Evaluation of islets derived from human fetal pancreatic progenitor cells in diabetes treatment
© Zhang et al.; licensee BioMed Central Ltd. 2013
Received: 4 February 2013
Accepted: 14 November 2013
Published: 22 November 2013
With the shortage of donor organs for islet transplantation, insulin-producing cells have been generated from different types of stem cell. Human fetal pancreatic stem cells have a better self-renewal capacity than adult stem cells and can readily differentiate into pancreatic endocrine cells, making them a potential source for islets in diabetes treatment. In the present study, the functions of pancreatic islets derived from human fetal pancreatic progenitor cells were evaluated in vitro and in vivo.
Human pancreatic progenitor cells isolated from the fetal pancreas were expanded and differentiated into islet endocrine cells in culture. Markers for endocrine and exocrine functions as well as those for alpha and beta cells were analyzed by immunofluorescent staining and enzyme-linked immunosorbent assay (ELISA). To evaluate the functions of these islets in vivo, the islet-like structures were transplanted into renal capsules of diabetic nude mice. Immunohistochemical staining for human C-peptide and human mitochondrion antigen was applied to confirm the human origin and the survival of grafted islets.
Human fetal pancreatic progenitor cells were able to expand in medium containing basic fibroblast growth factor (bFGF) and leukemia inhibitor factor (LIF), and to differentiate into pancreatic endocrine cells with high efficiency upon the actions of glucagon-like peptide-1 and activin-A. The differentiated cells expressed insulin, glucagon, glucose transporter-1 (GLUT1), GLUT2 and voltage-dependent calcium channel (VDCC), and were able to aggregate into islet-like structures containing alpha and beta cells upon suspension. These structures expressed and released a higher level of insulin than adhesion cultured cells, and helped to maintain normoglycemia in diabetic nude mice after transplantation.
Human fetal pancreatic progenitor cells have good capacity for generating insulin producing cells and provide a promising potential source for diabetes treatment.
The success of islet transplantation over the last decade suggests that diabetes can be cured by a replenishment of deficient beta cells [1, 2]. However, according to the transplantation protocol of Edmonton, the transplanted islets into each patient should be isolated from two to three pancreatic donors, exceeding ten thousand islet equivalent (IEQ)/kg . As a result, a widespread use of islet transplantation is severely limited by the shortage of donor organs. Stem cells have the capacity of self-renewal and the potential of differentiating into various cell types, making them an ideal candidate to address this issue.
Although the possibility of generating insulin-producing cells routinely from both human embryo stem cells (ESC) and human induced pluripotent stem (iPS) cells is quite encouraging, significant challenges still remain . Lumelsky  and Assady  found that islet-like cells could be generated in vitro by differentiation of ESC under conditions resembling those of physiological development for pancreatic beta cell development. However, insulin secretion by these cells was low and lacked a full response to glucose. Clinically, applying ESC-derived cells in treatment presents more challenges including the risk of cancer formation, functional deficiency of such cells and controversial ethical issues. Deriving insulin-releasing cells from iPS cells poses similar problems. Although several small molecules were able to efficiently induce iPS cells into insulin-producing cells, only about 10% of the cells became productive .
Human adult stem cells derived from various tissues were also explored for generating insulin-producing cells. Kadam et al. expanded mesenchymal stromal cells from human umbilical cord and placenta, and differentiated them into functional islets in vitro. Chandra et al.  reported that islet-like cell aggregates derived from stem cells in human adipose tissue ameliorated experimental diabetes in mice. However, the extent of endocrine cell formation and insulin secretory function were insufficient to become clinically applicable .
It has been demonstrated that stem cells are available in pancreatic ducts and islets, with the capability of differentiating into pancreatic exocrine and endocrine cells [11, 12], and the number of pancreatic stem cells increased upon partial pancreatectomy or destructive immune response . Thus, it is possible that pancreatic stem cells might be promoted to differentiate into functional islet endocrine cells under in vitro culture conditions .
It is known that pancreatic stem cells differentiating toward endocrine cells express pancreatic duodenal homeobox-1(PDX-1) and neurogenin 3. Bonner-Weir et al.  showed that human pancreatic duct cells could be expanded and differentiated into glucose responsive islet tissue in vitro given ITS (insulin, transferrin, selenium), nicotinamide and keratinocyte growth factor. Ramiya et al.  isolated murine pancreatic ductal epithelial cells into culture, and induced them into functional islets containing alpha, beta and delta cells. These resulting islets showed temporal changes in mRNA transcripts for islet cell-associated differentiation markers, responded to glucose challenge in vitro and reversed insulin-dependent diabetes after being implanted into non-obese diabetic mice.
