New opportunities: harnessing induced pluripotency for discovery in diabetes and metabolism

Advances in stem cells treatment of diabetic wounds: A bibliometric analysis via CiteSpace

Diabetes is a chronic medical condition that may induce complications such as poor wound healing. Stem cell therapies have shown promise in treating diabetic wounds with pre-clinical and clinical studies. However, little bibliometric analysis has been carried out on stem cells in the treatment of diabetic wounds. In this study, we retrieved relevant papers published from January 1, 2003, to December 31, 2023, from Chinese and English databases. CiteSpace software was used to analyze the authors, institutions, and keywords by standard bibliometric indicators. Our analysis findings indicated that publications on stem cells in the treatment of diabetic wounds kept increasing. The most prolific author was Qian Cai (n = 7) and Mohammad Bayat (n = 16) in Chinese and English databases, respectively. Institutions distribution analysis showed that Chinese institutions conducted most publications, and the most prolific institution was the Chinese People's Liberation Army General Hospital (n = 9) and Shahid Beheshti University of Medical Sciences (n = 17) in Chinese and English databases, respectively. The highest centrality keyword in Chinese and English databases was "wound healing" (0.54) and "in vitro" (0.13), respectively. There were 8 and 11 efficient and convincing keyword clusters produced by a log-likelihood ratio in the Chinese and English databases, respectively. The strongest burst keyword was "exosome" (strength 3.57) and "endothelial progenitor cells" (strength 7.87) in the Chinese and English databases, respectively. These findings indicated a direction for future therapies and research on stem cells in the treatment of diabetic wounds.

Innovations in Stem Cell Therapy for Diabetic Wound Healing

Significance: The global burden of diabetic wounds, particularly diabetic foot ulcers, continues to have large economic and social impact throughout the world. Current strategies are not sufficient to overcome this burden of disease. Finding newer, more advanced regenerative cell and tissue-based strategies to reduce morbidity remains paramount. Recent Advances: Recent advances in stem cell therapies are discussed. We also highlight the practical issues of translating these advancing technologies into the clinical setting. Critical Issues: We discuss the use of somatic and induced pluripotent stem cells and the stromal vascular fraction, as well as innovations, including the use of 3D bioprinting of skin. We also explore related issues of using regenerative techniques in clinical practice, including the current regulatory landscape and translatability of in vivo research. Future Directions: Advances in stem cell manipulation showcase the best therapeutic resources available to enhance mechanisms of wound healing such as angiogenesis, cell proliferation, and collagen synthesis; potential methods include changing the scaffold microenvironment, including relative oxygen tension, and the use of gene modification and nanotechnology. Secretome engineering, particularly the use of extracellular vesicles, may be another potential cell-derived therapeutic that may enable use of cell-free translational therapy.

PAX4 loss of function increases diabetes risk by altering human pancreatic endocrine cell development

The coding variant (p.Arg192His) in the transcription factor PAX4 is associated with an altered risk for type 2 diabetes (T2D) in East Asian populations. In mice, Pax4 is essential for beta cell formation but its role on human beta cell development and/or function is unknown. Participants carrying the PAX4 p.His192 allele exhibited decreased pancreatic beta cell function compared to homozygotes for the p.192Arg allele in a cross-sectional study in which we carried out an intravenous glucose tolerance test and an oral glucose tolerance test. In a pedigree of a patient with young onset diabetes, several members carry a newly identified p.Tyr186X allele. In the human beta cell model, EndoC-βH1, PAX4 knockdown led to impaired insulin secretion, reduced total insulin content, and altered hormone gene expression. Deletion of PAX4 in human induced pluripotent stem cell (hiPSC)-derived islet-like cells resulted in derepression of alpha cell gene expression. In vitro differentiation of hiPSCs carrying PAX4 p.His192 and p.X186 risk alleles exhibited increased polyhormonal endocrine cell formation and reduced insulin content that can be reversed with gene correction. Together, we demonstrate the role of PAX4 in human endocrine cell development, beta cell function, and its contribution to T2D-risk.

m 6 A mRNA Methylation Regulates Early Pancreatic β-Cell Differentiation

N 6 -methyladenosine (m 6 A) is the most abundant chemical modification in mRNA, and plays important roles in human and mouse embryonic stem cell pluripotency, maintenance, and differentiation. We have recently reported, for the first time, the role of m 6 A in the postnatal control of β-cell function in physiological states and in Type 1 and 2 Diabetes. However, the precise mechanisms by which m 6 A acts to regulate the development of human and mouse β-cells are unexplored. Here, we show that the m 6 A landscape is dynamic during human pancreas development, and that METTL14, one of the m 6 A writer complex proteins, is essential for the early differentiation of both human and mouse β-cells.

