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

Adult muscle-derived stem cells engraft and differentiate into insulin-expressing cells in pancreatic islets of diabetic mice

Background

Pancreatic beta cells are unique effectors in the control of glucose homeostasis and their deficiency results in impaired insulin production leading to severe diabetic diseases. Here, we investigated the potential of a population of nonadherent muscle-derived stem cells (MDSC) from adult mouse muscle to differentiate in vitro into beta cells when transplanted as undifferentiated stem cells in vivo to compensate for beta-cell deficiency.

Results

In vitro, cultured MDSC spontaneously differentiated into insulin-expressing islet-like cell clusters as revealed using MDSC from transgenic mice expressing GFP or mCherry under the control of an insulin promoter. Differentiated clusters of beta-like cells co-expressed insulin with the transcription factors Pdx1, Nkx2.2, Nkx6.1, and MafA, and secreted significant levels of insulin in response to glucose challenges. In vivo, undifferentiated MDSC injected into streptozotocin (STZ)-treated mice engrafted within 48 h specifically to damaged pancreatic islets and were shown to differentiate and express insulin 10–12 days after injection. In addition, injection of MDSC into hyperglycemic diabetic mice reduced their blood glucose levels for 2–4 weeks.

Conclusion

These data show that MDSC are capable of differentiating into mature pancreatic beta islet-like cells, not only upon culture in vitro, but also in vivo after systemic injection in STZ-induced diabetic mouse models. Being nonteratogenic, MDSC can be used directly by systemic injection, and this potential reveals a promising alternative avenue in stem cell-based treatment of beta-cell deficiencies.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-017-0539-9) contains supplementary material, which is available to authorized users.

MicroRNA-125b-2 overexpression represses ectodermal differentiation of mouse embryonic stem cells

microRNAs (miRNAs or miRS) have been demonstrated to be essential for neural development. miR-125b-2, presented on human chromosome 21, is overexpressed in neurons of individuals with Down syndrome (DS) with cognitive impairments. It has been reported that miR-125b-2 promotes specific types of neuronal differentiation; however, the function of miR-125b-2 in the early development of the embryo has remained to be fully elucidated. In the present study, a mouse embryonic stem cell (mESC) line was stably transfected with a miR-125b-2 lentiviral expression vector and found that miR-125b-2 overexpression did not affect the self-renewal or proliferation of mESCs. However, miR-125b-2 overexpression inhibited the differentiation of mESCs into endoderm and ectoderm. Finally, miR-125b-2 overexpression was found to impair all-trans-retinoic acid-induced neuron development in embryoid bodies. The findings of the present study implied that miR-125b-2 overexpression suppressed the differentiation of mESCs into neurons, which highlights that miR‑125b-2 is important in the regulation of ESC differentiation. The present study provided a basis for the further identification of novel targets of miR-125b-2, which may contribute to an enhanced understanding of the molecular mechanisms of ESC differentiation.

Phenotypic and functional characterization of glucagon-positive cells derived from spontaneous differentiation of D3-mouse embryonic stem cells

BACKGROUND

Glucagon expression is being considered as a definitive endoderm marker in protocols aiming to obtain insulin-secreting cells from embryonic stem cells. However, it should be considered that in vivo glucagon is expressed both in definitive endoderm- and neuroectoderm-derived cells. Therefore, the true nature and function of in vitro spontaneously differentiated glucagon-positive cells remains to be established.

METHODS

D3 and R1 mouse embryonic stem cells as well as α-TC1-9 cells were cultured and glucagon expression was determined by real-time PCR and immunocytochemistry. Functional analyses regarding intracellular calcium oscillations were performed to further characterize glucagon(+) cells.

RESULTS

Specifically, 5% of D3 and R1 cells expressed preproglucagon, with a small percentage of these (<1%) expressing glucagon-like peptide 1. The constitutive expression of protein convertase 5 supports the expression of both peptides. Glucagon(+) cells co-expressed neurofilament middle and some glucagon-like peptide-1(+) cells, glial fibrillary acidic protein, indicating a neuroectodermic origin. However, few glucagon-like peptide-1(+) cells did not show coexpression with glial fibrillary acidic protein, suggesting a non-neuroectodermic origin for these cells. Finally, glucagon(+) cells did not display Ca(2+) oscillations typical of pancreatic α-cells.

