The Use of Animal Models to Study Stem Cell Therapies for Diabetes Mellitus
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The Use of Animal Models to Study Stem Cell Therapies for Diabetes Mellitus
Woo-Jin Song, Rohan Shah, and Mehboob A. Hussain
Abstract solute (type 1) and a relative (type 2) reduction in functional
insulin-producing β cell mass in the islets of Langerhans in
The two main forms of human diabetes mellitus (DM) are char- the pancreas. Type 1 DM results from autoimmune assault of
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acterized by an absolute (type 1) and a relative (type 2) reduc- β cells, and type 2 from the failure of pancreatic β cells to
tion in functional insulin-producing β cell mass in the pancreas. sufficiently compensate for insulin resistance. Studies in
Type 1 DM results from autoimmune assault of β cells, and Europe indicate an increasing incidence of type 1 DM in
type 2 from the failure of pancreatic β cells to sufficiently com- children in the past 15 years, and projections for 2005–2020
pensate for insulin resistance. Studies indicate that the inci- estimate a doubling of new cases in children younger than
dence of both types is increasing rapidly to levels that constitute 5 years and an increase of approximately 70% in children
a global epidemic. Researchers are experimentally developing younger than 15 (Patterson et al. 2009). The incidence of
several conceptual approaches for increasing pancreatic β cell type 2 DM is also increasing rapidly and is now considered
mass and testing them for feasibility in treating the disease. The a global epidemic; in the United States there is an estimated
main sources for derivation of insulin-producing cells are em- 25-30% lifetime risk of developing the disease.
bryonic and induced pluripotent stem cells, endogenous pro- Efforts to develop treatments for the disease rely on
genitor cells (both within and outside the pancreas), stimulation chemically induced animal (primarily rodent) models in
of β cell proliferation, and genetic “reprogramming” of cells. which endogenous β cells are destroyed, most often by phar-
Strategies to effectively address immune- and inflammation- macologic toxin administration. β cell destruction results in
mediated assault on existing and newly formed β cells need to lack of insulin production and pronounced hyperglycemia,
be refined. This review provides a description of β cell ablation which, if untreated, leads to the death of the animal. Insulin-
methods and a discussion of various types of studies of regen- producing cells, derived from a variety of sources, are tested
erative approaches—β cell proliferation, islet cell transplanta- in these diabetic animals to assess the extent of recovery
tion, transdifferentiation, and the use of embryonic and induced from hyperglycemia.
pluripotent stem cells—to the treatment of diabetes mellitus. Although the derivation of insulin-producing cells from
Although there has been much progress in this area, further re- precursor cells is apparently becoming a feasible approach,
search is needed to enhance understanding and improve thera- considerable challenges remain in the treatment of diabetes
peutic strategies for this widespread disease. mellitus. For example, it is unclear whether newly generated
β cells may form tumors and/or be able to function as well as
Key Words: ablation; β cell; diabetes mellitus; progenitor; endogenous β cells in the islets of Langerhans. The studies
proliferation; reprogramming; stem cells; transdifferentiation described below attempt to address these and other questions
about possible DM treatment strategies.
Introduction
β Cell Ablation Methods
D
iabetes mellitus (DM1) is increasingly widespread in
the United States and Europe. The two main forms
In vivo functional testing of insulin-producing cells is per-
of the disease in humans are characterized by an ab-
formed in animals whose endogenous β cells have been ab-
lated, either partially (for studies of regeneration from
residual β cells) or completely (for studies of de novo gen-
Woo-Jin Song, MS, is a graduate student in the Graduate Program in
Biological Chemistry in the Department of Pediatrics; Rohan Shah is an
eration of β cells).
undergraduate student in the Biomedical Engineering Department; and
Mehboob A. Hussain, MD, is an associate professor in the Departments of
Pediatrics, Medicine, and Biological Chemistry, all at the Johns Hopkins Chemical Ablation
University in Baltimore, Maryland.