Harnessing Human Pluripotent Stem Cell-Derived Pancreatic In Vitro Models for High-Throughput Toxicity Testing and Diabetes Drug Discovery

The long-standing goals in diabetes research are to improve β-cell survival, functionality and increase β-cell mass. Current strategies to manage diabetes progression are still not ideal for sustained maintenance of normoglycemia, thereby increasing demand for the development of novel drugs. Available pancreatic cell lines, cadaveric islets, and their culture methods and formats, either 2D or 3D, allow for multiple avenues of experimental design to address diverse aims in the research setting. More specifically, these pancreatic cells have been employed in toxicity testing, diabetes drug screens, and with careful curation, can be optimized for use in efficient high-throughput screenings (HTS). This has since spearheaded the understanding of disease progression and related mechanisms, as well as the discovery of potential drug candidates which could be the cornerstone for diabetes treatment. This book chapter will touch on the pros and cons of the most widely used pancreatic cells, including the more recent human pluripotent stem cell-derived pancreatic cells, and HTS strategies (cell models, design, readouts) that can be used for the purpose of toxicity testing and diabetes drug discovery.

Multidisciplinary Effort to Drive Precision-Medicine for the Future

In the past one or two decades, countries across the world have successively implemented different precision medicine (PM) programs, and also cooperated to implement international PM programs. We are now in the era of PM. Singapore's National Precision Medicine (NPM) program, initiated in 2017, is now entering its second phase to generate a large genomic database for Asians. The National University of Singapore (NUS) also launched its own PM translational research program (TRP) in 2021, aimed at consolidating multidisciplinary expertise within the Yong Loo Lin School of Medicine to develop collaborative projects that can help to identify and validate novel therapeutic targets for the realization of PM. To achieve this, appropriate data collection, data processing, and results interpretation must be taken into consideration. There may be some difficulties during these processes, but with the improvement of relevant rules and the continuous development of omics-based technologies, we will be able to solve these problems, eventually achieving precise prediction, diagnosis, treatment, or even prevention of diseases.

Human expandable pancreatic progenitor-derived β cells ameliorate diabetes

An unlimited source of human pancreatic β cells is in high demand. Even with recent advances in pancreatic differentiation from human pluripotent stem cells, major hurdles remain in large-scale and cost-effective production of functional β cells. Here, through chemical screening, we demonstrate that the bromodomain and extraterminal domain (BET) inhibitor I-BET151 can robustly promote the expansion of PDX1⁺NKX6.1⁺ pancreatic progenitors (PPs). These expandable PPs (ePPs) maintain pancreatic progenitor cell status in the long term and can efficiently differentiate into functional pancreatic β (ePP-β) cells. Notably, transplantation of ePP-β cells rapidly ameliorated diabetes in mice, suggesting strong potential for cell replacement therapy. Mechanistically, I-BET151 activates Notch signaling and promotes the expression of key PP-associated genes, underscoring the importance of epigenetic and transcriptional modulations for lineage-specific progenitor self-renewal. In summary, our studies achieve the long-term goal of robust expansion of PPs and represent a substantial step toward unlimited supplies of functional β cells for biomedical research and regenerative medicine.

Genome Editing and Human Pluripotent Stem Cell Technologies for in vitro Monogenic Diabetes Modeling

Diabetes is a metabolic disease characterized by chronic hyperglycemia. Polygenic diabetes, which encompasses type-1 and type-2 diabetes, is the most prevalent kind of diabetes and is caused by a combination of different genetic and environmental factors, whereas rare phenotype monogenic diabetes is caused by a single gene mutation. Monogenic diabetes includes Neonatal diabetes mellitus and Maturity-onset diabetes of the young. The majority of our current knowledge about the pathogenesis of diabetes stems from studies done on animal models. However, the genetic difference between these creatures and humans makes it difficult to mimic human clinical pathophysiology, limiting their value in modeling key aspects of human disease. Human pluripotent stem cell technologies combined with genome editing techniques have been shown to be better alternatives for creating in vitro models that can provide crucial knowledge about disease etiology. This review paper addresses genome editing and human pluripotent stem cell technologies for in vitro monogenic diabetes modeling.

Recent advances and potential applications of human pluripotent stem cell-derived pancreatic β cells

Diabetes mellitus is characterized by chronic high blood glucose levels resulted from deficiency and/or dysfunction of insulin-producing pancreatic β cells. Generation of large amounts of functional pancreatic β cells is critical for the study of pancreatic biology and treatment of diabetes. Recent advances in directed differentiation of pancreatic β-like cells from human pluripotent stem cells (hPSCs) can provide patient-specific and disease-relevant target cells. With the improved differentiation protocols, it is now possible to generate large amounts of functional human pancreatic β-like cells that can response to high level of glucose both in vitro and in vivo. Combined with precise genomic editing, biomedical engineering, high throughput profiling, bioinformatics, and high throughput genetic and chemical screening, these hPSC-derived pancreatic β-like cells will hold great potentials in disease modeling, drug discovery, and cell-based therapies. In this review, we summarize the recent progress in human pancreatic β-like cells derived from hPSCs and discuss their potential applications.

