Pancreatic stem cells remain unresolved

Therapeutic Strategies for Pancreatic-Cancer-Related Type 2 Diabetes Centered around Natural Products

Pancreatic ductal adenocarcinoma (PDAC), a highly malignant neoplasm, is classified as one of the most severe and devastating types of cancer. PDAC is a notable malignancy that exhibits a discouraging prognosis and a rising occurrence. The interplay between diabetes and pancreatic cancer exhibits a reciprocal causation. The identified metabolic disorder has been observed to possess noteworthy consequences on health outcomes, resulting in elevated rates of morbidity. The principal mechanisms involve the suppression of the immune system, the activation of pancreatic stellate cells (PSCs), and the onset of systemic metabolic disease caused by dysfunction of the islets. From this point forward, it is important to recognize that pancreatic-cancer-related diabetes (PCRD) has the ability to increase the likelihood of developing pancreatic cancer. This highlights the complex relationship that exists between these two physiological states. Therefore, we investigated into the complex domain of PSCs, elucidating their intricate signaling pathways and the profound influence of chemokines on their behavior and final outcome. In order to surmount the obstacle of drug resistance and eliminate PDAC, researchers have undertaken extensive efforts to explore and cultivate novel natural compounds of the next generation. Additional investigation is necessary in order to comprehensively comprehend the effect of PCRD-mediated apoptosis on the progression and onset of PDAC through the utilization of natural compounds. This study aims to examine the potential anticancer properties of natural compounds in individuals with diabetes who are undergoing chemotherapy, targeted therapy, or immunotherapy. It is anticipated that these compounds will exhibit increased potency and possess enhanced pharmacological benefits. According to our research findings, it is indicated that naturally derived chemical compounds hold potential in the development of PDAC therapies that are both safe and efficacious.

A postnatal network of co-hepato/pancreatic stem/progenitors in the biliary trees of pigs and humans

A network of co-hepato/pancreatic stem/progenitors exists in pigs and humans in Brunner's Glands in the submucosa of the duodenum, in peribiliary glands (PBGs) of intrahepatic and extrahepatic biliary trees, and in pancreatic duct glands (PDGs) of intrapancreatic biliary trees, collectively supporting hepatic and pancreatic regeneration postnatally. The network is found in humans postnatally throughout life and, so far, has been demonstrated in pigs postnatally at least through to young adulthood. These stem/progenitors in vivo in pigs are in highest numbers in Brunner's Glands and in PDGs nearest the duodenum, and in humans are in Brunner's Glands and in PBGs in the hepato/pancreatic common duct, a duct missing postnatally in pigs. Elsewhere in PDGs in pigs and in all PDGs in humans are only committed unipotent or bipotent progenitors. Stem/progenitors have genetic signatures in liver/pancreas-related RNA-seq data based on correlation, hierarchical clustering, differential gene expression and principal component analyses (PCA). Gene expression includes representative traits of pluripotency genes (SOX2, OCT4), endodermal transcription factors (e.g. SOX9, SOX17, PDX1), other stem cell traits (e.g. NCAM, CD44, sodium iodide symporter or NIS), and proliferation biomarkers (Ki67). Hepato/pancreatic multipotentiality was demonstrated by the stem/progenitors' responses under distinct ex vivo conditions or in vivo when patch grafted as organoids onto the liver versus the pancreas. Therefore, pigs are logical hosts for translational/preclinical studies for cell therapies with these stem/progenitors for hepatic and pancreatic dysfunctions.