Address correspondence and reprint requests to Dr. Mehboob A. Hussain, The two most popular chemicals for pharmacologic β cell ab-
Metabolism Division, Departments of Pediatrics, Medicine, and Biological lation are streptozotocin (STZ1) and alloxan (Elsner et al.
Chemistry, Johns Hopkins University, 600 N. Wolfe Street, CMSC 10-113,
Baltimore, MD 21287 or email mhussai4@gw.johnshopkins.edu.
2006). STZ, a nitrosourea analogue, decomposes into glucose
1Abbreviations used in this article: DM, diabetes mellitus; GLUT2, and a methylnitrosourea moiety that serves as an alkylating
glucose transporter 2; PPX, partial pancreatectomy; STZ, streptozotocin agent, which fragments DNA, modifies macromolecules,
74 ILAR Journaland results in the destruction of β cells. STZ also damages Differentiation of Pancreatic Duct Epithelium and Partial
mitochondrial function in part by alkylating and destroying Duct Ligation Studies provides details.
mitochondrial DNA, a result that is evident in reduced
glucose-stimulated insulin secretion and that also contributes
to β cell demise (Lenzen 2008). STZ administration does not Genetic Models of β Cell Ablation
prevent pancreas regeneration after partial pancreatectomy in
Concerns about the toxicity of STZ and alloxan to GLUT2-
rats (Finegood et al. 1999).
expressing cells that may be possible progenitors for β cell
Alloxan generates reactive oxygen species (ROS) in a cy-
regeneration have led to the creation of genetic models that
clic oxidation-reduction (redox) reaction in the presence of
allow targeted ablation of insulin-expressing cells only. One
intracellular thiols (e.g., glutathione). The resulting molecule
model is the PANIC-ATTAC2 transgenic mouse model, in
is dialuric acid, which via autooxidation generates superox-
which β cell–specific and dose-dependent pharmacological
ide radicals, hydrogen peroxide, and hydroxyl radicals. In ad-
activation of the cellular apoptosis cascade results in vari-
dition, alloxan inhibits glucokinase, which functions as the
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able degrees of β cell ablation (Wang et al. 2008). These
glucose sensor for the β cell, thereby suppressing glucose-
mice reveal in their islets a population of cells that express
stimulated insulin secretion (Lenzen 2008). Both STZ and
GLUT2 but not insulin, thus supporting the hypothesis that
alloxan are toxic glucose analogues that accumulate in pan-
GLUT2-positive, insulin-negative cells may represent a
creatic β cells after entering them via the glucose transporter
source for the formation of new functional β cells (Guz et al.
2 (GLUT21) (Elsner et al. 2002), which the cells express at
2001; Wang et al. 2008).
high levels. However, other cell types also express GLUT2
A second model of inducible β cell ablation is the β cell–
and the toxic effects of STZ on these cells have been a con-
specific conditional expression of diphtheria toxin A (DTA)
cern in regenerative studies. Other experimental paradigms
in genetically engineered mice (Nir et al. 2007). Mice do not
indicate the existence of an insulin-negative, GLUT2-positive
naturally express the diphtheria toxin receptor, thus protect-
cell population in the islets of Langerhans, which may pro-
ing all cells from DTA except those that express inducible
vide the cellular substrate for β cell regeneration (or matura-
DTA. In this model, replication (i.e., mitosis of existing, re-
tion) (Guz et al. 2001; Wang et al. 2008). These observations
sidual β cells) is the predominant if not sole mechanism of
are not mutually inconsistent. Rather, the different models
regeneration after partial β cell destruction (Nir et al. 2007).