DISCUSSION

These results indicate the possible nondefinitive endodermal origin of glucagon-positive cells spontaneously differentiated from D3 and R1 cell lines, as well as the presence of cells expressing glucagon-like peptide-1 from two different origins.

Embryonic stem cells are redirected to non-tumorigenic epithelial cell fate by interaction with the mammary microenvironment

Experiments were conducted to redirect mouse Embryonic Stem (ES) cells from a tumorigenic phenotype to a normal mammary epithelial phenotype in vivo. Mixing LacZ-labeled ES cells with normal mouse mammary epithelial cells at ratios of 1∶5 and 1∶50 in phosphate buffered saline and immediately inoculating them into epithelium-divested mammary fat pads of immune-compromised mice accomplished this. Our results indicate that tumorigenesis occurs only when normal mammary ductal growth is not achieved in the inoculated fat pads. When normal mammary gland growth occurs, we find ES cells (LacZ+) progeny interspersed with normal mammary cell progeny in the mammary epithelial structures. We demonstrate that these progeny, marked by LacZ expression, differentiate into multiple epithelial subtypes including steroid receptor positive luminal cells and myoepithelial cells indicating that the ES cells are capable of epithelial multipotency in this context but do not form teratomas. In addition, in secondary transplants, ES cell progeny proliferate, contribute apparently normal mammary progeny, maintain their multipotency and do not produce teratomas.

Reversible immortalization of Nestin-positive precursor cells from pancreas and differentiation into insulin-secreting cells

Pancreatic stem cells or progenitor cells posses the ability of directed differentiation into pancreatic β cells. However, these cells usually have limited proliferative capacity and finite lifespan in vitro. In the present study, Nestin-positive progenitor cells (NPPCs) from mouse pancreas that expressed the pancreatic stem cells or progenitor cell marker Nestin were isolated to obtain a sufficient number of differentiated pancreatic β cells. Tet-on system for SV40 large T-antigen expression in NPPCs was used to achieve reversible immortalization. The reversible immortal Nestin-positive progenitor cells (RINPPCs) can undergo at least 80 population doublings without senescence in vitro while maintaining their biological and genetic characteristics. RINPPCs can be efficiently induced to differentiate into insulin-producing cells that contain a combination of glucagon-like peptide-1 (GLP-1) and sodium butyrate. The results of the present study can be used to explore transplantation therapy of type I diabetes mellitus.

Specific Effect of 5-Fluorouracil on α-Fetoprotein Gene Expression During the In Vitro Mouse Embryonic Stem Cell Differentiation

Embryonic stem (ES) cells are considered an important alternative to develop in vitro screening methods for embryotoxicity. Mouse ES cells can be cultured as cell suspension aggregates termed “embryoid bodies” (EBs) in which cells start to differentiate. We have studied the expression of several genes in the presence of a wide range of concentrations of 5-fluorouracil (5-FU). This well-established embryotoxic compound completely inhibited cell viability at 200 nmol/L in monolayer cultures. At lower concentrations, 5-FU led to decrease in the expression of the α-fetoprotein gene, a marker of the visceral endoderm, in the EBs. However, the expression of several mesodermal gene markers was not significantly affected at these concentrations. These results suggest a high sensitivity of the visceral endoderm differentiation to 5-FU. Therefore, the quantification of the α-fetoprotein gene after exposure to potential embryotoxicants should be considered an additional end point in future embryotoxicity assays in vitro with ES cells.

Insulin - producing cells derived from stem cells: recent progress and future directions

Type 1 diabetes is characterized by the selective destruction of pancreatic β-cells caused by an autoimmune attack. Type 2 diabetes is a more complex pathology which, in addition to β-cell loss caused by apoptotic programs, includes β-cell dedifferentiation and peripheric insulin resistance. β-Cells are responsible for insulin production, storage and secretion in accordance to the demanding concentrations of glucose and fatty acids. The absence of insulin results in death and therefore diabetic patients require daily injections of the hormone for survival. However, they cannot avoid the appearance of secondary complications affecting the peripheral nerves as well as the eyes, kidneys and cardiovascular system. These afflictions are caused by the fact that external insulin injection does not mimic the tight control that pancreaticderived insulin secretion exerts on the body’s glycemia. Restoration of damaged β-cells by transplantation from exogenous sources or by endocrine pancreas regeneration would be ideal therapeutic options. In this context, stem cells of both embryonic and adult origin (including β-cell/islet progenitors) offer some interesting alternatives, taking into account the recent data indicating that these cells could be the building blocks from which insulin secreting cells could be generated in vitro under appropriate culture conditions. Although in many cases insulin-producing cells derived from stem cells have been shown to reverse experimentally induced diabetes in animal models, several concerns need to be solved before finding a definite medical application. These refer mainly to the obtainment of a cell population as similar as possible to pancreatic β-cells, and to the problems related with the immune compatibility and tumor formation. This review will summarize the different approaches that have been used to obtain insulin-producing cells from embryonic and adult stem cells, and the main problems that hamper the clinical applications of this technology.