BCL-xL/BCL2L1 is a critical anti-apoptotic protein that promotes the survival of differentiating pancreatic cells from human pluripotent stem cells

The differentiation of human pluripotent stem cells into pancreatic cells involves cellular proliferation and apoptosis during cell fate transitions. However, their implications for establishing cellular identity are unclear. Here, we profiled the expression of BCL-2 family of proteins during pancreatic specification and observed an upregulation of BCL-xL, downregulation of BAK and corresponding downregulation of cleaved CASP3 representative of apoptosis. Experimental inhibition of BCL-xL reciprocally increased apoptosis and resulted in a decreased gene expression of pancreatic markers despite a compensatory increase in anti-apoptotic protein BCL-2. RNA-Seq analyses then revealed a downregulation of multiple metabolic genes upon inhibition of BCL-xL. Follow-up bioenergetics assays revealed broad downregulation of both glycolysis and oxidative phosphorylation when BCL-xL was inhibited. Early perturbation of BCL-xL during pancreatic specification also had subsequent detrimental effects on the formation of INS⁺ pancreatic beta-like cells. In conclusion, the more differentiated pancreatic progenitors are dependent on anti-apoptotic BCL-xL for survival, whereas the less differentiated pancreatic progenitors that survived after WEHI-539 treatment would exhibit a more immature phenotype. Therefore, modulation of the expression level of BCL-xL can potentially increase the survival and robustness of pancreatic progenitors that ultimately define human pancreatic beta cell mass and function.

Cell therapy for type 1 diabetes

INTRODUCTION

Type 1 diabetes (T1D) is a lifelong condition resulting from autoimmune destruction of insulin-producing β-cells. Islet or whole-pancreas transplantation is limited by the shortage of donors and need for chronic immune suppression. Novel strategies are needed to prevent β-cell loss and to rescue production of endogenous insulin.

AREAS COVERED

This review covers the latest advances in cell-based therapies for the treatment and prevention of T1D. Topics include adoptive transfer of cells with increased immunoregulatory potential for β-cell protection, and β-cell replacement strategies such as generation of insulin-producing β-like cells from unlimited sources.

EXPERT OPINION

Cell therapy provides an opportunity to prevent or reverse T1D. Adoptive transfer of autologous cells having enhanced immunomodulatory properties can suppress autoimmunity and preserve β-cells. Such therapies have been made possible by a combination of genome-editing techniques and transplantation of tolerogenic cells. In-vitro modified autologous hematopoietic stem cells and tolerogenic dendritic cells may protect endogenous and newly generated β-cells from a patient's autoimmune response without hampering immune surveillance for infectious agents and malignant cellular transformations. However, methods to generate cells that meet quality and safety standards for clinical applications require further refinement.

Dynamic proteome profiling of human pluripotent stem cell-derived pancreatic progenitors

A comprehensive characterization of the molecular processes controlling cell fate decisions is essential to derive stable progenitors and terminally differentiated cells that are functional from human pluripotent stem cells (hPSCs). Here, we report the use of quantitative proteomics to describe early proteome adaptations during hPSC differentiation toward pancreatic progenitors. We report that the use of unbiased quantitative proteomics allows the simultaneous profiling of numerous proteins at multiple time points, and is a valuable tool to guide the discovery of signaling events and molecular signatures underlying cellular differentiation. We also monitored the activity level of pathways whose roles are pivotal in the early pancreas differentiation, including the Hippo signaling pathway. The quantitative proteomics data set provides insights into the dynamics of the global proteome during the transition of hPSCs from a pluripotent state toward pancreatic differentiation.

Tools for Bioimaging Pancreatic β Cells in Diabetes

When diabetes is diagnosed, the majority of insulin-secreting pancreatic β cells are already dysfunctional or destroyed. This β cell dysfunction/destruction usually takes place over many years, making timely detection and clinical intervention difficult. For this reason, there is immense interest in developing tools to bioimage β cell mass and/or function noninvasively to facilitate early diagnosis of diabetes as well as to assist the development of novel antidiabetic therapies. Recent years have brought significant progress in β cell imaging that is now inching towards clinical applicability. We explore here the need to bioimage human β cells noninvasively in various types of diabetes, and we discuss current and emerging tools for bioimaging β cells. Further developments in this field are expected to facilitate β cell imaging in diabetes.

HNF4A Haploinsufficiency in MODY1 Abrogates Liver and Pancreas Differentiation from Patient-Derived Induced Pluripotent Stem Cells

Maturity-onset diabetes of the young 1 (MODY1) is a monogenic diabetes condition caused by heterozygous HNF4A mutations. We investigate how HNF4A haploinsufficiency from a MODY1/HNF4A mutation influences the development of foregut-derived liver and pancreatic cells through differentiation of human induced pluripotent stem cells from a MODY1 family down the foregut lineage. In MODY1-derived hepatopancreatic progenitors, which expressed reduced HNF4A levels and mislocalized HNF4A, foregut genes were downregulated, whereas hindgut-specifying HOX genes were upregulated. MODY1-derived hepatocyte-like cells were found to exhibit altered morphology. Hepatic and β cell gene signatures were also perturbed in MODY1-derived hepatocyte-like and β-like cells, respectively. As mutant HNF4A (p.Ile271fs) did not undergo complete nonsense-mediated decay or exert dominant negativity, HNF4A-mediated loss of function is likely due to impaired transcriptional activation of target genes. Our results suggest that in MODY1, liver and pancreas development is perturbed early on, contributing to altered hepatic proteins and β cell defects in patients.