may indicate the possibility of β cell regeneration from differ-
ent cell compartments of the pancreas, of which some cell
populations may actually be intermediary derivations from β Cell Proliferation Studies
other cell populations. For example, cells that give rise to β
cells in the partial pancreatectomy model (described in the Proliferation of β cells occurs during developmental forma-
next section) may actually start off as GLUT2-negative and tion of the pancreas and, in rodents, during the early postna-
thus be relatively protected from STZ; during the downstream tal period, concurrent with a wave of apoptosis and
process toward differentiation to β cells, the differentiating proliferation (Bonner-Weir 2000; Georgia and Bhushan
cells express GLUT2 and thus become vulnerable to STZ. 2004). In addition, functional adaptation of pancreatic β cells
to increasing insulin requirements, again in rodents, likely
Surgical Ablation of Pancreatic occurs primarily as a result of proliferation, the primary
Tissue (Partial Pancreatectomy) mechanism of β cell mass adaptation to metabolic demands.
Typical circumstances of increased insulin demand are diet-
Partial pancreatectomy (PPX1; removal of 60-90% of the induced insulin resistance and pregnancy, when the failure
pancreatic corpus and tail) in rodents is followed by a robust of β cell mass adaptation to metabolic demands results, re-
regeneration of pancreatic tissue, including the endocrine spectively, in impaired glucose tolerance or frank type 2 DM
compartment, that is complete approximately 2 weeks after and gestational DM.
the procedure (Bonner-Weir et al. 1993). Studies indicate Genomewide association studies have linked type 2 DM
that most if not all of the regenerating β cells derive from to single-nucleotide polymorphisms in genes, which are
proliferation of existing β cells (Dor et al. 2004). But careful highly expressed in β cells. The products of a number of
histological assessment has also revealed a proliferation of these identified genes are proteins, which regulate the cell
epithelial cells in small ductules in the pancreas, and these cycle (Saxena et al. 2007; Scott et al. 2007). Observations of
cells give rise to newly formed islets, pancreatic lobules, and β cell proliferation associated with increased metabolic de-
acinar tissue (Bonner-Weir et al. 1993). mands in rodents, combined with the genomewide associa-
Partial pancreatic duct ligation in rodents involves place- tion studies of type 2 DM, have led to the hypothesis that
ment of a stricture (usually across the middle or proximal type 2 DM in humans results in part from disturbed β cell
third of the pancreas) to obstruct the pancreatic duct, leaving mass adaptation (i.e., proliferation).
the vascular pancreatic perfusion intact. The ligation causes
the rapid atrophy of tissue distal to the ligation and the
proliferation of duct epithelium, which gives rise to newly 2PANIC-ATTAC stands for pancreatic islet β cell apoptosis through targeted
formed islets (neogenesis) and acinar tissue; the section on activation of caspase 8.
Volume 51, Number 1 2010 75β Cell Proliferation and Diet-Induced Obesity β cells have an equal capacity to proliferate (Brennand et al.
2007; Teta et al. 2007).
A robust model of increased peripheral and hepatic insulin
resistance entails a high-fat diet (60% of calories in the
form of lipids) for mice, which develop obesity and insulin Decline in β Cell Proliferation Capacity
resistance accompanied by β cell proliferation. Depending with Aging
on the strain of mice, either β cell proliferation is robust and
the animals do not develop diabetes, or proliferation is β cell proliferation is robust in young rodents (in mice up to
insufficient to meet metabolic demands and the animals approximately 2 months of age), but aging is accompanied
develop glucose intolerance and a type 2 DM phenotype. by diminished capacity of β cells to proliferate in response
Studies have exploited differences between mouse strains to various physiological, pharmacological, or experimental
to assess gene expression profiles in various tissues (Keller stimuli (Rankin and Kushner 2009; Tschen et al. 2009). Ge-
et al. 2008), with prominent differences in expression of netic studies of the restriction of β cell proliferation indicate
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cell cycle regulators in the islets of a mouse strain prone to a prominent role for the cell cycle negative regulatory pro-
developing diabetes with diet-induced obesity versus one teins encoded by the Ink4/Arf locus. Ablation of p16INK4a
that is not. results in preserved β cell regeneration after STZ-induced
partial β cell ablation in aging mice (Krishnamurthy et al.
