Kit and nestin in rat pancreata 3, 5 and 7 days after duct ligation. Immunocytochemical staining revealed a subpopulation of cells in the ligated portion of the pancreas that was positive for the putative stem cell markers c-Kit and nestin. The c-Kit immunoreactivity was upregulated, reaching a peak at day 3, while nestin expression peaked at day 7. The c-Kit-positive cells were located among the duct and islet cells, while nestin-expressing cells were found scattered in the duct epithelium at day 3 and around the ducts at day 7. Both c-Kit- and nestin-positive cells showed high proliferative activity, as determined by BrdU labeling. Pdx1 and Nkx2.2 were found predominantly in the duct cells of the ligated pancreas. There were significant changes in the expression patterns of Pbx1 and Meis2 in the ductular complexes. The findings indicate that the stem cell markers c-Kit and nestin as well as the transcription factors Pdx1 and Nkx2.2 are upregulated in compartments of the pancreas that are involved in islet cell neogenesis after duct ligation.

Characterization of c-Kit and nestin expression during islet cell development in the prenatal and postnatal rat pancreas

It has been well documented that there are abundant endocrine progenitor cells in the neonatal pancreas. However, little is known of their relative proportions or even their phenotypes. The aim of this study was to examine the normal distribution and characteristics of putative endocrine precursor cells, identified by c-Kit or nestin expression, within the prenatal and postnatal rat pancreas during islet cell development. Here, we provide evidence of the existence of a subset of ductal, islet, and acinar cells with an immature morphology and high proliferative capacity that expressed c-Kit or nestin. The proportion of islet cells expressing c-Kit or nestin was highest at embryonic day 18 (25 +/- 4% and 28 +/- 6%) and decreased significantly by postnatal day 28 (P < 0.01), 1.3 +/- 0.2% and 5.7 +/- 1%, respectively. The expression of nestin mRNA decreased throughout development, while c-Kit mRNA expression was found to slightly increase in the developing pancreas. Coexpression patterns indicated that c-Kit and nestin form two distinct cell populations in the postnatal pancreas, and infrequently coexpress with other pancreatic cell-specific markers. Furthermore, decreased c-Kit and nestin expression in the islets in postnatal life correlated with an increase in cells immunopositive for Pdx-1 compared with birth (36 +/- 5% vs. 60 +/- 3%, P < 0.01), which accompanied a doubling in the proportion of Glut-2-positive cells (39.4 +/- 4% vs. 68.8 +/- 3%, P < 0.01), both of which are mature beta-cell markers. Taken together, these findings suggest that c-Kit- and nestin-expressing cells represent endocrine precursor cells that undergo marked changes in population dynamics during the transition from prenatal to postnatal pancreatic development in the rat. Characterization of the phenotype, relative abundance and location of these cells within the developing pancreas is an important step toward creating a strategy for isolating stem cell populations and modeling islet cell differentiation in vitro.

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