•

HNF4A is downregulated and predominantly mislocalized in the cytoplasm in MODY1

•

Foregut markers, pancreatic and hepatic genes, were downregulated in MODY1-HPPs

•

A reciprocal upregulation of hindgut HOX genes was observed in MODY1-HPPs

•

Mutant HNF4A resulted in loss of transcriptional activation of target genes

Concise Review: Human Pluripotent Stem Cells for the Modeling of Pancreatic β-Cell Pathology

Pancreatic β‐cells are the only source of insulin. Disturbances in β‐cell development or function may thus result in insulin deficiency or excess, presenting as hyper‐ or hypoglycemia. It is increasingly evident that common forms of diabetes (types 1 and 2) are pathogenically heterogeneous. Development of efficient therapies is dependent on reliable disease models. Although animal models are remarkably useful research tools, they present limitations because of species differences. As an alternative, human pluripotent stem cell technologies offer multiple possibilities for the study of human diseases in vitro. In the last decade, advances in the derivation of induced pluripotent stem cells from diabetic patients, combined with β‐cell differentiation protocols, have resulted in the generation of useful disease models for diabetes. First disease models have been focusing on monogenic diabetes. The development of genome editing technologies, more advanced differentiation protocols and humanized mouse models based on transplanted cells have opened new horizons for the modeling of more complex forms of β‐cell dysfunction. We present here the incremental progress made in the modeling of diabetes using pluripotent stem cells. We discuss the current challenges and opportunities of these approaches to dissect β‐cell pathology and devise new pharmacological and cell replacement therapies. stem cells2019;37:33–41

Derivation and molecular characterization of pancreatic differentiated MODY1-iPSCs

Maturity onset diabetes of the young (MODY) is a hereditary form of diabetes mellitus presenting at childhood or adolescence, which eventually leads to pancreatic β-cells dysfunction. The underlying genetic basis of MODY disorders is haploinsufficiency, where loss-of-function mutations in a single allele cause the diabetic phenotype in heterozygous patients. MODY1 is a type of MODY disorder resulting from a mutation in the transcription factor hepatocyte nuclear factor 4 alpha (HNF4α). In order to establish a human based model to study MODY1, we generated patient-derived induced pluripotent stem cells (iPSCs). Differentiation of these pluripotent cells towards the pancreatic lineage enabled to evaluate the effects of the MODY1 mutation and its impact on endodermal and pancreatic cells. Analyzing the gene expression profiles of differentiated MODY1 cells, revealed the outcome of HNF4α haploinsufficiency on its targets. This molecular analysis suggests that the differential expression of HNF4α target genes in MODY1 is affected by the number of HNF4α binding sites, their distance from the transcription start site, and the number of other transcription factor binding sites. These features may help explain the molecular manifestations of haploinsufficiency in MODY1 disease.

Human Induced Pluripotent Stem Cells in the Curative Treatment of Diabetes and Potential Impediments Ahead

The successful landmark discovery of mouse and human inducible pluripotential stem cells (iPSC's) by Takahashi and Yamanaka in 2006 and 2007 has triggered a revolution in the potential generation of self-compatible cells for regenerative medicine, and further opened up a new avenue for "disease in dish" drug screening of self-target cells (Neofytou et al. 2015). The introduction of four 'Yamanaka' transcription factors through viral or other transfection of mature cells can induce pluripotency and acquired plasticity. These factors include transduction with octamer-binding transcription factor-4 (Oct-4), nanog homeobox (Nanog), sex-determining region Y-box-2 (Sox-2) and MYC protooncogene (cMyc). Such cells become iPSC's (Takahashi and Yamanaka 2006). These reprogrammed cells exhibit increased telomerase activity and have a hypomethylated gene promotor region similar to embryonic stem cells (ESC's). These milestone discoveries have generated immense hope that diseases such as diabetes could be treated and effectively cured by transplantation of self-compatible, personalized autologous stem cell transplantation of β-cells that release physiological insulin under glycemic control (Maehr et al. 2009; Park et al. 2008) (Fig. 1). Diabetes is a profligate disease of disordered glucose metabolism resulting from an absolute or relative deficiency of insulin, the consequences of which lead to immense socio-economic societal burden. While there are many different types of diabetes, the two major types (type 1 diabetes (T1DM) and type 2 diabetes (T2DM) are caused respectively by immune-mediated destruction (T1DM) or malfunctioning (T2DM) insulin-producing β-cells within the endocrine pancreas, the islets of Langerhans (Atkinson et al. 2011; Holman et al. 2015; You and Henneberg 2016). Almost 425 million people are affected by the global burden of diabetes, and this is predicted to increase by 48% (629 million) by 2045 (International Diabetes Federation Atlas 8th Ed 2018). Whole pancreas or islet cell transplantation offer an effective alternative to injected insulin, but both require lifelong potent immunosuppression to control both allo-and autoimmunity. Whole pancreas transplantation involves invasive complex surgery and is associated with greater morbidity and occasional mortality, while islet transplantation involves a minimally invasive intraportal hepatic infusion. Generally, whole pancreas transplantation provides greater metabolic reserve, but this may be matched by cumulative multiple islet infusions to achieve insulin independence. An additional challenge of islet transplantation is progressive loss of complete insulin independence over time, which may be multifactorial, the dominant factor however being ineffective control of autoimmunity. Both whole pancreas and islet transplantation are restricted to patients at risk of severe hypoglycemia that cannot be stabilized by alternate means, or in recipients that are already immunosuppressed in order to sustain a kidney or other solid organ transplant. The risks of chronic immunosuppression and the scarcity of human organ donors mean that both of these transplantation therapies cannot presently be extended to the broader diabetic population (Shapiro 2011; Shapiro et al. 2006). Recent progress in xenotransplantation of multiple knock-out 'humanized' pig islets could offer one potential solution, perhaps aided by clustered regularly interspaced short palindromic repeats/CRISPR associated-9 (CRISPR/Cas-9) gene editing approaches, but this remains to be proven in practice. Human stem cell derived new β-cell products could effectively address the global supply challenge for broad application across all forms of diabetes, but recurrent autoimmunity may still remain an insurmountable challenge. Considerable progress in the generation of human stem cell derived SC-β cells from ESC, iPS and other adult cell sources such as mesenchymal stem cells (MSCs) offer huge hope that a personalized, 'syngeneic' cell could be transplanted without risk of alloimmunity, thereby securing sufficient supply to meet future global demand (Cito et al. 2018).