2006). The Ink4/Arf locus is subject to epigenetic regulation
β Cell Mass Adaptation During Pregnancy by Polycomb proteins with age-related increased p16 ex-
pression and repression of β cell proliferation (Chen et al.
β cell mass adaptation during pregnancy occurs via β cell 2009; Dhawan et al. 2009).
proliferation. The current understanding is that during gesta- Given these observations, it is reasonable to expect that
tion placental lactogen and leptin, which are produced in young rodents may not reflect the circumstances of adult hu-
high quantities by the placenta, stimulate β cell proliferation. mans, in which β cell proliferation, although documented, is
Intracellular signaling for placental lactogen occurs via pro- rare and not as robust as in the early postnatal period (Butler
lactin receptors, which, together with leptin receptors, are et al. 2007b; Meier et al. 2008). In addition, studies combin-
expressed on β cells and stimulate the intracellular JAK2/ ing the immunohistochemistry of human cadaver pancreas
STAT signaling pathway. In the case of the prolactin recep- tissue and the mathematical modeling of β cell mass suggest
tor, JAK2/STAT5 signaling results in reduced expression of that in humans β cells form throughout adult life not from
the tumor suppressor menin (Festa et al. 1999; Freemark et al. the duplication of existing β cells but rather from as yet un-
2002; Huang et al. 2009; Karnik et al. 2005, 2007; Vasavada identified non-β cells (e.g., ductal epithelial cells, acinar
et al. 2000; Yamashita et al. 2001). cells, centroacinar cells, nonpancreas resident cells) (Saisho
Circulating serotonin levels increase and enzymes for et al. 2009).
serotonin synthesis are upregulated in mouse islets during
gestation (Kim et al. 2009; Schraenen et al. 2009). Impor-
tantly, inhibition of serotonin production by pharmacologic Transdifferentiation Studies
agents in pregnant mice as well as in β cell lines in vitro and Reprogramming
markedly reduces β cell proliferation (Kim et al. 2009). Thus
serotonin synthesis by β cells appears to be an important step To address circumstances when no β cells are present (e.g., in
in their adaptation during pregnancy. Further research is nec- long-standing type 1 diabetes) or existing β cells do not pro-
essary to determine how β cell serotonin is linked to the liferate (see above), researchers have tested the possibility of
stimulation of cell cycle progression. replacing β cells through the “transdifferentiation” of non-β
cells from a differentiated phenotype to a β cell phenotype
using a variety of cell sources. Among these are cells from
Methods of Inducing Cell Proliferation the pancreas (e.g., pancreatic duct epithelial cells or acinar
cells) or extrapancreatic tissue (e.g., liver, bone marrow). In
In addition to “physiological” circumstances of growth, diet-
the past 20 years, the discovery of β cell growth factors and
induced insulin resistance, and pregnancy, β cell prolifera-
transcription factors, which regulate pancreas and β cell de-
tion can be stimulated in rodents and observed after partial
velopment and differentiation, has provided important tools
ablation of β cell mass (i.e., through the administration of
for gene delivery and novel genetically engineered animal
alloxan, STZ, inducible apoptosis, or DTA expression) or
models that permit targeted investigation of the concept of
PPX (Dor et al. 2004). In addition, the incretin hormone
transdifferentiation of non-β cells to functional β cells.
glucagon-like peptide 1 (GLP-1) and its long-acting peptide
analogue exendin-4 stimulate β cell proliferation in rodents
via the GLP-1 receptor, which is expressed at high levels on Differentiation of Pancreatic Duct Epithelium
β cells (Song et al. 2008; Stoffers et al. 2000; Xu et al. 1999).
