Targeting Pancreatic Progenitor Cells in Human Embryonic Stem Cell Differentiation for the Identification of Novel Cell Surface Markers

New sources of beta cells are needed in order to develop cell therapies for patients with diabetes. An alternative to forced expansion of post-mitotic beta cells is the induction of differentiation of stem-cell derived progenitor cells that have a natural self-expansion capacity into insulin-producing cells. In order to learn more about these progenitor cells at different stages along the differentiation process in which they become progressively more committed to the final beta cell fate, we took the approach of identifying, isolating and characterizing stage specific progenitor cells. We generated human embryonic stem cell (HESC) clones harboring BAC GFP reporter constructs of SOX17, a definitive endoderm marker, and PDX1, a pancreatic marker, and identified subpopulations of GFP expressing cells. Using this approach, we isolated a highly enriched population of pancreatic progenitor cells from hESCs and examined their gene expression with an emphasis on the expression of stage-specific cell surface markers. We were able to identify novel molecules that are involved in the pancreatic differentiation process, as well as stage-specific cell markers that may serve to define (alone or in combination with other markers) a specific pancreatic progenitor cell. These findings may help in optimizing conditions for ultimately generating and isolating beta cells for transplantation therapy.     

Role of BMP Signaling in Pancreatic Progenitor Differentiation from Human Embryonic Stem Cells

Transplantation of pancreatic progenitors derived from human embryonic stem cells (hESCs) is a promising way to treat diabetes. Strategies to obtain the required cell mass would rely on the up scaling of current differentiation protocols, or the proliferation of committed progenitors. We aimed at finding conditions that maintain a proliferating pancreatic progenitor pool and we assessed the role of BMP4 signaling in this process. hESCs were differentiated into PDX1 positive pancreatic progenitor stage following our established protocol with few modifications, and then the progenitor cells were passaged in a defined proliferation medium (PM). During passage, the effect of BMP4 signaling on the differentiation and proliferation of pancreatic progenitors was examined by RT-PCR and immunofluorescence analysis. We found that PDX1 positive pancreatic progenitors proliferated and gained NKX6.1 expression in the PM, whereas they failed to express NKX6.1 if BMP signaling was inhibited with Noggin. In this latter condition, part of the progenitors rather generated pro-endocrine cells denoted by NGN3 and synaptophysin expression. On the contrary, addition of BMP4 to the PM promoted the early derivation of PDX1 and NKX6.1 coexpressing pancreatic progenitors. Our findings are in line with mouse pancreas development, and indicate that BMP4 signaling is required for the derivation and maintenance of hESC-derived PDX1+NKX6.1+ pancreatic progenitors. These results are instructive for guiding the development of an efficient pancreas differentiation protocol in view of diabetes cell replacement therapy.     

Endothelial Cells in Co-culture Enhance Embryonic Stem Cell Differentiation to Pancreatic Progenitors and Insulin-Producing Cells through BMP Signaling

Endothelial cells (ECs) represent the major component of the embryonic pancreatic niche and play a key role in the differentiation of insulin-producing β cells in vivo. However, it is unknown if ECs promote such differentiation in vitro. We investigated whether interaction of ECs with mouse embryoid bodies (EBs) in culture promotes differentiation of pancreatic progenitors and insulin-producing cells and the mechanisms involved. We developed a co-culture system of mouse EBs and human microvascular ECs (HMECs). An increase in the expression of the pancreatic markers PDX-1, Ngn3, Nkx6.1, proinsulin, GLUT-2, and Ptf1a was observed at the interface between EBs and ECs (EB-EC). No expression of these markers was found at the periphery of EBs cultured without ECs or those co-cultured with mouse embryonic fibroblasts (MEFs). At EB-EC interface, proinsulin and Nkx6.1 positive cells co-expressed phospho-Smad1/5/8 (pSmad1/5/8). Therefore, EBs were treated with HMEC conditioned media (HMEC-CM) suspecting soluble factors involved in bone morphogenetic protein (BMP) pathway activation. Upregulation of PDX-1, Ngn3, Nkx6.1, insulin-1, insulin-2, amylin, SUR1, GKS, and amylase as well as down-regulation of SST were detected in treated EBs. In addition, higher expression of BMP-2/-4 and their receptor (BMPR1A) were also found in these EBs. Recombinant human BMP-2 (rhBMP-2) mimicked the effects of the HMEC-CM on EBs. Noggin (NOG), a BMP antagonist, partially inhibited these effects. These results indicate that the differentiation of EBs to pancreatic progenitors and insulin-producing cells can be enhanced by ECs in vitro and that BMP pathway activation is central to this process.     