An efficient experimental strategy for mouse embryonic stem cell differentiation and separation of a cytokeratin-19-positive population of insulin-producing cells

OBJECTIVES

Embryonic stem cells are a potential source for insulin-producing cells, but existing differentiation protocols are of limited efficiency. Here, the aim has been to develop a new one, which drives development of embryonic stem cells towards insulin-producing cells rather than to neuronal cell types, and to combine this with a strategy for their separation from insulin-negative cells.

MATERIALS AND METHODS

The cytokeratin-19 (CK19) promoter was used to control the expression of enhanced yellow fluorescence protein in mouse embryonic stem cells during their differentiation towards insulin-producing cells, using a new optimized four-stage protocol. Two cell populations, CK19(+) and CK19(-) cells, were successfully fluorescence sorted and analysed.

RESULTS

The new method reduced neuronal progeny and suppressed differentiation into glucagon- and somatostatin-producing cells. Concomitantly, beta-cell like characteristics of insulin-producing cells were strengthened, as documented by high gene expression of the Glut2 glucose transporter and the transcription factor Pdx1. This novel protocol was combined with a cell-sorting technique. Through the combined procedure, a fraction of glucose-responsive insulin-secreting CK19(+) cells was obtained with 40-fold higher insulin gene expression and 50-fold higher insulin content than CK19(-) cells. CK19(+) cells were immunoreactive for C-peptide and had ultrastructural characteristics of an insulin-secretory cell.

CONCLUSION

Differentiated CK19(+) cells reflect an endocrine precursor cell type of ductal origin, potentially suitable for insulin replacement therapy in diabetes.

Cell therapy for diabetes mellitus: an opportunity for stem cells?

Diabetes is a chronic disease characterized by a deficit in beta cell mass and a failure of glucose homeostasis. Both circumstances result in a variety of severe complications and an overall shortened life expectancy. Thus, diabetes represents an attractive candidate for cell therapy. Reversal of diabetes can be achieved through pancreas and islet transplantation, but shortage of donor organs has prompted an intensive search for alternative sources of beta cells. This achievement has stimulated the search for appropriate stem cell sources. Both embryonic and adult stem cells have been used to generate surrogate beta cells or otherwise restore beta cell functioning. In this regard, several studies have reported the generation of insulin-secreting cells from embryonic and adult stem cells that normalized blood glucose values when transplanted into diabetic animal models. Due to beta cell complexity, insulin-producing cells generated from stem cells do not possess all beta cell attributes. This indicates the need for further development of methods for differentiation and selection of completely functional beta cells. While these problems are overcome, diabetic patients may benefit from therapeutic strategies based on autologous stem cell therapies addressing late diabetic complications. In this article, we discuss the recent progress in the generation of insulin-producing cells from embryonic and adult stem cells, together with the challenges for the clinical use of diabetes stem cell therapy.

Gap junctional intercellular communication is required to maintain embryonic stem cells in a non-differentiated and proliferative state

Pluripotent embryonic stem (ES) cells are capable of maintaining a self-renewal state and have the potential to differentiate into derivatives of all three embryonic germ layers. Despite their importance in cell therapy and developmental biology, the mechanisms whereby ES cells remain in a proliferative and pluripotent state are still not fully understood. Here we establish a critical role of gap junctional intercellular communication (GJIC) and connexin43 (Cx43) in both processes. Pharmacological blockers of GJIC and Cx43 down-regulation by small interfering RNA (siRNA) caused a profound inhibitory effect on GJIC, as evidenced by experiments of fluorescence recovery after photobleaching. This deficient intercellular communication in ES cells induced a loss of their pluripotent state, which was manifested in morphological changes, a decrease in alkaline phosphatase activity, Oct-3/4 and Nanog expression, as well as an up-regulation of several differentiation markers. A decrease in the proliferation rate was also detected. Under these conditions, the formation of embryoid bodies from mouse ES cells was impaired, although this inhibition was reversible upon restoration of GJIC. Our findings define a major function of GJIC in the regulation of self-renewal and maintenance of pluripotency in ES cells.