Studies that involve both the labeling of proliferating cells Pancreatic duct epithelium has long been considered to har-
and genetic lineage tracing indicate that in mouse models all bor cells with the capacity to differentiate into pancreatic
76 ILAR Journalendocrine cells under experimental circumstances. Rodent In vivo expression of a combination of developmentally
and human pancreatic duct epithelium can be cultured in important transcription factors (pdx-1, mafA, ngn3) in pan-
vitro and differentiated into islet-like structures that, after creatic acinar cells by adenovirus transduction results in a
transplantation, can reverse diabetes in a mouse lacking β reprogramming of acinar cells into insulin-secreting β cells
cells (Bonner-Weir et al. 2000, 2004, 2008; Hao et al. 2006; and rapid, sustained recovery from STZ-induced diabetes in
Inada et al. 2008). Studies combining genetic lineage tracing mice (Zhou et al. 2008). The reprogrammed cells exhibit ul-
of pancreatic duct epithelial cells with partial duct ligation trastructural features of pancreatic β cells and also attract
reveal the capacity for these cells to differentiate into pan- newly formed capillary blood vessels by expressing vascular
creatic acinar and endocrine cells (Bonner-Weir et al. 2008; endothelial growth factor (VEGF), which β cells have also
Inada et al. 2008). been shown to express (Zhou et al. 2008).
Additional studies indicate evidence of a subpopulation
of pancreatic duct epithelial cells that, after partial duct liga-
tion, express the developmental transcription factor neuro- β Cell Derivation from Liver Cells
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genin 3 (ngn3) and contribute to newly formed endocrine
The conversion of hepatocytes into pancreatic endocrine
cells. Neurogenin 3 is critical for pancreatic endocrine devel-
cells with reversal of STZ-induced diabetes in rodents has
opment, as shown by the complete lack of pancreatic endo-
been reported by several groups that have used similar strate-
crine cells in ngn3-null mice (Gradwohl et al. 2000) and the
gies of gene delivery and have reprogrammed hepatocytes to
lack of neogenesis of such cells after duct ligation (Xu et al.
β cell–like cells. The common feature in these studies is the
2008). A recent study demonstrated that pancreatic duct epi-
delivery of either the transcription factor pdx-1, alone or in
thelial cells differentiate into glucagon-expressing β cells
combination (Ber et al. 2003; Ferber et al. 2000) with beta-
(Collombat et al. 2009): when the paired homeodomain tran-
cellulin (Kojima et al. 2003), or a modified pdx-1 cDNA that
scription factor pax4 is misexpressed in the newly formed β
results in enhanced transcriptional activity of pdx-1 (Li et al.
cells, they differentiate into a β cell phenotype such that newly
2005a; Thowfeequ et al. 2009).
formed β cells functionally reverse chemically induced DM.
Researchers have recently shown that ngn3 transduction
In contrast, genetic lineage tracing studies in mice indi-
into liver cells results not only in transient expression of in-
cate that pancreatic endocrine regeneration after PPX occurs
sulin in hepatocytes but also, more importantly, in the emer-
primarily via proliferation of existing β cells (Dor et al.
gence of periportal clusters of islet-like cells that express
2004) and does not require reexpression of ngn3 (Lee et al.
phenotypic markers of islet cells, allowing for long-term re-
2006). These studies suggest differences between the mo-
versal of STZ-induced diabetes in mice (Yechoor et al.
lecular mechanisms underlying pancreatic endocrine cell
2009). The authors propose that progenitor cells in the peri-
(re)generation after PPX versus partial duct ligation, with
portal structures in the liver can, via ngn3 transduction, be
pancreatic duct epithelium cells possessing the capacity to
“transdetermined” to differentiation into pancreatic islet-like
reexpress ngn3 and possibly to recapitulate ontogenic steps
structures (Yechoor et al. 2009).