Acinar cells and the development of pancreatic fibrosis

Pancreatic fibrosis is caused by excessive deposition of extracellular matrixes of collagen and fibronectin in the pancreatic tissue as a result of repeated injury often seen in patients with chronic pancreatic diseases. The most common causative conditions include inborn errors of metabolism, chemical toxicity and autoimmune disorders. Its pathophysiology is highly complex, including acinar cell injury, acinar stress response, duct dysfunction, pancreatic stellate cell activation, and persistent inflammatory response. However, the specific mechanism remains to be fully clarified. Although the current therapeutic strategies targeting pancreatic stellate cells show good efficacy in cell culture and animal models, they are not satisfactory in the clinic. Without effective intervention, pancreatic fibrosis can promote the transformation from pancreatitis to pancreatic cancer, one of the most lethal malignancies. In the normal pancreas, the acinar component accounts for 82% of the exocrine tissue. Abnormal acinar cells may activate pancreatic stellate cells directly as cellular source of fibrosis or indirectly via releasing various substances and initiate pancreatic fibrosis. A comprehensive understanding of the role of acinar cells in pancreatic fibrosis is critical for designing effective intervention strategies. In this review, we focus on the role of and mechanisms underlying pancreatic acinar injury in pancreatic fibrosis and their potential clinical significance.

Preclinical Research of Stem Cells: Challenges and Progress

In recent years, great breakthroughs have been made in basic research and clinical applications of stem cells in regenerative medicine and other fields, which continue to inspire people to explore the field of stem cells. With nearly unlimited self-renewal ability, stem cells can generate at least one type of highly differentiated daughter cell, which provides broad development prospects for the treatment of human organ damage and other diseases. In the field of stem cell research, related technologies for inducing or isolating stem cells are relatively mature, and a variety of stable stem cell lines have been successfully constructed. To realize the full clinical application of stem cells as soon as possible, it is more and more important to further optimize each stage of stem cell research while conforming to Current Good Manufacture Practices (cGMP) standards. Here, we synthesized recent developments in stem cell research and focus on the introduction of xenogenicity in the preclinical research process and the remaining problems of various cell bioreactors. Our goal is to promote the development of technologies for xeno-free culture and clinical expansion of stem cells through in-depth discussion of current research. This review will provide new insight into stem cell research protocols and will contribute to the creation of efficient and stable stem cell expansion systems.

Recent advances in tissue stem cells

Stem cells are undifferentiated cells capable of self-renewal and differentiation, giving rise to specialized functional cells. Stem cells are of pivotal importance for organ and tissue development, homeostasis, and injury and disease repair. Tissue-specific stem cells are a rare population residing in specific tissues and present powerful potential for regeneration when required. They are usually named based on the resident tissue, such as hematopoietic stem cells and germline stem cells. This review discusses the recent advances in stem cells of various tissues, including neural stem cells, muscle stem cells, liver progenitors, pancreatic islet stem/progenitor cells, intestinal stem cells, and prostate stem cells, and the future perspectives for tissue stem cell research.

Semi-modified okara whey diet increased insulin secretion in diabetic rats fed a basal or high fat diet

Lifestyle and diet preferences are primarily responsible for developing type 2 diabetes. In this study, okara was manufactured into okara whey crackers (OWC) to investigate its dietary role in controlling diabetes in streptozotocin-diabetic rats with and without a high-fat diet. Forty-eight rats were divided into eight groups. G1-G4 were nondiabetic and fed a basal diet, a basal diet with 30% crackers, high fat diet, and a high-fat diet with 30% crackers, respectively. G5-G8 were diabetic groups that received similar diets as previous groups. Blood glucose, liver function, lipid pattern, pancreas and liver histopathology, and insulin immunohistochemistry were performed. OWC improved measured parameters and histopathology of the liver and pancreas in diabetic rats. The area % of positive insulin cells was increased in G6 (5.20%) and G8 rats (2.83%) fed OWC compared to diabetic rats (1.17%). In conclusion, the use of 30% OWC in a semi-modified diet has controlled the hyperglycemia and hyperlipidemia associated with diabetes.

Long-Term Expansion of Pancreatic Islet Organoids from Resident Procr+ Progenitors

It has generally proven challenging to produce functional β cells in vitro. Here, we describe a previously unidentified protein C receptor positive (Procr⁺) cell population in adult mouse pancreas through single-cell RNA sequencing (scRNA-seq). The cells reside in islets, do not express differentiation markers, and feature epithelial-to-mesenchymal transition characteristics. By genetic lineage tracing, Procr⁺ islet cells undergo clonal expansion and generate all four endocrine cell types during adult homeostasis. Sorted Procr⁺ cells, representing ∼1% of islet cells, can robustly form islet-like organoids when cultured at clonal density. Exponential expansion can be maintained over long periods by serial passaging, while differentiation can be induced at any time point in culture. β cells dominate in differentiated islet organoids, while α, δ, and PP cells occur at lower frequencies. The organoids are glucose-responsive and insulin-secreting. Upon transplantation in diabetic mice, these organoids reverse disease. These findings demonstrate that the adult mouse pancreatic islet contains a population of Procr⁺ endocrine progenitors.