PDX1联合NKX6.1促进骨髓间充质干细胞分化为胰岛β样细胞

目的： 为提高骨髓间充质干细胞(BMSCs)向胰腺β样细胞的分化效率,以产生足够用于移植的胰岛样细胞。方法: 构建含PDX1与NKX6.1双基因的重组腺病毒载体,用重组腺病毒感染并联合多种细胞因子分步诱导BMSCs。用RT-PCR、Western blotting等多种方法分别检测PDX1、NKX6.1、胰岛素及C-肽表达情况;观测植入鼠肾包膜下的细胞形态与胰岛素、C-肽等相应分子表达情况以及检测植入细胞对糖尿病模型大鼠的血糖水平的调节能力。结果: BMSCs经重组腺病毒pAdxsi-CMV-PDX1/CMV-NKX6.1联合相应细胞因子分步诱导,双硫腙染色细胞质呈亮红色,RT-PCR显示诱导后的细胞持续稳定表达胰岛素、葡萄糖转运蛋白2(GLUT2)等β细胞相关分子;Western blotting、免疫细胞化学与间接荧光结果亦相似。所诱导的实验组细胞经5.5和25mmol/L葡萄糖刺激后胰岛素分泌水平分别为(1 240.4±109.3) mU/L和(3 539.8±245.1) mU/L, 并显著高于对照组的分泌量。移植实验组细胞可恢复STZ糖尿病小鼠血糖正常水平。结论: PDX1与NKX6.1联合细胞因子在体外能有效地诱导BMSCs分化为胰岛β样细胞;这种胰岛β样细胞移植能有效恢复STZ糖尿病小鼠的血糖正常水平,维持小鼠良好的生存状态,这将为治疗糖尿病带来新的希望。     

Sonic hedgehog and other soluble factors from differentiating embryoid bodies inhibit pancreas development

Success of cell-replacement therapy for diabetes will largely depend on the establishment of alternative sources of pancreatic islet grafts. Embryonic stem (ES) cell differentiation toward pancreatic insulin-producing cells offers such perspectives, but there are still many challenges to overcome. Our previous studies suggested that the limited amount of insulin-positive cells derived from ES cells is related to the activation of pancreas inhibitory signals. To confirm this hypothesis, we report here that exposure of mouse embryonic pancreas explants to soluble factors from embryoid bodies (EBs) inhibits growth, morphogenesis, and endocrine and exocrine differentiation as evaluated by explant size and mRNA and protein expression. Sonic Hedgehog (Shh), an established pancreas repressor both at early and late developmental stages, was produced and secreted by EBs, and participated in the inhibitory effect by inducing its target Gli1 in the explants. Inhibition of Hedgehog pathway rescued the differentiation of Insulin-positive cells in the explants. In contrast to pancreatic cells, hepatic progenitors exposed to EB-conditioned medium showed improved differentiation of albumin-positive cells. In a model system of ES cell differentiation in vitro, we found that definitive endoderm induction by serum removal or activin A treatment further increased Hedgehog production and activity in EBs. Concomitantly, downregulation of the pancreas marker Pdx1 was recorded in activin-treated EBs, a phenomenon that was prevented by antagonizing Hedgehog signaling with Hedgehog interacting protein. These data strongly suggest that Hedgehog production in EBs limits pancreatic fate acquisition and forms a major obstacle in the specification of pancreatic cells from ES-derived definitive endoderm. Disclosure of potential conflicts of interest is found at the end of this article.     