of pancreatic endocrine differentiation. When comparing re-
covery of β cell mass after specific experimental means of
reduction (β cell ablation, PPX, and pancreatic duct liga- Cells from Bone Marrow
tion), it appears that the different types of injury result in
recruitment of different cell types in the pancreas to regener- A small number of studies have reported the ability of bone
ate pancreatic endocrine mass. marrow–derived cells to differentiate into insulin-producing
cells after transplantation in animals (Hess et al. 2003; Ianus
et al. 2003; Wang et al. 2006). STZ diabetic mice that re-
Pancreatic Acinar Cells and Reprogramming ceived a transplant of a bone marrow–derived c-kit+ cell
population recovered from their diabetes. While a small frac-
The exocrine pancreatic acinar cells (Minami et al. 2005; tion (1-3%) of donor-derived cells are insulin-positive in the
Okuno et al. 2007) have been differentiated in vitro to pancre- pancreas, the main observation is that the transplantation
atic endocrine β cells through the overexpression of transcrip- procedure itself appears to stimulate host β cell proliferation,
tion factors, which are important for β cell differentiation and which is likely the main reason for the rapid recovery of host
phenotype maintenance (Li et al. 2005b; Wang et al. 2009). β cell mass and reversal of the diabetes phenotype (Hess et al.
In vivo delivery of pdx-1 and betacellulin (a peptidergic 2003). Other studies have failed to show evidence of bone
β cell differentiation factor) into the acinar tissue of STZ dia- marrow cell differentiation into pancreatic endocrine cells
betic rats, through transabdominal ultrasound-guided dis- (Akashi et al. 2008; Choi et al. 2003; Lechner et al. 2004).
ruption of the microvesicles (and from there into the In humans, maternal microchimerism (as a result of
circulation), permanently reverses the diabetes phenotype. maternal-to-fetal transfer of circulating blood cells during
Histological analysis indicates that the pancreatic acinar parturition) leads to female cells in male offspring. A recent
cells are converted into cells with certain characteristics of β study indicates that β cells with a female chromosomal com-
cells while acinar markers also remain detectable in these cells plement are present in male islets, suggesting the possibility
(Chen et al. 2007). of bloodborne cells, which under certain circumstances have
Volume 51, Number 1 2010 77the capacity to engraft islets and express a pancreatic endo- gies for improving iPS cell generation include replacing
crine phenotype (Nelson et al. 2007). In contrast, autopsy some if not all of the reprogramming transcription factors
studies of hematopoietic stem cell transplant recipients reveal with small molecular compounds and increasing the effi-
no evidence of pancreatic endocrine engraftment by donor ciency of iPS cell generation in an initial pool of cells
cells (Butler et al. 2007a). Nevertheless, clinical trials on the (Huangfu et al. 2008a,b). As with ESCs, it is important to
basis of these observations have reported a reversal of clinical address the possibility of teratoma formation, which is a
type 1 diabetes in humans after autologous treatment with property of iPS cells, before considering large-scale in vivo
bone marrow cell transplantation (Voltarelli et al. 2008). clinical applications.
These initial studies appear encouraging, but it remains iPS cells have been differentiated along lineages of a va-
unclear whether bone marrow harbors a cell type that may riety of tissue-specific phenotypes, include neuronal and car-
have the capacity to differentiate into a pancreatic endocrine diac phenotypes (Carey et al. 2009; Hanna et al. 2008;
cell phenotype. The lack of a mechanistic cellular and mo- Stadtfeld et al. 2008a). This variety opens the possibility of
lecular understanding of these observations certainly indi- generating disease-specific iPS cells that can be differenti-
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cates the need for further elucidation. ated for detailed in vitro studies (Park et al. 2008). A recent
report has described in vitro differentiation of insulin-
producing cells from human iPS cells (Zhang et al. 2009); so
Studies with Embryonic Stem Cells far, there are no reports of transplantation studies of iPS-
derived glucose-sensing and insulin-secreting cells.