Stem Cell Therapy for Diabetes: Beta Cells versus Pancreatic Progenitors

Diabetes mellitus (DM) is one of the most prevalent metabolic disorders. In order to replace the function of the destroyed pancreatic beta cells in diabetes, islet transplantation is the most widely practiced treatment. However, it has several limitations. As an alternative approach, human pluripotent stem cells (hPSCs) can provide an unlimited source of pancreatic cells that have the ability to secrete insulin in response to a high blood glucose level. However, the determination of the appropriate pancreatic lineage candidate for the purpose of cell therapy for the treatment of diabetes is still debated. While hPSC-derived beta cells are perceived as the ultimate candidate, their efficiency needs further improvement in order to obtain a sufficient number of glucose responsive beta cells for transplantation therapy. On the other hand, hPSC-derived pancreatic progenitors can be efficiently generated in vitro and can further mature into glucose responsive beta cells in vivo after transplantation. Herein, we discuss the advantages and predicted challenges associated with the use of each of the two pancreatic lineage products for diabetes cell therapy. Furthermore, we address the co-generation of functionally relevant islet cell subpopulations and structural properties contributing to the glucose responsiveness of beta cells, as well as the available encapsulation technology for these cells.

Long-Term Liraglutide Administration Induces Pancreas Neogenesis in Adult T2DM Mice

In vivo beta-cell neogenesis may be one way to treat diabetes. We aimed to investigate the effect of glucagon-like peptide-1 (GLP-1) on beta-cell neogenesis in type 2 diabetes mellitus (T2DM). Male C57BL/6J mice, 6 wk old, were randomly divided into three groups: Control, T2DM, and T2DM + Lira. T2DM was induced using high-fat diet and intraperitoneal injection of streptozotocin (40 mg/kg/d for 3 d). At 8 wk after streptozotocin injection, T2DM + Lira group was injected intraperitoneally with GLP-1 analog liraglutide (0.8 mg/kg/d) for 4 wk. Apparently for the first time, we report the appearance of a primitive bud connected to pancreas in all adult mice from each group. The primitive bud was characterized by scattered single monohormonal cells expressing insulin, GLP-1, somatostatin, or pancreatic polypeptide, and four-hormonal cells, but no acinar cells and ductal epithelial cells. Monohormonal cells in it were small, newborn, immature cells that rapidly proliferated and expressed cell markers indicative of immaturity. In parallel, Ngn3+ endocrine progenitors and Nestin+ cells existed in the primitive bud. Liraglutide facilitated neogenesis and rapid growth of acinar cells, pancreatic ducts, and blood vessels in the primitive bud. Meanwhile, scattered hormonal cells aggregated into cell clusters and grew into larger islets; polyhormonal cells differentiated into monohormonal cells. Extensive growth of exocrine and endocrine glands resulted in the neogenesis of immature pancreatic lobes in adult mice of T2DM + Lira group. Contrary to predominant acinar cells in mature pancreatic lobes, there were still a substantial number of mesenchymal cells around acinar cells in immature pancreatic lobes, which resulted in the loose appearance. Our results suggest that adult mice preserve the capacity of pancreatic neogenesis from the primitive bud, which liraglutide facilitates in adult T2DM mice. To our knowledge, this is the first time such a phenomenon has been reported.