An arduous journey from human pluripotent stem cells to functional pancreatic β cells

Type 1 and type 2 diabetes are caused by a destruction and decrease in the number of functional insulin-producing β cells, respectively; therefore, the generation of functional β cells from human embryonic stem cells and human induced pluripotent stem cells, collectively known as human pluripotent stem cells (hPSCs), for potential cell replacement therapy and disease modelling is an intensely investigated area. Recent scientific breakthroughs enabled derivation of large quantities of human pancreatic β-like cells in vitro, although with varied glucose-stimulated insulin secretion kinetics. In the present review, we comprehensively summarize, compare and critically analyze the intricacies of these developing technologies, including differentiation platforms, robustness of protocols, and methodologies used to characterize hPSC-derived β-like cells. We also discuss experimental issues that need to be resolved before these β-like cells can be used clinically.

Reactivation of hyperglycemia-induced hypocretin (HCRT) gene silencing by N-acetyl-d-mannosamine in the orexin neurons derived from human iPS cells

Orexin neurons regulate critical brain activities for controlling sleep, eating, emotions, and metabolism, and impaired orexin neuron function results in several neurologic disorders. Therefore, restoring normal orexin function and understanding the mechanisms of loss or impairment of orexin neurons represent important goals. As a step toward that end, we generated human orexin neurons from induced pluripotent stem cells (hiPSCs) by treatment with N-acetyl-d-mannosamine (ManNAc) and its derivatives. The generation of orexin neurons was associated with DNA hypomethylation, histone H3/H4 hyperacetylation, and hypo-O-GlcNAcylation on the HCRT gene locus, and, thereby, the treatment of inhibitors of SIRT1 and OGT were effective at inducing orexin neurons from hiPSCs. The prolonged exposure of orexin neurons to high glucose in culture caused irreversible silencing of the HCRT gene, which was characterized by H3/H4 hypoacetylation and hyper-O-GlcNAcylation. The DNA hypomethylation status, once established in orexin neurogenesis, was maintained in the HCRT-silenced orexin neurons, indicating that histone modifications, but not DNA methylation, were responsible for the HCRT silencing. Thus, the epigenetic status of the HCRT gene is unique to the hyperglycemia-induced silencing. Intriguingly, treatment of ManNAc and its derivatives reactivated HCRT gene expression, while inhibitors SIRT1 and the OGT did not. The present study revealed that the HCRT gene was silenced by the hyperglycemia condition, and ManNAc and its derivatives were useful for restoring the orexin neurons.

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.

The role of hepatocyte nuclear factor 1β in disease and development

Heterozygous mutations in the gene that encodes the transcription factor hepatocyte nuclear factor 1β (HNF1B) result in a multi-system disorder. HNF1B was initially discovered as a monogenic diabetes gene; however, renal cysts are the most frequently detected feature. Other clinical features include pancreatic hypoplasia and exocrine insufficiency, genital tract malformations, abnormal liver function, cholestasis and early-onset gout. Heterozygous mutations and complete gene deletions in HNF1B each account for approximately 50% of all cases of HNF1B-associated disease and may show autosomal dominant inheritance or arise spontaneously. There is no clear genotype-phenotype correlation indicating that haploinsufficiency is the main disease mechanism. Data from animal models suggest that HNF1B is essential for several stages of pancreas and liver development. However, mice with heterozygous mutations in HNF1B show no phenotype in contrast to the phenotype seen in humans. This suggests that mouse models do not fully replicate the features of human disease and complementary studies in human systems are necessary to determine the molecular mechanisms underlying HNF1B-associated disease. This review discusses the role of HNF1B in human and murine pancreas and liver development, summarizes the disease phenotypes and identifies areas for future investigations in HNF1B-associated diabetes and liver disease.

