Bio-engineering inslulin-secreting cells from embryonic stem cells: a review of progress

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.

Directed Differentiation of Mouse Embryonic Stem Cells into Pancreatic-Like or Neuronal- and Glial-Like Phenotypes

The derivation of definitive endoderm and in particular endocrine cell types from undifferentiated embryonic stem (ES) cells remains difficult to achieve. In this study, we investigated the potential to regulate the differentiation of ES cells into endodermal derivatives using extracellular factors previously associated with various aspects of pancreatic development. Feeder-free-cultured mouse ESD3 cells were manipulated to form embryoid bodies (EBs) in the presence of retinoic acid (RA). RA-treated EBs were subsequently exposed to sodium butyrate (SB), betacellulin (BTC) or activin A (AA). A comparative analysis was performed on these models of directed differentiation in parallel with a model of spontaneous differentiation. Lineage differentiation was determined by profiling multilineage marker transcript expression (neuronal, myogenic, exocrine and endocrine pancreas, extraembryonic and apoptotic) and subsequent protein expression within ES-derived cultures. Using a two-stage differentiation protocol developed during this study, we successfully demonstrated the derivation of an intermediate multipotential population (RA_EBs) from undifferentiated ES cells that preferentially gives rise to pancreatic endocrine insulin-expressing cell types in the presence of SB, and neuronal- and glial-like cell types in the presence of AA or BTC.

Insulin-producing cells from embryonic stem cells experimental considerations

The main objective of cell bioengineering is to generate customized tissues that allow recovering the lost functions in the organism in the absence of immune rejection. Although the possibility of in vitro generation of entire organs is technically very complex, obtaining specific cell types for replacement therapies seems to be a more realistic goal at mean time. In this context, those pathologies affected by the dysfunction of a specific cell type, as it is the case of beta-cell in diabetes, would be in principle candidates to benefit from cell transplantation protocols. Embryonic stem cells offer interesting possibilities in this context because they fulfill two important criteria: (i) High proliferation rate by symmetric cell division, overcoming the problem of biomass scarcity and (ii) Plasticity of differentiating to all cell types present in the adult organism, including the germ line. Different approaches have been developed in vitro to obtain insulin-producing cells from embryonic stem cells. Nevertheless, a definitive protocol does not exist yet. However, the experience accumulated in this field by the different laboratories has provided considering key points that would help to design a preferred protocol in the future.

Beta cells occur naturally in extrahepatic bile ducts of mice

Insulin-secreting beta cells were thought to reside only in the pancreas. Here, we show that beta cells are also present in the extra-hepatic bile ducts of mice. They are characterised by insulin and C-peptide content, the presence of secretory granules that are immunoreactive for insulin, and the ducts exhibit glucose-stimulated insulin secretion. Genetic lineage labelling shows that these beta cells arise from the liver domain rather than the pancreas and, by histological study, they appear to be formed directly from the bile duct epithelium in late embryogenesis. Other endocrine cell types (producing somatostatin and pancreatic polypeptide) are also found in close association with the bile-duct-derived beta cells, but exocrine pancreatic tissue is not present. This discovery of beta cells outside the mammalian pancreas has implications for regenerative medicine, indicating that biliary epithelium might offer a new source of beta cells for the treatment of diabetes. The finding also has evolutionary significance, because it is known that certain basal vertebrates usually form all of their beta cells from the bile ducts. The mammalian bile-duct-derived beta cells might therefore represent an extant trace of the evolutionary origin of the vertebrate beta cell.

Role of small bioorganic molecules in stem cell differentiation to insulin-producing cells

The use of small specific molecules has been instrumental in the modulation of stem cell proliferation and differentiation to obtain insulin-containing cells. Examples include nutrients (glucose, nicotinamide and retinoic acid), acids (butyrate), alkaloids (cyclopamine and conophylline) and pharmacological agents (LY294002 and wortmannin). These molecules, alone or in combination with specific growth factors and hormones, will likely provide key information to design specific culture media in order to obtain customized cells for implantation in diabetes. In addition, the study of such molecules will help to understand the mechanisms involved in stem cell biology as well as contribute to the design of specific drugs for islet repair and regeneration in diabetes.