Molecular mechanisms governing development of the pan-
creas and endocrine pancreas have provided insight and tools
for directed differentiation of human and mouse embryonic Islet and Islet-like Cell
stem cells (ESCs) to glucose-responsive insulin-producing Transplantation Studies
cells with close phenotypical resemblance to pancreatic β
In vitro–generated β cells, β cell surrogates, or islet-like
cells. Protocols for ESC-to-β cell differentiation have been
structures can be tested for their response to a glucose stimu-
developed by attempting to stimulate the signaling cascades
lus by in vitro exposure to various secretagogue stimuli, of
that govern embryonic β cell development and differentiation,
which glucose is the primary physiological stimulant. Static
resulting in recapitulation of the developmental transcription
incubation of β cell surrogates allows an assessment of dose-
signature of pancreas endocrine and β cell differentiation.
dependent secretion of insulin and C-peptide, both of which
A critical initial step is the differentiation into endoderm by
accumulate in the culture supernatant over time and can be
exposure of ESCs to the Activin A analogue Nodal. A step-
determined with a standard enzyme-linked immunosorbent
wise exposure to a variety of differentiation factors results
assay (ELISA). Dynamic response to secretagogues can be
in differentiation of cells toward a β cell phenotype
assessed by perifusion of islet-like structures and β cell sur-
(D’Amour et al. 2006; Kroon et al. 2008); recent reviews
rogates (perifusion involves the incubation of the test tissue
summarize protocols for differentiating ESCs into β cell
in a perifusion chamber, where the tissue is exposed to con-
phenotypes (Oliver-Krasinski and Stoffers 2008; Spence
trolled dynamic changes of secretagogues; dynamic changes
and Wells 2007).
in insulin and C-peptide can be measured in the effluent
Glucose-responsive insulin-secreting cells derived from
from the chamber) (Hussain et al. 2006).
ESCs have been tested in vivo after transplantation in dia-
Transplantation of insulin-producing cells, islets, and is-
betic mice. Although glucose metabolism can be satisfactorily
let-like structures permits in vivo assessment of the functional
controlled, the efficiency of successful ESC differentiation
performance of newly derived β cells. Before transplantation,
to β cells is low (approximately 10% of ESCs differentiate
syngeneic (to avoid immune rejection) or immunocompro-
into glucose-responsive cells) and potential teratoma forma-
mised recipient animals are rendered diabetic by β cell abla-
tion from ESC-derived tissue poses safety concerns for clini-
tion using STZ. Sites for transplantation include the peritoneal
cal application.
cavity, the portal vein (which introduces islets into the low-
pressure hepatic perfusion system), and a hollow space cre-
Studies with Induced Pluripotent Stem Cells ated between the kidney capsule and the kidney parenchyma.
The space under the kidney capsule is most commonly used
Induced pluripotent stem (iPS) cells were originally derived and provides a confined, accessible area for transplantation
from cultured mouse fibroblasts by stably or transiently over- while also permitting adequate blood and nutrient supply to
expressing three transcription factors (Oct4, Sox2, Klf4) the newly transplanted tissue. Depending on glucose sensing,
highly enriched in pluripotent ESCs (Stadtfeld et al. 2008b; insulin synthesis, and the secretion properties and capacity of
Takahashi and Yamanaka 2006; Yu et al. 2009). Other studies the transplanted tissue, glucose levels begin to decrease in the
with the same transcription factors enabled the generation of formerly diabetic transplant recipient. One advantage of
iPS cells from human fibroblasts (Takahashi et al. 2007) and transplantation under the kidney capsule is that after in vivo
the reprogramming of terminally differentiated somatic testing, the transplanted insulin-producing tissue can be re-
cells, including human β cells, to a pluripotent state (Carey moved to assess whether glucose levels return to diabetic lev-
et al. 2009; Hanna et al. 2008; Stadtfeld et al. 2008a). Strate- els in the surviving transplant host animal.
78 ILAR JournalIn an attempt to move toward allo- and xenotransplanta- extended liver to pancreas transdifferentiation. J Biol Chem 278:31950-
tion of glucose-responsive insulin-producing tissue across 31957.
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Concluding Remarks and Outlook
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RO1 DK 64646, RO1 DK 81472, RO1 DK 63349, RO1 DK
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