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.

Developmental potential of Gcn5(-/-) embryonic stem cells in vivo and in vitro

Gcn5 is a prototypical histone acetyltransferase (HAT) that serves as a coactivator for multiple DNA-bound transcription factors. We previously determined that deletion of Gcn512 (hereafter referred to as Gcn5) causes embryonic lethality in mice. Gcn5 null embryos undergo gastrulation but exhibit high levels of apoptosis, leading to loss of mesodermal lineages. To further define the functions of Gcn5 during development, we created Gcn5(-/-) mouse embryonic stem (ES) cells. These cells survived in vitro and formed embryoid bodies (EBs) that expressed markers for ectodermal, mesodermal, and endodermal lineages. Gcn5(-/-) EBs were misshapen and smaller than wild-type EBs by day 6, with an increased proportion of cells in G2/M. Expression of Oct 4 and Nodal was prematurely curtailed in Gcn5(-/-) EBs, indicating early loss of pluripotent ES cells. Gcn5(-/-) EBs differentiated efficiently into skeletal and cardiac muscle, which derive from mesoderm. High percentage Gcn5(-/-) chimeric embryos created by injection of Gcn5(-/-) ES cells into wild-type blastocysts were delayed in development and died early. Interestingly, elevated levels of apoptosis were observed specifically in Gcn5 null cells within the chimeric embryos. Collectively, these data indicate that Gcn5 may be required to maintain pluripotent states and that loss of Gcn5 invokes a cell-autonomous pathway of cell death in vivo.

Possibility of insulin-producing cells derived from mouse embryonic stem cells for diabetes treatment

Insulin injection therapy is the principal current treatment of type 1 diabetes. Patients, however, suffer from various complications generated by insufficient control of blood glucose levels over a long period. Therefore, a method which can infuse insulin in response to changes of blood glucose levels is eagerly desired. Transplantation of insulin releasing cells derived from embryonic stem (ES) cells has been expected to be one of promising approaches to realize this requirement. In this study, ES cell progeny which were derived in culture media with/without fetal calf serum contained two distinct kinds of cells immunostained by anti-insulin and anti-C-peptide antibodies. The cytoplasm and nuclei of one type of cell were immunoreactive against antibodies for insulin, while the other kind of cell only had the cytoplasm stained by the anti-insulin antibody. The first cell type was the major population of insulin-positive cells in serum-free medium, while the latter kind of cells was the major population in medium containing serum. Interestingly, the latter insulin-positive cells could be also immunostained by anti-C-peptide antibodies, and was observed even after nine subcultures in medium containing serum. Although there still remain many issues to be addressed in order to definitely demonstrate that insulin-positive cells derived from ES cells to be truly beta cells in the islets, these properties of the obtained cells are believed to promising cells for treatment of type 1 diabetes.

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.

Production of pancreatic hormone-expressing endocrine cells from human embryonic stem cells

Of paramount importance for the development of cell therapies to treat diabetes is the production of sufficient numbers of pancreatic endocrine cells that function similarly to primary islets. We have developed a differentiation process that converts human embryonic stem (hES) cells to endocrine cells capable of synthesizing the pancreatic hormones insulin, glucagon, somatostatin, pancreatic polypeptide and ghrelin. This process mimics in vivo pancreatic organogenesis by directing cells through stages resembling definitive endoderm, gut-tube endoderm, pancreatic endoderm and endocrine precursor--en route to cells that express endocrine hormones. The hES cell-derived insulin-expressing cells have an insulin content approaching that of adult islets. Similar to fetal beta-cells, they release C-peptide in response to multiple secretory stimuli, but only minimally to glucose. Production of these hES cell-derived endocrine cells may represent a critical step in the development of a renewable source of cells for diabetes cell therapy.