Propagation and maintenance of undifferentiated human embryonic stem cells

Human embryonic stem (hES) cells, like other stem cells, have the capacity to self-renew without differentiation. Although hES cells can be differentiated to many different tissue types in vitro, clinical uses have not yet been realized from the study of hES cells. Anticipation that these cells would be immediately useful for creating models of human disease has not yet been fulfilled. However, because of their self-renewing and pluripotential nature, hES cells indeed hold unique promise for many areas of research and medicine. A major problem complicating developments in hES cell research is the difficulty of propagating and maintaining these cells in vitro without differentiation. This review addresses this problem and potential solutions in detail. In addition, the current state of research regarding the growth and maintenance of hES cells is summarized, along with basic protocols utilized by our laboratory for the successful propagation, characterization, and investigation of hES cells.

Insulin-secreting cells derived from stem cells: clinical perspectives, hypes and hopes

Diabetes is a degenerative disease that results from the selective destruction of pancreatic beta-cells. These cells are responsible for insulin production and secretion in response to increases in circulating concentrations of nutrients, such as glucose, fatty acids and amino acids. This degenerative disease can be treated by the transplantation of differentiated islets obtained from cadaveric donors, according to a new surgical intervention developed as Edmonton protocol. Compared to the classical double transplant kidney-pancreas, this new protocol presents several advantages, concerning to the nature of the implant, immunosuppressive drug regime and the surgical procedure itself. However, the main problem to face in any islet transplantation program is the scarcity of donor pancreases and the low yield of islets isolated (very often around 50%) from each pancreas. Nevertheless, transplanted patients presented no adverse effects and no progression of diabetic complications. In the search of new cell sources for replacement trials, stem cells from embryonic and adult origins represent a key alternative. In order to become a realistic clinical issue transplantation of insulin-producing cells derived from stem cells, it needs to overcome multiple experimental obstacles. The first one is to develop a protocol that may allow obtaining a pure population of functional insulin-secreting cells as close as possible to the pancreatic beta-cell. The second problem should concern to the transplantation itself, considering issues related to immune rejection, tumour formation, site for implant, implant survival, and biosafety mechanisms. Although transplantation of bioengineered cells is still far in time, experience accumulated in islet transplantation protocols and in experiments with appropriate animal models will give more likely the clues to address this question in the future.

Ectodermal commitment of insulin‐producing cells derived from mouse embryonic stem cells

Embryonic stem cells possess the ability to differentiate in vitro into a variety of cell lineages, including insulin-producing cells. Pancreatic beta-cells derive from foregut endoderm during embryonic development. However, previous reports using transgenic mice strongly indicate that insulin-positive cells may be generated also through the neuroectoderm pathway. To analyze this point, a culture system was performed in which only ectoderm committed cells were present. Based on published work, we achieved this by maintaining transfected clonal R1 mouse embryonic stem cells in monolayer in the absence of LIF. Contrary to differentiation protocols via embryoid body formation, monolayer cultured cells displayed ectodermal fates according to the marker gene expression pattern. Under these particular conditions, neomycin was added in order to select insulin-expressing cells. The cell lineage obtained expressed Pdx1, Pax6, Isl1, AChE, MBP, TH, and GS genes, confirming ectodermal commitment, even though some of these factors are also expressed in endoderm. In addition these cells displayed excitatory properties similar to astrocytes. Co-expression of insulin II and nestin was observed in monolayer culture and in the presence of specific conditioned media. No expression of early endodermal markers was detected along monolayer cultures. Altogether, these observations suggest that cells with ectoderm fates could participate in vitro in the derivation of insulin-producing cells. These results have implications for insulin gene regulation and hormone secretion in order to generate insulin-producing cells for replacement protocols in the treatment of diabetes.

Therapeutic insulins and their large-scale manufacture

Biotechnological innovations over the past 25 years have underpinned the rapid development of a thriving biopharmaceutical sector. Therapeutic insulin remains one of the most commonly used products of pharmaceutical biotechnology and insulin-based products command annual global sales in excess of $4.5 billion. Innovations in its method of production and in particular the advent of engineered insulin analogues provide a fascinating insight into how scientific and technological advances have impacted upon the pharmaceutical biotechnology sector as a whole. Current insulin-based diabetes research is increasingly focused not on the insulin molecule per se, but upon areas such as the development of non-parenteral insulin delivery systems, as well as organ-/cell-based and gene therapy-based approaches to controlling the disease.

Redox-mediated enrichment of self-renewing adult human pancreatic cells that possess endocrine differentiation potential

OBJECTIVES

The limited availability of transplantable human islets has stimulated the development of methods needed to isolate adult pancreatic stem/progenitor cells capable of self-renewal and endocrine differentiation. The objective of this study was to determine whether modulation of intracellular redox state with N-acetyl-L-cysteine (NAC) would allow for the propagation of pancreatic stem/progenitor cells from adult human pancreatic tissue.