Vascular diseases await translation of blood vessels engineered from stem cells

The discovery of human induced pluripotent stem cells (hiPSCs) might pave the way toward a long-sought solution for obtaining sufficient numbers of autologous cells for tissue engineering. Several methods exist for generating endothelial cells or perivascular cells from hiPSCs in vitro for use in the building of vascular tissue. We discuss current developments in the generation of vascular progenitor cells from hiPSCs and the assessment of their functional capacity in vivo, opportunities and challenges for the clinical translation of engineered vascular tissue, and modeling of vascular diseases using hiPSC-derived vascular progenitor cells.

Engineering pancreatic tissues from stem cells towards therapy

Pancreatic islet transplantation is performed as a potential treatment for type 1 diabetes mellitus. However, this approach is significantly limited due to the critical shortage of islet sources. Recently, a number of publications have developed protocols for directed β-cell differentiation of pluripotent cells, such as embryonic stem (ES) or induced pluripotent stem (iPS) cells. Decades of studies have led to the development of modified protocols that recapitulate molecular developmental cues by combining various growth factors and small molecules with improved efficiency. However, the later step of pancreatic differentiation into functional β-cells has yet to be satisfactory in vitro, highlighting alternative approach by recapitulating spatiotemporal multicellular interaction in three-dimensional (3D) culture. Here, we summarize recent progress in the directed differentiation into pancreatic β-cells with a focus on both two-dimensional (2D) and 3D differentiation settings. We also discuss the potential transplantation strategies in combination with current bioengineering approaches towards diabetes therapy.

•

Transplantation of stem cell derived pancreatic progenitors is a possible approach for generating mature β-cell in vivo.

•

Promise of 3-D (or 4-D) culture has started to be explored by reconstituting pancreatic tissue structures.

•

Self-condensation culture is a basic technique of integrating multiple heterotypic lineages including vasculatures.

•

Bioengineering approach has been combined for developing effective transplant strategies.

Early Developmental Perturbations in a Human Stem Cell Model of MODY5/HNF1B Pancreatic Hypoplasia

Patients with an HNF1B^S148L/+ mutation (MODY5) typically exhibit pancreatic hypoplasia. However, the molecular mechanisms are unknown due to inaccessibility of patient material and because mouse models do not fully recapitulate MODY5. Here, we differentiated MODY5 human-induced pluripotent stem cells (hiPSCs) into pancreatic progenitors, and show that the HNF1B^S148L/+ mutation causes a compensatory increase in several pancreatic transcription factors, and surprisingly, a decrease in PAX6 pancreatic gene expression. The lack of suppression of PDX1, PTF1A, GATA4, and GATA6 indicates that MODY5-mediated pancreatic hypoplasia is mechanistically independent. Overexpression studies demonstrate that a compensatory increase in PDX1 gene expression is due to mutant HNF1B^S148L/+ but not wild-type HNF1B or HNF1A. Furthermore, HNF1B does not appear to directly regulate PAX6 gene expression necessary for glucose tolerance. Our results demonstrate compensatory mechanisms in the pancreatic transcription factor network due to mutant HNF1B^S148L/+ protein. Thus, patients typically develop MODY5 but not neonatal diabetes despite exhibiting pancreatic hypoplasia.

•

HNF1B^S148L/+ mutation elicits a compensatory increase in DE and pancreatic genes

•

MODY5-mediated pancreatic hypoplasia is independent of PDX1, PTF1A, GATA4, and GATA6

•

HNF1B^S148L mutation directly causes a compensatory increase in PDX1 gene expression

•

HNF1B^S148L/+ mutation limits PAX6 expression and consequently leads to MODY5

Proceedings: consideration of genetics in the design of induced pluripotent stem cell-based models of complex disease

The goal of exploiting induced pluripotent stem cell (iPSC) technology for the discovery of new mechanisms and treatments of disease is being pursued by many laboratories, and analyses of rare monogenic diseases have already provided ample evidence that this approach has merit. Considering the enormous medical burden imposed by common chronic diseases, successful implementation of iPSC-based models has the potential for major impact on these diseases as well. Since common diseases represent complex traits with varying genetic and environmental contributions to disease manifestation, the use of iPSC technology poses unique challenges. In this perspective, we will consider how the genetics of complex disease and mechanisms underlying phenotypic variation affect experimental design.

Dissecting diabetes/metabolic disease mechanisms using pluripotent stem cells and genome editing tools

BACKGROUND

Diabetes and metabolic syndromes are chronic, devastating diseases with increasing prevalence. Human pluripotent stem cells are gaining popularity in their usage for human in vitro disease modeling. With recent rapid advances in genome editing tools, these cells can now be genetically manipulated with relative ease to study how genes and gene variants contribute to diabetes and metabolic syndromes.