While pancreatic stem cells isolated from adult pancreas have low proliferative capability , fetal pancreatic cells have shown stronger proliferative potential in vitro, even those obtained during the second or third trimester . Moreover, human fetal pancreatic progenitor cells also have the capability of differentiating into insulin-producing cells in vitro[18–20]. In the present study, we demonstrate that pancreatic stem cells isolated from human fetal pancreas have the capacity not only to expand and differentiate extensively into islet endocrine cell in vitro but also to correct high blood glucose efficiently in diabetic animals.
Isolation, purification and identification of human pancreatic progenitor cells
The present study was approved by the Clinical Research Ethics Committee of China-Japan Friendship Hospital and conducted according to the principles of the Declaration of Helsinki. Five human fetal pancreases at the 10th to 12th gestational week were obtained from abortion patients in China-Japan Friendship Hospital, in which one was a spontaneous abortion due to low progesterone level and the other four were intended abortions according to the mothers’ choice. All the tissues were obtained following medical ethics and all with patient informed consent.
Pancreas tissues at the 10th to 12th gestational week were confirmed to be abundant with islet-like structures which were CD133 positive but insulin negative by immunohistochemistry staining. The pancreatic tissues were digested with XI collagenase (Sigma, Shanghai, China), and the islet-like structures extracted were suspended in (D)MEM/F12 (Sigma) in a 35-mm cell culture dish. After slowly hand-shaking the dish, the islet-like structures would move to the middle of the dish and were picked up using a pipette under a stereomicroscope (Nikon, Beijing, China). The islet-like structures were resuspended and cultured in a 37°C, 5% CO2 incubator in (D)MEM/F12 medium containing 5% fetal calf serum for stem cell, 40 μg/L leukemia inhibitor factor (LIF), 10 μg/L basic fibroblast growth factor (bFGF), 10 μg/L epidermal growth factor (EGF), 105 U/L penicillin and 100 mg/L streptomycin  Adherent cells that grew from the islet-like structures after 24 hours were trypsinized for passage with 0.1% trypsin/0.1% ethylenediaminetetraacetic acid (EDTA) solution at confluence. The propagated cells were saved for further study. The control human islets were isolated from a section of pancreas after pancreatectomy from a patient with a pancreatic tumor, as previously described .
RT-PCR was employed to detect the following markers for proliferated stem cells: Oct4, ATP-binding cassette superfamily G member 2 (ABCG2), stem cell factor (SCF), CD133, carbonic anhydrase II (CAII), cytokeratin 19 (CK19), PDX-1 and neurogenin 3. The expression of PDX-1 and Neurogenin 3 (Ngn3) was also confirmed by immunofluorescence staining using goat anti-human PDX-1 antibody (Abcam, Cambridge, MA, USA) and rabbit anti-human Ngn3 antibody (Abcam). After two, five and ten passages, cells were collected to measure the expression levels of smooth muscle actin (SMA), vimentin, stem cell markers (Oct4, PDX-1 and CA II) and mature cell markers (insulin and glucagon) by real-time PCR.
Induced differentiation of human pancreatic progenitor cells
Formation of islet-like structures
After four weeks of directed differentiation, the cells were harvested and aggregated in suspension culture under special conditions. In brief, the cells were resuspended in M199 containing 20% FBS, 1.5 mmol/L Ca2+, 1 mmol/L ATP, 2 mmol/L glutamine, 2 μg/ml laminin, 5 μg/ml Type IV collagen and 3 μg/ml fibronectin. The mixture was transferred to a nontreated flask or siliconized centrifugal tubes and placed into a 37°C, 5% CO2 incubator. Gentle agitation was applied every eight hours. After a 24-hour incubation, small cell aggregations formed and were harvested by centrifugation at 1,200 rpm for eight minutes. The morphology of islet-like structures was examined under a stereomicroscope.
The islets differentiated from progenitor cells were selected manually, embedded in optimal cutting temperature (OCT) compound and prepared into frozen sections. The expressions of insulin and glucagon were examined and compared with adult islets as control. The frozen sections were then fixed for one minute with alcohol (95%), washed three times with PBS solution and blocked for 30 minutes at room temperature with 0.1% BSA/PBS. Then anti-insulin and anti-glucagon antibodies (Sigma) were incubated overnight, respectively, with the cells at 4°C. After the sections were rinsed three times with PBS solution, Alex488-labeled secondary antibody (Invitrogen Inc, Grand Island, NK, USA) was added and incubated with the cells for another 30 minutes. A fluorescent microscope was used to observe the results.
Transmission electron microscopy
Adult islets and differentiated cells were collected by centrifugation and washed with PBS, then fixed with 2.5% glutaraldehyde for 30 minutes at room temperature. Cells were washed, post-fixed, dehydrated and embedded with Epon 812 (Electron Microscopy Sciences, Beijing, China). The sections were examined under a JEM-1010 electron microscope (JEOL Inc, Tokyo, Japan). Five fields were examined for each sample.