Salivary Gland Stem Cells and Tissue Regeneration: An Update on Possible Therapeutic Application

The aim of this review is to combine literature and experimental data concerning the impact of salivary gland (SG) stem cells (SCs) and their therapeutic prospects in tissue regeneration. So far, SCs were isolated from human and rodent major and minor SGs that enabled their regeneration. Several scaffolds were also combined with "SCs" and different "proteins" to achieve guided differentiation, although none have been proven as ideal. A new aspect of SC therapy aims to establish a vice versa relationship between SG and other ecto- or endodermal organs such as the pancreas, liver, kidneys, and thyroid. SC therapy could be a cheap and simple, non-traumatic, and individualized therapy for medically challenging cases like xerostomia and major organ failures. Functional improvement has been achieved in these organs, but till date, the whole organ in vivo regeneration was not achieved. Concerns about malignant formations and possible failures are yet to be resolved. In this review article, we highlight the basic embryology of SGs, existence of SG SCs with a detailed exploration of various cellular markers, scaffolds for tissue engineering, and, in the later part, cover potential therapeutic applications with a special focus on the pancreas and liver. Keywords: Salivary gland stem cells, Stem cell therapy, Tissue regeneration.

A periodic table of cell types

Single cell biology is currently revolutionizing developmental and evolutionary biology, revealing new cell types and states in an impressive range of biological systems. With the accumulation of data, however, the field is grappling with a central unanswered question: what exactly is a cell type? This question is further complicated by the inherently dynamic nature of developmental processes. In this Hypothesis article, we propose that a 'periodic table of cell types' can be used as a framework for distinguishing cell types from cell states, in which the periods and groups correspond to developmental trajectories and stages along differentiation, respectively. The different states of the same cell type are further analogous to 'isotopes'. We also highlight how the concept of a periodic table of cell types could be useful for predicting new cell types and states, and for recognizing relationships between cell types throughout development and evolution.

Exosomes, metastases, and the miracle of cancer stem cell markers

Cancer-initiating cells (CIC) are the driving force in tumor progression. There is strong evidence that CIC fulfill this task via exosomes (TEX), which modulate and reprogram stroma, nontransformed cells, and non-CIC. Characterization of CIC, besides others, builds on expression of CIC markers, many of which are known as metastasis-associated molecules. We here discuss that the linkage between CIC/CIC-TEX and metastasis-associated molecules is not fortuitously, but relies on the contribution of these markers to TEX biogenesis including loading and TEX target interactions. In addition, CIC markers contribute to TEX binding- and uptake-promoted activation of signaling cascades, transcription initiation, and translational control. Our point of view will be outlined for pancreas and colon CIC highly expressing CD44v6, Tspan8, EPCAM, claudin7, and LGR5, which distinctly but coordinately contribute to tumor progression. Despite overwhelming progress in unraveling the metastatic cascade and the multiple tasks taken over by CIC-TEX, there remains a considerable gap in linking CIC biomarkers, TEX, and TEX-initiated target modulation with metastasis. We will try to outline possible bridges, which could allow depicting pathways for new and expectedly powerful therapeutic interference with tumor progression.

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.

Relevance of Oxygen Concentration in Stem Cell Culture for Regenerative Medicine

The key hallmark of stem cells is their ability to self-renew while keeping a differentiation potential. Intrinsic and extrinsic cell factors may contribute to a decline in these stem cell properties, and this is of the most importance when culturing them. One of these factors is oxygen concentration, which has been closely linked to the maintenance of stemness. The widely used environmental 21% O₂ concentration represents a hyperoxic non-physiological condition, which can impair stem cell behaviour by many mechanisms. The goal of this review is to understand these mechanisms underlying the oxygen signalling pathways and their negatively-associated consequences. This may provide a rationale for culturing stem cells under physiological oxygen concentration for stem cell therapy success, in the field of tissue engineering and regenerative medicine.

Pancreatic resident endocrine progenitors demonstrate high islet neogenic fidelity and committed homing towards diabetic mice pancreas