SCOPE OF REVIEW

We highlight the diabetes and metabolic genes and gene variants, which could potentially be studied, using two powerful technologies - human pluripotent stem cells (hPSCs) and genome editing tools - to aid the elucidation of yet elusive mechanisms underlying these complex diseases.

MAJOR CONCLUSIONS

hPSCs and the advancing genome editing tools appear to be a timely and potent combination for probing molecular mechanism(s) underlying diseases such as diabetes and metabolic syndromes. The knowledge gained from these hiPSC-based disease modeling studies can potentially be translated into the clinics by guiding clinicians on the appropriate type of medication to use for each condition based on the mechanism of action of the disease.

Cellular therapies based on stem cells and their insulin-producing surrogates: a 2015 reality check

Stem cell technology has recently gained a substantial amount of interest as one method to create a potentially limitless supply of transplantable insulin-producing cells to treat, and possibly cure diabetes mellitus. In this review, we summarize the state-of-the art of stem cell technology and list the potential sources of stem cells that have been shown to be useful as insulin-expressing surrogates. We also discuss the milestones that have been reached and those that remain to be addressed to generate bona fide beta cell-similar, insulin-producing surrogates. The caveats, limitations, and realistic expectations are also considered for current and future technology. In spite of the tremendous technical advances realized in the past decade, especially in the field of reprogramming adult somatic cells to become stem cells, the state-of-the art still relies on lengthy and cumbersome in vitro culture methods that yield cell populations that are not particularly glucose-responsive when transplanted into diabetic hosts. Despite the current impediments toward clinical translation, including the potential for immune rejection, the availability of technology to generate patient-specific reprogrammable stem cells has, and will be critical for, important insights into the genetics, epigenetics, biology, and physiology of insulin-producing cells in normal and pathologic states. This knowledge could accelerate the time to reach the desired breakthrough for safe and efficacious beta cell surrogates.

Stem cells for the cell and molecular therapy of type 1 diabetes mellitus (T1D): the gap between dream and reality

In spite of intense research, over the past 2-3 decades, targeted to validating methods for the cure of T1D, based on cell substitution therapy in the place of exogenously administered insulin injections, achievement of the final goal continues to remain out of reach. In fact, aside of very limited clinical success of the few clinical trials of pancreatic islet cell transplantation in totally immunosuppressed patients with T1D, the vast majority of these diabetic patients invariably is insulin-dependent. New advances for cell and molecular therapy for T1D, including use of stem cells, are reviewed and discussed in an attempt to clearly establish where we are and where are we may go for the final cure for T1DM.

Advances and challenges in the differentiation of pluripotent stem cells into pancreatic β cells

Pluripotent stem cells (PSCs) are able to differentiate into several cell types, including pancreatic β cells. Differentiation of pancreatic β cells depends on certain transcription factors, which function in a coordinated way during pancreas development. The existing protocols for in vitro differentiation produce pancreatic β cells, which are not highly responsive to glucose stimulation except after their transplantation into immune-compromised mice and allowing several weeks for further differentiation to ensure the maturation of these cells in vivo. Thus, although the substantial improvement that has been made for the differentiation of induced PSCs and embryonic stem cells toward pancreatic β cells, several challenges still hindering their full generation. Here, we summarize recent advances in the differentiation of PSCs into pancreatic β cells and discuss the challenges facing their differentiation as well as the different applications of these potential PSC-derived β cells.

Knowledge Gaps in Rodent Pancreas Biology: Taking Human Pluripotent Stem Cell-Derived Pancreatic Beta Cells into Our Own Hands

In the field of stem cell biology and diabetes, we and others seek to derive mature and functional human pancreatic β cells for disease modeling and cell replacement therapy. Traditionally, knowledge gathered from rodents is extended to human pancreas developmental biology research involving human pluripotent stem cells (hPSCs). While much has been learnt from rodent pancreas biology in the early steps toward Pdx1(+) pancreatic progenitors, much less is known about the transition toward Ngn3(+) pancreatic endocrine progenitors. Essentially, the later steps of pancreatic β cell development and maturation remain elusive to date. As a result, the most recent advances in the stem cell and diabetes field have relied upon combinatorial testing of numerous growth factors and chemical compounds in an arbitrary trial-and-error fashion to derive mature and functional human pancreatic β cells from hPSCs. Although this hit-or-miss approach appears to have made some headway in maturing human pancreatic β cells in vitro, its underlying biology is vaguely understood. Therefore, in this mini-review, we discuss some of these late-stage signaling pathways that are involved in human pancreatic β cell differentiation and highlight our current understanding of their relevance in rodent pancreas biology. Our efforts here unravel several novel signaling pathways that can be further studied to shed light on unexplored aspects of rodent pancreas biology. New investigations into these signaling pathways are expected to advance our knowledge in human pancreas developmental biology and to aid in the translation of stem cell biology in the context of diabetes treatments.