Insulin - producing cells derived from stem cells: recent progress and future directions

Type 1 diabetes is characterized by the selective destruction of pancreatic beta-cells caused by an autoimmune attack. Type 2 diabetes is a more complex pathology which, in addition to beta-cell loss caused by apoptotic programs, includes beta-cell dedifferentiation and peripheric insulin resistance. beta-Cells are responsible for insulin production, storage and secretion in accordance to the demanding concentrations of glucose and fatty acids. The absence of insulin results in death and therefore diabetic patients require daily injections of the hormone for survival. However, they cannot avoid the appearance of secondary complications affecting the peripheral nerves as well as the eyes, kidneys and cardiovascular system. These afflictions are caused by the fact that external insulin injection does not mimic the tight control that pancreatic-derived insulin secretion exerts on the body's glycemia. Restoration of damaged beta-cells by transplantation from exogenous sources or by endocrine pancreas regeneration would be ideal therapeutic options. In this context, stem cells of both embryonic and adult origin (including beta-cell/islet progenitors) offer some interesting alternatives, taking into account the recent data indicating that these cells could be the building blocks from which insulin secreting cells could be generated in vitro under appropriate culture conditions. Although in many cases insulin-producing cells derived from stem cells have been shown to reverse experimentally induced diabetes in animal models, several concerns need to be solved before finding a definite medical application. These refer mainly to the obtainment of a cell population as similar as possible to pancreatic beta-cells, and to the problems related with the immune compatibility and tumor formation. This review will summarize the different approaches that have been used to obtain insulin-producing cells from embryonic and adult stem cells, and the main problems that hamper the clinical applications of this technology.

Proinsulin in development: New roles for an ancient prohormone

In postnatal organisms, insulin is well known as an essential anabolic hormone responsible for maintaining glucose homeostasis. Its biosynthesis by the pancreatic beta cell has been considered a model of tissue-specific gene expression. However, proinsulin mRNA and protein have been found in embryonic stages before the formation of the pancreatic primordium, and later, in extrapancreatic tissues including the nervous system. Phylogenetic studies have also confirmed that production of insulin-like peptides antecedes the morphogenesis of a pancreas, and that these peptides contribute to normal development. In recent years, other roles for insulin distinct from its metabolic function have emerged also in vertebrates. During embryonic development, insulin acts as a survival factor and is involved in early morphogenesis. These findings are consistent with the observation that, at these stages, the proinsulin gene product remains as the precursor form, proinsulin. Independent of its low metabolic activity, proinsulin stimulates proliferation in developing neuroretina, as well as cell survival and cardiogenesis in early embryos. Insulin/proinsulin levels are finely regulated during development, since an excess of the protein interferes with correct morphogenesis and is deleterious for the embryo. This fine-tuned regulation is achieved by the expression of alternative embryonic proinsulin transcripts that have diminished translational activity.

How can we get more beta cells?

The need for a reliable source of functional beta cells has led to many new investigations in an effort to drive the differentiation of embryonic stem cells, of putative stem cells, or of pancreatic progenitor cells to form new beta cells. There appears to be a plasticity of pancreatic cells in vitro that may be exploited to generate the necessary beta cells. Major questions still remain: whether there are true pancreatic stem cells, what are the pancreatic progenitor cells after birth, and whether expanded beta cells themselves could serve as the source.

ISOLATION AND CHARACTERIZATION OF RESIDUAL UNDIFFERENTIATED MOUSE EMBRYONIC STEM CELLS FROM EMBRYOID BODY CULTURES BY FLUORESCENCE TRACKING

The differentiation of mouse embryonic stem (ES) cells can be induced in vitro after leukemia inhibitory factor (LIF) withdrawal and further enhanced by the formation of "embryoid body" (EB) aggregates. This strategy is being used in order to optimize differentiation protocols that would result in functional cells for experimental cell replacement therapies. However, this study presents the possibility for residual undifferentiated cells to survive after standard in vitro procedures. Mouse ES cells were stably transfected with the enhanced green fluorescent protein (EGFP), under the control of the Oct4 promoter, a transcription factor that is expressed in undifferentiated ES cells but down-regulated on differentiation. Residual fluorescent cells were isolated from EBs that were cultured in standard conditions in absence of LIF. These residual cells displayed recurrent gain of chromosomes 8 and 9. Residual fluorescent cells, further expanded in absence of LIF and cultured as EBs, still displayed a significant Oct4 expression in comparison with parental transfected ES cells. Consequently, these residual cells have an intrinsic resistance to differentiate. The behavior of these cells, observed in vitro, can be overcome in vivo, as they were able to induce teratomas in subcutaneously injected nude mice. Residual undifferentiated cells displayed slight levels of VASA and DAZL expression. These results demonstrate that mouse ES cells cultured in vitro, in standard conditions, can spontaneously acquire recurrent karyotypical changes that may promote an undifferentiated stage, being selected in standard culture conditions in vitro.