Pancreatic progenitors have been explored for their profound characteristics and unique commitment to generate new functional islets in regenerative medicine. Pancreatic resident endocrine progenitors (PREPs) with mesenchymal stem cell (MSC) phenotype were purified from BALB/c mice pancreas and characterized. PREPs were differentiated into mature islet clusters in vitro by activin-A and swertisin and functionally characterized. A temporal gene and protein profiling was performed during differentiation. Furthermore, PREPs were labeled with green fluorescent protein (GFP) and transplanted intravenously into streptozotocin (STZ) diabetic mice while monitoring their homing and differentiation leading to amelioration in the diabetic condition. PREPs were positive for unique progenitor markers and transcription factors essential for endocrine pancreatic homeostasis along with having the multipotent MSC phenotype. These cells demonstrated high fidelity for islet neogenesis in minimum time (4 days) to generate mature functional islet clusters (shortest reported period for any isolated stem/progenitor). Furthermore, GFP-labeled PREPs transplanted in STZ diabetic mice migrated and localized within the injured pancreas without trapping in any other major organ and differentiated rapidly into insulin-producing cells without an external stimulus. A rapid decrease in fasting blood glucose levels toward normoglycemia along with significant increase in fasting serum insulin levels was observed, which ameliorated the diabetic condition. This study highlights the unique potential of PREPs to generate mature islets within the shortest period and their robust homing toward the damaged pancreas, which ameliorated the diabetic condition suggesting PREPs affinity toward their niche, which can be exploited and extended to other stem cell sources in diabetic therapeutics.

Evaluating KIND1 human embryonic stem cell-derived pancreatic progenitors to ameliorate streptozotocin-induced diabetes in mice

Background & objectives:

Diabetes is a global disease burden. Various stem cell types are being explored to serve as an alternative source of islets. This study was conducted to evaluate the ability of in-house developed human embryonic stem (hES) cells-derived pancreatic progenitors to ameliorate diabetic symptoms in mice.

Methods:

Pancreatic progenitors were packed in macro-capsules and transplanted into six male Swiss mice and four mice were taken as controls. Thirty days post-transplantation, diabetes was induced by streptozotocin treatment. Mice were then followed up for >100 days and body weight and blood glucose levels were regularly monitored.

Results:

Control mice lost weight, maintained high glucose levels and did not survive beyond 40 days, whereas transplanted group maintained body weight and four of the six mice had lowered blood glucose levels. About five-fold increase was observed in human C-peptide levels in the recipients of progenitor transplants as compared to diabetic control.

Interpretation & conclusions:

The beneficial effect of transplanted cells was not long-lasting. Further studies are required to critically evaluate and compare the potential of endogenous pluripotent stem cells and hES cells-derived progenitors before moving from bench to the bedside.

Stem cell-derived exosomes: a novel vector for tissue repair and diabetic therapy

Exosomes are extracellular vesicles (EVs) secreted from a majority of cell types. Exosomes play a role in healthy and pathogenic intercellular interactions via the transfer of proteins, lipids and RNA. The contents and effects of exosomes vary depending on the properties of the originating cell. Exosomes secreted from some cell types, including stem cells, carry biological factors implicated in the protection, regeneration and angiogenesis of damaged tissues. Due to these properties, exosomes have attracted attention as a novel vector for regenerative therapies. Exosomes as a therapeutic tool could have applications for the treatment of many disorders characterized by chronic tissue damage. Exosomes derived from stem cells could be applied to repair or prevent damage from the complications of diabetes mellitus. The immunomodulatory and reparative properties of stem cell-derived exosomes could protect or even restore an early-stage type 1 diabetic patient's original islets from autoimmune destruction. Exosomes could also possibly suppress graft rejection of pancreatic islet transplants. Therefore, it is our recommendation that the treatment of diabetes mellitus using exosome-based therapies be further explored. Development of novel therapies using exosomes is slowed by a limited understanding of their mechanisms. This hurdle must be overcome to pave the way for clinical trials and ultimately the adaptation of exosomes as a therapeutic vector.

Stem cells to replace or regenerate the diabetic pancreas: Huge potential & existing hurdles