Pluripotent stem cells as a potential tool for disease modelling and cell therapy in diabetes

Diabetes mellitus is the most prevailing disease with progressive incidence worldwide. To date, the pathogenesis of diabetes is far to be understood, and there is no permanent treatment available for diabetes. One of the promising approaches to understand and cure diabetes is to use pluripotent stem cells (PSCs), including embryonic stem cells (ESCs) and induced PCSs (iPSCs). ESCs and iPSCs have a great potential to differentiate into all cell types, and they have a high ability to differentiate into insulin-secreting β cells. Obtaining PSCs genetically identical to the patient presenting with diabetes has been a longstanding dream for the in vitro modeling of disease and ultimately cell therapy. For several years, somatic cell nuclear transfer (SCNT) was the method of choice to generate patient-specific ESC lines. However, this technology faces ethical and practical concerns. Interestingly, the recently established iPSC technology overcomes the major problems of other stem cell types including the lack of ethical concern and no risk of immune rejection. Several iPSC lines have been recently generated from patients with different types of diabetes, and most of these cell lines are able to differentiate into insulin-secreting β cells. In this review, we summarize recent advances in the differentiation of pancreatic β cells from PSCs, and describe the challenges for their clinical use in diabetes cell therapy. Furthermore, we discuss the potential use of patient-specific PSCs as an in vitro model, providing new insights into the pathophysiology of diabetes.

The specificity triad: notions of disease and therapeutic specificity in biomedical reasoning

Biomedicine is typically defined as the branch of medicine that is based on the principles of biology and biochemistry. A central tenet for biomedicine is the notion of disease and therapeutic specificity, i.e. the idea of tailored treatments for discrete disorders underpinned by specific pathologies. The present paper is concerned with how notions of disease and therapeutic specificity guide biomedical reasoning. To that end, the author proposes a model - the specificity triad - that draws on late philosopher and physician Ludwik Fleck's concept of "style of thought" to offer a frame for investigating the intricate process through which links between disorders, mechanisms, and therapeutics are established by biomedicine. Next by applying the specificity triad model to scrutinize research efforts in two discrete areas of medicine-psychiatry and regenerative medicine-this paper seeks to stimulate pertinent discussions in and about biomedicine. These include discussions on the ambiguous epistemic status of psychiatry within contemporary biomedicine, as well as the relationship between developmental biology - historically relatively disjointed from biomedical enterprise - and the burgeoning field of regenerative medicine.

The regulation of pre- and post-maturational plasticity of mammalian islet cell mass

Regeneration of mature cells that produce functional insulin represents a major focus and a challenge of current diabetes research aimed at restoring beta cell mass in patients with most forms of diabetes, as well as in ageing. The capacity to adapt to diverse physiological states during life and the consequent ability to cope with increased metabolic demands in the normal regulation of glucose homeostasis is a distinctive feature of the endocrine pancreas in mammals. Both beta and alpha cells, and presumably other islet cells, are dynamically regulated via nutrient, neural and/or hormonal activation of growth factor signalling and the post-transcriptional modification of a variety of genes or via the microbiome to continually maintain a balance between regeneration (e.g. proliferation, neogenesis) and apoptosis. Here we review key regulators that determine islet cell mass at different ages in mammals. Understanding the chronobiology and the dynamics and age-dependent processes that regulate the relationship between the different cell types in the overall maintenance of an optimally functional islet cell mass could provide important insights into planning therapeutic approaches to counter and/or prevent the development of diabetes.

Comparable generation of activin-induced definitive endoderm via additive Wnt or BMP signaling in absence of serum

There is considerable interest in differentiating human pluripotent stem cells (hPSCs) into definitive endoderm (DE) and pancreatic cells for in vitro disease modeling and cell replacement therapy. Numerous protocols use fetal bovine serum, which contains poorly defined factors to induce DE formation. Here, we compared Wnt and BMP in their ability to cooperate with Activin signaling to promote DE formation in a chemically defined medium. Varying concentrations of WNT3A, glycogen synthase kinase (GSK)-3 inhibitors CHIR99021 and 6-bromoindirubin-3′-oxime (BIO), and BMP4 could independently co-operate with Activin to effectively induce DE formation even in the absence of serum. Overall, CHIR99021 is favored due to its cost effectiveness. Surprisingly, WNT3A was ineffective in suppressing E-CADHERIN/CDH1 and pluripotency factor gene expression unlike GSK-3 inhibitors or BMP4. Our findings indicate that both Wnt and BMP effectively synergize with Activin signaling to generate DE from hPSCs, although WNT3A requires additional factors to suppress the pluripotency program inherent in hPSCs.

•

High dose of WNT3A cooperates with Activin to induce DE without serum

•

GSK-3 inhibitors, CHIR99021 and BIO, work with Activin to induce DE without serum

•

Wnt and BMP signaling can induce DE with comparable efficiencies without serum

•

WNT3A is not as effective as BMP4, CHIR99021, or BIO in suppressing pluripotency