In vitro cultivation of islet-like cell clusters from human umbilical cord blood-derived mesenchymal stem cells

A major obstacle to successful islet transplantation for both type 1 and 2 diabetes is an inadequate supply of insulin-producing tissue. In vitro transdifferentiation of human umbilical cord blood-derived mesenchymal stem cells (UCB-MSCs) into insulin-producing cells could provide an abundant source of cells for this procedure. For this study, we isolated and characterized human UCB-MSCs and induced them in vitro to differentiate into islet-like cell clusters using a 15-day protocol based on a combination of high-glucose, retinoic acid, nicotinamide, epidermal growth factor, and exendin-4. These clusters appeared about 9 days after pancreatic differentiation; expressed pancreatic beta-cell markers, including insulin, glucagon, Glut-2, PDX1, Pax4, and Ngn3; and could synthesize and secrete functional islet proteins at the end of the inducing protocol. The insulin-positive cells accounted for (25.2-3.36)% of whole induced cells. Although insulin secretion of those insulin-producing cells did not respond to glucose challenge very well, human UCB-MSCs have the ability to differentiate into islet-like cells in vitro and may be a potential new source for islet transplantation.     

A novel stepwise differentiation of functional pancreatic exocrine cells from embryonic stem cells

Cultivation of functional pancreatic cells isolated from adult mammalian pancreas remains difficult. We developed a differentiation protocol that gradually induced the formation of mouse pancreatic exocrine cells from embryonic stem cells (ESCs). This process mimicked in vivo pancreatic development by directing cells through definitive endoderm (DE), gut tube endoderm, and pancreatic progenitor cells to differentiated cells that expressed pancreatic exocrine enzymes. Mouse ESCs were cultured in hanging drops to form embryoid bodies. Treatment of embryoid bodies with activin A induced the formation of DE cells that expressed marker mRNAs Goosecoid and Mixl1 and that were double-positive with Foxa2 and Sox17 proteins. Subsequent treatment of the DE cells by retinoic acid induced the formation of gut tube endoderm cells that expressed the specific marker Hnf1b. Expression of Goosecoid and Mixl1 was downregulated during this period. Fibroblast growth factor 7 (FGF7) promoted differentiation of PDX1-expressing pancreatic progenitor cells that also expressed Foxa2 mRNA, an endodermal marker, suggesting derivation from the DE cells. Exocrine cell differentiation was induced with FGF7, glucagon-like peptide-1, and nicotinamide. The differentiated cells expressed mature pancreatic exocrine cell mRNAs, such as Amylase, Elastase, and Carboxypeptidase A. Additionally, they produced pancreatic elastase, amylase, carboxypeptidase A, and chymotrypsin proteins that were identified in cytoplasmic granules by immunocytochemistry. Active amylase was released into the medium. Moreover, FGF7 was associated with differentiation of pancreatic exocrine cells. The findings reported here offer a novel and effective process to develop pancreatic exocrine cells from ESCs.     

利用Tet-On系统构建稳定表达Pdx1的小鼠ESC细胞株

目的:利用Tet-On系统构建稳定表达胰十二指肠同源异形框1(Pdx1)的小鼠胚胎干细胞(ESC)株,为进一步研究Pdx1+定型内胚层细胞向胰腺细胞分化奠定了基础.方法:采用Tet-On系统构建具有绿色荧光蛋白标记及嘌呤霉素抗性的Pdx1过表达慢病毒载体并感染胚胎干细胞.实验分为空白对照组(ESC组)、空载慢病毒对照组...     