Various stem cell sources are being explored to treat diabetes since the proof-of-concept for cell therapy was laid down by transplanting cadaveric islets as a part of Edmonton protocol in 2000. Human embryonic stem (hES) cells derived pancreatic progenitors have got US-FDA approval to be used in clinical trials to treat type 1 diabetes mellitus (T1DM). However, these progenitors more closely resemble their foetal counterparts and thus whether they will provide long-term regeneration of adult human pancreas remains to be demonstrated. In addition to lifestyle changes and administration of insulin sensitizers, regeneration of islets from endogenous pancreatic stem cells may benefit T2DM patients. The true identity of pancreatic stem cells, whether these exist or not, whether regeneration involves reduplication of existing islets or ductal epithelial cells transdifferentiate, remains a highly controversial area. We have recently demonstrated that a novel population of very small embryonic-like stem cells (VSELs) is involved during regeneration of adult mouse pancreas after partial-pancreatectomy. VSELs (pluripotent stem cells in adult organs) should be appreciated as an alternative for regenerative medicine as these are autologous (thus immune rejection issues do not exist) with no associated risk of teratoma formation. T2DM is a result of VSELs dysfunction with age and uncontrolled proliferation of VSELs possibly results in pancreatic cancer. Extensive brainstorming and financial support are required to exploit the potential of endogenous VSELs to regenerate the pancreas in a patient with diabetes.

Adult Murine Pancreatic Progenitors Require Epidermal Growth Factor and Nicotinamide for Self-Renewal and Differentiation in a Serum- and Conditioned Medium-Free Culture

Adult pancreatic stem and progenitor cells may serve as an alternative source of insulin-secreting endocrine cells in cell replacement therapy for type 1 diabetes, but much remained unknown about these cells. We previously identified adult murine pancreatic progenitor-like cells that displayed in vitro self-renewal and tri-lineage differentiation activities in a three-dimensional colony/organoid assay containing 1% methylcellulose and 5% Matrigel. However, the presence of other undefined culture components, such as serum and conditioned medium, has prevented a complete understanding of the signals required for progenitor cell growth. Here, we have established a serum-free, conditioned medium-free colony assay with the inclusion of seven defined factors: epidermal growth factor (EGF), R-Spondin 1 (RSPO1), Noggin, nicotinamide, exendin-4, activin B, and vascular endothelial growth factor (VEGF)-A. The requirements for colony growth were characterized and we found that EGF and nicotinamide were necessary and sufficient for the colony growth and long-term self-renewal of these progenitors. However, the seven factor (7F) culture medium better induced colony size and self-renewal in long-term culture than EGF plus nicotinamide alone. Individual 3-week-old colonies grown in the 7F culture medium expressed ductal, acinar, and endocrine lineage markers, suggesting that tri-lineage differentiation of the tri-potent progenitors was occurring without genetic manipulation. A delayed inhibition of Notch signaling using small molecules in 2-week-old cultures enhanced endocrine gene expression in 3-week-old colonies. This better-defined colony assay system will enable our and other laboratories for in-depth mechanistic studies on the biology of these progenitor cells.

De Novo Prediction of Stem Cell Identity using Single-Cell Transcriptome Data

Adult mitotic tissues like the intestine, skin, and blood undergo constant turnover throughout the life of an organism. Knowing the identity of the stem cell is crucial to understanding tissue homeostasis and its aberrations upon disease. Here we present a computational method for the derivation of a lineage tree from single-cell transcriptome data. By exploiting the tree topology and the transcriptome composition, we establish StemID, an algorithm for identifying stem cells among all detectable cell types within a population. We demonstrate that StemID recovers two known adult stem cell populations, Lgr5+ cells in the small intestine and hematopoietic stem cells in the bone marrow. We apply StemID to predict candidate multipotent cell populations in the human pancreas, a tissue with largely uncharacterized turnover dynamics. We hope that StemID will accelerate the search for novel stem cells by providing concrete markers for biological follow-up and validation.

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StemID infers the lineage tree and identifies stem cells from single-cell mRNA-seq data

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Direct links of stem cells to distinct sub-types reflect transcriptome plasticity

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The permissive stem cell transcriptome is characterized by high entropy

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StemID infers candidate multipotent cell populations in the human pancreas

Insulin-secreting β cells require a post-genomic concept

Pancreatic insulin-secreting β cells are essential in maintaining normal glucose homeostasis accomplished by highly specialized transcription of insulin gene, of which occupies up to 40% their transcriptome. Deficiency of these cells causes diabetes mellitus, a global public health problem. Although tremendous endeavors have been made to generate insulin-secreting cells from human pluripotent stem cells (i.e., primitive cells capable of giving rise to all cell types in the body), a regenerative therapy to diabetes has not yet been established. Furthermore, the nomenclature of β cells has become inconsistent, confusing and controversial due to the lack of standardized positive controls of developmental stage-matched in vivo cells. In order to minimize this negative impact and facilitate critical research in this field, a post-genomic concept of pancreatic β cells might be helpful. In this review article, we will briefly describe how β cells were discovered and islet lineage is developed that may help understand the cause of nomenclatural controversy, suggest a post-genomic definition and finally provide a conclusive remark on future research of this pivotal cell.