Total RNA was extracted from cells 0, 3 and 4 weeks post differentiation and from islet-like structures 4 weeks post differentiation using a RNEasy Mini kit (Qiagen Inc, Hilden, Germany). A total of 1 μg RNA was used for reverse transcription using omniscript reverse transcriptase (Qiagen). Real-time PCR was performed on an Applied Biosystems instrument (ABI 7500 system), using SYBR Green PCR Master Mix (ABI Inc, Foster city, CA, USA) and 40 reaction cycles. Markers for pancreatic stem cells, endocrine, exocrine and mesenchymal cells were measured at different time points of expansion and differentiation At the end of each reaction, melting-curve analysis was performed to confirm the absence of primer dimers. The expression levels of genes of interest were normalized to the expression level of GAPDH. Data were analyzed using the 2- Δ Ct method. The pancreatic stem cell markers (CAII, PDX-1, Neurogenin 3; endocrine markers: insulin, glucagon, GLUT1, GLUT2 and VDCC), as well as exocrine markers (HES-1 and amylase) were evaluated during differentiation. The mesenchymal markers SMA and vimentin were evaluated during pancreatic stem cell expansion. The gene-specific primer sequences are shown in additional file (see Additional file 1).
Insulin release assay by ELISA
After pre-incubation with Krebs-Ringer buffer at 37°C for 90 minutes, the progenitor cell-derived islets (100 IEQs/ml) were incubated with Krebs-Ringer buffer containing 2.5 mM glucose or 25 mM glucose at 37°C for different durations. Conditioned medium was then collected, centrifuged and assayed for insulin content by an ELISA kit (Linco Inc, St Charles, MO, USA).
Diabetic animal models
The animal study was approved by the Animal Ethics Committee of China-Japan Friendship Hospital. Twelve male nude BALB/c mice, four- to six-weeks-old, were purchased from Vital River Laboratories (quality certificate: SCXK (Beijing) 20060009)–. All animals were housed in the specific pathogen free (SPF) facility of the Institute of Clinical Research at our hospital. The diabetic model was induced in the mice by an intraperitoneal injection of streptozocin (200 mg/kg body weight; Sigma, St. Louis, MO, USA) freshly dissolved in citrate buffer (pH 4.5). Blood samples were taken from the tail vein of the animals under non-fasting conditions (8:00 A.M.; standard laboratory diet ad libitum overnight) and examined for blood sugar level using a glucometer (Onetouch®Ultra Easy™, Johnson & Johnson, Shanghai, China). Only animals exhibiting blood glucose concentrations >20 mM in three consecutive measurements were employed in the study. They were assigned randomly into a control group and a progenitor cell-derived islet group (n = 6 each).
Transplantation of differentiated islet-like structures
To evaluate the function of progenitor cell-derived islet-like structures, they were transplanted under the capsule of the left kidney of diabetic mice. Blood glucose was measured regularly after transplantation. When euglycemia was maintained for one week, the left kidney with transplants was excised surgically and examined by immunohistochemistry for human C-peptide and human mitochondrion antigen as described below. Blood glucose was monitored regularly after surgery.
In order to verify further the functionality of human pancreatic progenitor cell-derived beta cells in vivo, the animals were sacrificed at the end of experiment. Left murine kidneys were embedded in paraffin. Then murine kidneys were immunostained for human C-peptide (mouse anti-human C-peptide, Chemicon, Temecula, CA, USA) and human mitochondrion antigen (mouse anti-human mitochondrion, Millipore, Billerica, MA, USA) to confirm the survival and functionality of transplanted human islet-like structures.
The analysis was conducted with SPSS11.0 software and the data were expressed as mean ± SD. The t test was uesed for comparison between two groups and one way analysis of variance (ANOVA) for comparisons among multiple groups. P <0.05 and P <0.01 denoted statistical significance.
Isolation, purification and identification of pancreatic progenitor cells
To confirm the expansion of pancreatic progenitor cells rather than mesenchymal cells, the cells from the second, fifth and tenth passages were measured for expressions of SMA, vimentin and stem cells markers. The results showed that stem cell markers Oct4, CAII and PDX-1 did not fluctuate during expansion. SMA and vimentin could be detected at passage two and the expression levels were maintained during expansion (see Additional file 2) but insulin and glucagon were not detectable in these cells.
Differentiation of pancreatic progenitor cells
Quantitative analysis of various gene transcripts during differentiation
Formation of islet-like structures in vitro
Insulin-releasing function of differentiated cells in vitro
Functions of differentiated cells in vivo
This evidence suggests that the islet-like structures derived from human fetal pancreatic progenitor cell can survive and function in vivo.