Differentiation and transplantation of functional pancreatic Beta cells generated from induced pluripotent stem cells derived from a type 1 diabetes mouse model

The nonobese diabetic (NOD) mouse is a classical animal model for autoimmune type 1 diabetes (T1D), closely mimicking features of human T1D. Thus, the NOD mouse presents an opportunity to test the effectiveness of induced pluripotent stem cells (iPSCs) as a therapeutic modality for T1D. Here, we demonstrate a proof of concept for cellular therapy using NOD mouse-derived iPSCs (NOD-iPSCs). We generated iPSCs from NOD mouse embryonic fibroblasts or NOD mouse pancreas-derived epithelial cells (NPEs), and applied directed differentiation protocols to differentiate the NOD-iPSCs toward functional pancreatic beta cells. Finally, we investigated whether the NPE-iPSC-derived insulin-producing cells could normalize hyperglycemia in transplanted diabetic mice. The NOD-iPSCs showed typical embryonic stem cell-like characteristics such as expression of markers for pluripotency, in vitro differentiation, teratoma formation, and generation of chimeric mice. We developed a method for stepwise differentiation of NOD-iPSCs into insulin-producing cells, and found that NPE-iPSCs differentiate more readily into insulin-producing cells. The differentiated NPE-iPSCs expressed diverse pancreatic beta cell markers and released insulin in response to glucose and KCl stimulation. Transplantation of the differentiated NPE-iPSCs into diabetic mice resulted in kidney engraftment. The engrafted cells responded to glucose by secreting insulin, thereby normalizing blood glucose levels. We propose that NOD-iPSCs will provide a useful tool for investigating genetic susceptibility to autoimmune diseases and generating a cellular interaction model of T1D, paving the way for the potential application of patient-derived iPSCs in autologous beta cell transplantation for treating diabetes.     

Stem cells and diabetes treatment

Diabetes mellitus types 1 and 2 are characterized by absolute versus relative lack of insulin-producing beta cells, respectively. Reconstitution of a functional beta-cell mass by cell therapy--using organ donor islets of Langerhans--has been demonstrated to restore euglycaemia in the absence of insulin treatment. This remarkable achievement has stimulated the search for appropriate stem cell sources from which adequate expansion and maturation of therapeutic beta cells can be achieved. This recent activity is reviewed and presented with particular focus on directed differentiation from pluripotent embryonic stem cells (versus other stem/progenitor cell sources) based on knowledge from pancreatic beta-cell development and the parallel approach to controlling endogenous beta-cell neogenesis.     

Developmental regulation of glucose transporters GLUT3, GLUT4 and GLUT8 in the mouse cerebellar cortex

Glucose uptake into the mammalian nervous system is mediated by the family of facilitative glucose transporter proteins (GLUT). In this work we investigate how the expression of the main neuronal glucose transporters (GLUT3, GLUT4 and GLUT8) is modified during cerebellar cortex maturation. Our results reveal that the levels of the three transporters increase during the postnatal development of the cerebellum. GLUT3 localizes in the growing molecular layer and in the internal granule cell layer. However, the external granule cell layer, Purkinje cell cytoplasm and cytoplasm of the other cerebellar cells lack GLUT3 expression. GLUT4 and GLUT8 have partially overlapping patterns, which are detected in the cytoplasm and dendrites of Purkinje cells, and also in the internal granule cell layer where GLUT8 displays a more diffuse pattern. The differential localization of the transporters suggests that they play different roles in the cerebellum, although GLUT4 and GLUT8 could also perform some compensatory or redundant functions. In addition, the increase in the levels and the area expressing the three transporters suggests that these roles become more important as development advances. Interestingly, the external granule cells, which have been shown to express the monocarboxylate transporter MCT2, express none of the three main neuronal GLUTs. However, when these cells migrate inwardly to differentiate in the internal granule cells, they begin to produce GLUT3, GLUT4 and GLUT8, suggesting that the maturation of the cerebellar granule cells involves a switch in their metabolism in such a way that they start using glucose as they mature.