Identification of CD90 as Putative Cancer Stem Cell Marker and Therapeutic Target in Insulinomas

The long-term prognosis after surgical resection of malignant insulinoma (INS) is poor. Novel adjuvant therapies, specifically targeting cancer stem cells (CSCs), are warranted. Therefore, the goal of this study was to characterize and target putative INS CSCs. Using fluorescence-activated cell sorting, human INS cell line CM and pancreatic carcinoid cell line BON1 were screened for the presence of stem cell-associated markers. CD90, CD166, and GD2 were identified as potential CSC markers. Only CD90(+) INS cells had an increased tumor-initiating potential in athymic nude mice. Anti-CD90 monoclonal antibodies decreased the viability and metastatic potential of injected cells in a zebrafish embryo INS xenograft model. Primary INS stained positive for CD90 by immunohistochemistry, however also intratumoral fibroblasts and vascular endothelium showed positive staining. The results of this study suggest that anti-CD90 monoclonals form a potential novel adjuvant therapeutic modality by targeting either INS cells directly, or by targeting the INS microenvironment.

[Cellular therapy of diabetes: focus on the latest developments]

Islet transplantation has set the ground for diabetes cell therapy and is still undergoing various developments that might improve clinical outcomes. Alternative sources for β-cell replacement strategies are now led by human pluripotent stem cells that demonstrate near-normal β-cell features after in vitro differentiation and which can reverse diabetes in mice. Yet, their propensity for tumor formation is still unresolved. The adult pancreas is suggested as a reservoir of facultative progenitors that could represent adequate candidates for β-cell engineering, either in vivo through pharmacological treatment or after expansion in culture. This review focuses on the latest developments in protocols aiming at de novo production of functional β cells.

New Insights into Diabetes Cell Therapy

Since insulin discovery, islet transplantation was the first protocol to show the possibility to cure patients with type 1 diabetes using low-risk procedures. The scarcity of pancreas donors triggered a burst of studies focused on the production of new β cells in vitro. These were rapidly dominated by pluripotent stem cells (PSCs) demonstrating diabetes-reversal potential in diabetic mice. Subsequent enthusiasm fostered a clinical trial with immunoisolated embryonic-derived pancreatic progenitors. Yet safety is the Achilles' heel of PSCs, and a whole branch of β cell engineering medicine focuses on transdifferentiation of adult pancreatic cells. New data showed the possibility to chemically stimulate acinar or α cells to undergo β cell neogenesis and provide opportunities to intervene in situ without the need for a transplant, at least after weighing benefits against systemic adverse effects. The current studies suggested the pancreas as a reservoir of facultative progenitors (e.g., in the duct lining) could be exploited ex vivo for expansion and β cell differentiation in timely fashion and without the hurdles of PSC use. Diabetes cell therapy is thus a growing field not only with great potential but also with many pitfalls to overcome for becoming fully envisioned as a competitor to the current treatment standards.

Lineage Reprogramming: A Promising Road for Pancreatic β Cell Regeneration

Cell replacement therapy is a promising method to restore pancreatic β cell function and cure diabetes. Distantly related cells (fibroblasts, keratinocytes, and muscle cells) and developmentally related cells (hepatocytes, gastrointestinal, and pancreatic exocrine cells) have been successfully reprogrammed into β cells in vitro and in vivo. However, while some reprogrammed β cells bear similarities to bona fide β cells, others do not develop into fully functional β cells. Here we review various strategies currently used for β cell reprogramming, including ectopic expression of specific transcription factors associated with islet development, repression of maintenance factors of host cells, regulation of epigenetic modifications, and microenvironmental changes. Development of simple and efficient reprogramming methods is a key priority for developing fully functional β cells suitable for cell replacement therapy.