Pancreatic β cell dysfunction and/or loss of pancreatic β cell mass are key pathogenic factors for diabetes mellitus. Although a preferred therapeutic strategy, islet transplantation has been impeded by limited supply. Therefore, interest in generating insulin-producing cells efficiently became inevitable. Our study shows that human fetal pancreatic progenitor cells can be expanded extensively and differentiated into pancreatic endocrinal cells and islet-like structures in vitro. After transplantation of such structures into diabetic animals, euglycemia can be successfully restored and maintained.
It has been reported that LIF, important for self-renewal, can maintain stem cells in an undifferentiated stage  and bFGF plays a crucial role in cell proliferation and differentiation during embryonic development . Therefore, we expanded human fetal pancreatic progenitor cells in vitro using culture medium containing LIF and bFGF. Our study shows that human fetal pancreatic progenitor cells exhibit a strong proliferation capability in this culture medium. The number of these cells from one single human fetal pancreas could be expanded to 1 × 1010.
During expansion, mesenchymal cell markers of SMA and vimentin became positive at passage two and stayed at the same level during the entire period. Due to the high expression of stem cell marker in these cells, EMT was suspected. Human pancreatic progenitors were reported to transform into mesenchymal-like cells through EMT in a growth-promoting medium. Upon reversal of EMT, these cells could form islet-like aggregates of hormone-producing cells [17, 23].
Similar to adult pancreatic stem cells, human fetal pancreatic progenitor cells expressed PDX-1 and neurogenin-3. As a marker related to islet differentiation, PDX-1 was expressed during differentiation into endocrine cells [15, 24]. Other studies indicated that embryonic stem cells differentiating into insulin-producing cells were also nestin positive . As a poly(ADP-ribose) synthetase inhibitor, nicotinamide promotes cell differentiation and the expressions of insulin and C peptide . Thus, it has been widely used in studies of stem cells differentiating into the pancreatic endocrine lineage. Glucagon-like peptide-1, all-trans retinoic acid and activin A also have been demonstrated to be effective in inducing embryonic stem cell transformation into insulin-producing cells . After induction of human fetal pancreatic progenitor cells with nicotinamide, glucagon-like peptide-1, all-trans retinoic acid and activin A, the expression of mature endocrine cell markers, such as insulin, glucagon, GLUT2 and VDCC, increased extensively and became further up-regulated in islet-like structures.
It was found that islet-like structures formed when differentiated endocrine cells were cultured in suspension with medium containing extracellular matrix molecules, such as laminin, collagen IV and fibronectin. The extracellular matrix molecules mediated adherence between β cells and contributed to proliferation and differentiation into insulin-producing cell . They could also enhance islets survival, insulin expression and release in response to glucose [28–30].
The insulin-releasing response to glucose (25 mM) was found in differentiated cells and it was even stronger in differentiated islet-like structures. Our previous study showed that alpha-cell loss from islets impaired insulin secretion in vitro and in vivo. In the present study, immunofluorescent staining revealed that islet-like structures contained both alpha and beta cells. However, the distribution of alpha cells in the islet-like structures was different from that in native islets.
It is known that insulin-producing cells derived from human embryonic stem cells or human pancreatic islet progenitor cells could correct hyperglycemia in diabetic mice [32, 33]. In the present study, differentiated islet-like structures derived from human fetal pancreatic progenitor cells could release insulin upon in vitro stimulation with glucose and corrected hyperglycemia in diabetic animals in vivo. Furthermore, histological examination revealed that the grafted islet-like structures were of human origin and immune-positive for human C-peptide.
With an excellent capacity for proliferation, human fetal pancreatic progenitor cells may be induced to differentiate into insulin-producing cells and form islet-like structures in vitro. Capable of secreting insulin to reduce hyperglycemia after transplantation in diabetic animals, the resulting islets might become a potential source for islets transplantation in treatment for diabetes.
ATP-binding cassette superfamily G member 2
Basic fibroblast growth factor
Bovine serum albumin
Carbonic anhydrase II
(Dulbecco’s) modified Eagle’s medium
Epidermal growth factor
Enzyme-linked immunosorbent assay
Epithelial to mesenchymal transition
Embryonic stem cells
Fetal bovine serum
Induced pluripotent stem
Leukemia inhibitor factor
Pancreatic duodenal homeobox-1
Real time-polymerase chain reaction
Stem cell factor
Smooth muscle actin
Voltage-dependent calcium channel.
This study was supported by the National Basic Research Program of China (2012CB966402); Key New Drug Creation & Manufacture Program (No.2011ZX09102-010-03); National Nature Science Foundation of China (No. 81370873 and 81370918) and Guangxi Scientific Research and Technology Development Program (No. 2014BC15007). We thank Lin Pan for excellent technical assistance with immunohistochemistry.
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