METHODS

Cells were propagated from human pancreatic tissue using a serum-free, low-calcium medium supplemented with NAC and tested for their ability to differentiate when cultured under different growth conditions.

RESULTS

Human pancreatic cell (HPC) cultures coexpressed alpha-amylase, albumin, vimentin, and nestin. The HPC cultures, however, did not express other genes associated with differentiated pancreatic exocrine, duct, or endocrine cells. A number of transcription factors involved in endocrine cell development including Beta 2, Islet-1, Nkx6.1, Pax4, and Pax6 were expressed at variable levels in HPC cultures. In contrast, pancreatic duodenal homeobox factor 1 (Pdx-1) expression was extremely low and at times undetectable. Overexpression of Pdx-1 in HPC cultures stimulated somatostatin, glucagon, and carbonic anhydrase expression but had no effect on insulin gene expression. HPC cultures could form 3-dimensional islet-like cell aggregates, and this was associated with expression of somatostatin and glucagon but not insulin. Cultivation of HPCs in a differentiation medium supplemented with nicotinamide, exendin-4, and/or LY294002, an inhibitor of phosphatidylinositol-3 kinase, stimulated expression of insulin mRNA and protein.

CONCLUSION

These data support the use of intracellular redox modulation for the enrichment of pancreatic stem/progenitor cells capable of self-renewal and endocrine differentiation.

Insulin production by insulin-producing cells induced from embryonic stem cells

AIM: To study the insulin secretion of insulin-producing cells (IPCs) induced from embryonic stem cells (ESCs).

METHODS: ESCs were allowed to grow on mouse fetal fibroblast feeder layer to keep undifferentiated state, and then transferred into serum-free DMEM supplemented with bFGF to form outgrowths in the culture. At day 21 after induction, the outgrowths were incubated in DTZ solution (final concentration, 100 mg/L) for 15 minutes before being observed microscopically. In addition, insulin production was examined immunohistochemically, and its secretion was determined using ELISA. The gene expression of endocrine pancreatic markers, including PDX-1, insulin1, insulin2 and Glut2, was also analyzed by RT-PCR, and the activity of secreted insulin was determined by glucose-reducing experiment on mice.

RESULTS: ESCs grew and formed embryoid bodies at day 4, and the addition of bFGF promoted the differentiation of ESCs into IPCs. The induced IPCs self-assembled to form three-dimentional clusters, and were stained crimson red by DTZ at day 21 after differentiation. They were found to be immunoreactive to insulin, express pancreatic-duodenal homeobox 1 (PDX1) and insulin2 mRNA. They were also able to secrete detectable amounts of active insulin, which could reduce mouse blood glucose significantly.

CONCLUSION: ES cell-induced IPCs can synthesize and secrete active insulin that is able to reduce blood glucose significantly.

Cytological and immunocytochemical characterization of the insulin secreting insulinoma cell line RINm5F

The rat insulinoma cell line RINm5F, an insulin secreting pancreatic beta cell line, has been used as an attractive model for basic studies of the mechanisms of insulin secretion and, more recently, as a model for the development of alternative methods for the treatment of diabetes. To elucidate the cytological properties and expression patterns of hormones of the gastro-entero-pancreatic system, suspensions of RINm5F cells were investigated by various methods including immunocytochemistry on serial semithin sections, quantitative immunocytochemistry, routine electron microscopy, immuno-electron microscopy, in situ hybridization, and TUNEL technique. At the ultrastructural level, several phenotypes of RIm5F cells were characterized by differences in the number, shape, size, and density of their secretory granules. The most common type contained a mixture of round granules varying in size and electron density. A second type predominantly contained relatively large, moderately dense granules. Moreover, a minority of cells was characterized by the occurrence of polymorphous electron dense granules or the complete absence of any secretory granules. The immunohistochemical data showed that, among the established islet hormones, insulin was present in more than 50% of cells, whereas glucagon and somatostatin occurred only sporadically. Though cells positive for pancreatic polypeptide (PP) were not found, PP-related peptides (NPY and PYY) however could be detected in a minority of cells. The great majority of RINm5F cells were immunoreactive for chromogranin B (CgB), followed by insulin, chromogranin A (CgA), and serotonin (5-HT). In addition to intercellular differences in the density of immunostaining, numerous colocalizations of immunoreactivities were found, suggesting that RINm5F cells represent a mixture of subtypes concerning the individual pattern of hormone expression. The present results reveal a wide range of heterogeneity with respect to the morphology and especially the hormone content between individual RINm5F cells.