Salivary Glands: Stem Cells, Self-duplication, or Both?

Understanding the intrinsic potential for renewal and regeneration within a tissue is critical for the rational design of reparative strategies. Maintenance of the salivary glands is widely thought to depend on the differentiation of stem cells. However, there is also new evidence that homeostasis of the salivary glands, like that of the liver and pancreas, relies on self-renewal of differentiated cells rather than a stem cell pool. Here, we review the evidence for both modes of turnover and consider the implications for the process of regeneration. We propose that the view of salivary glands as postmitotic and dependent on stem cells for renewal be revised to reflect the proliferative activity of acinar cells and their role in salivary gland homeostasis.

Intricacies of Pluripotency

Pluripotent stem cells have the potential to differentiate into 200 odd cell types present in adult body. Pluripotent stem cells available for regenerative medicine include embryonic stem (ES) cells, induced pluripotent stem (iPS) cells and very small ES-like stem (VSELs) cells. Nuclear OCT-4 is one of the crucial factors that dictate pluripotent state. Compared to ES/iPS cells grown in Petri dish, VSELs exist in adult body organs and results are emerging to suggest that they may have better potential to regenerate adult organs. This is because of their distinct epigenetic status as they are closer to the primordial germ cells from the epiblast-stage embryo compared to inner cell mass from which ES cells are obtained in vitro. We need to make special efforts to study them as they are very small in size and tend to get lost during processing. VSELs exist in adult organs, get mobilized in response to stress, undergo asymmetric cell divisions to give rise to tissue specific progenitors which further differentiate into various cell types and are possibly better candidates for regenerative medicine because they have no associated risk of tumor formation or immunological rejection. They are possibly also the ‘embryonic remnants’ in adult organs responsible for initiating cancer. Thus, rather than not accepting VSELs because they neither form teratoma nor divide in vitro like ES cells, it is time that scientific community should think of revising the definition of the term ‘pluripotency’.

Very small embryonic-like stem cells are involved in pancreatic regeneration and their dysfunction with age may lead to diabetes and cancer

Mouse pancreas has a remarkable ability to regenerate after partial pancreatectomy, and several investigators have studied the underlying mechanisms involved in this regeneration process; however, the field remains contentious. Elegant lineage-tracing studies undertaken over a decade have generated strong evidence against neogenesis from stem cells and in favor of reduplication of pre-existing islets. Ductal epithelium has also been implicated during regeneration. We recently provided direct evidence for the possible involvement of very small embryonic-like stem cells (VSELs) during regeneration after partial pancreatectomy in mice. VSELs were first reported in pancreas in 2008 and are mobilized in large numbers after treating mice with streptozotocin and in patients with pancreatic cancer. VSELs can be detected in mouse pancreas as small-sized LIN⁻/CD45⁻/SCA-1⁺ cells (3 to 5 μm), present in small numbers (0.6%), which express nuclear Oct-4 (octamer-binding transcription factor 4) and other pluripotent markers along with their immediate descendant ‘progenitors’, which are slightly bigger and co-express Oct-4 and PDX-1. VSELs and the progenitors get mobilized in large numbers after partial pancreatectomy and regenerate both pancreatic islets and acinar cells. In this review, we deliberate upon possible reasons why VSELs have eluded scientists so far. Because of their small size, VSELs are probably unknowingly and inadvertently discarded during processing. Similar to menopause and related loss of ovarian function, type 2 diabetes mellitus occurs because of a decline in beta-cell function possibly resulting from an age-related compromised niche which does not allow VSELs to maintain normal homeostasis. As suggested earlier for ovarian cancers, the presence of Oct-4 and other pluripotent markers in pancreatic cancers is suggestive of VSELs as the possible cancer-initiating stem cells. Several issues raised in the review require urgent confirmation and thus provide scope for further research before arriving at a consensus on the fundamental role played by VSELs in normal pancreas biology and during regeneration, aging, and cancer. In the future, such understanding may allow manipulation of endogenous VSELs to our advantage in patients with diabetes and also to treat cancer.