Reprogramming of various cell types to a beta-like state by Pdx1, Ngn3 and MafA

Forward programming of hiPSCs towards beta-like cells using Ngn3, Pdx1, and MafA

Transplantation of stem cell-derived β-cells is a promising therapeutic advancement in the treatment of type 1 diabetes mellitus. A current limitation of this approach is the long differentiation timeline that generates a heterogeneous population of pancreatic endocrine cells. To address this limitation, an inducible lentiviral overexpression system of mature β-cell markers was introduced into human induced-pluripotent stem cells (hiPSCs). Following the selection of the successfully transduced hiPSCs, the cells were treated with doxycycline in the pancreatic progenitor induction medium to support their transition toward the pancreatic lineage. Cells cultured with doxycycline presented the markers of interest, NGN3, PDX1, and MAFA, after five days of culture, and glucose-stimulated insulin secretion assays demonstrated that the cells were glucose-responsive in a monolayer culture. When cultured as a spheroid, the markers of interest and insulin secretion in a static glucose-stimulated insulin secretion assay were maintained; however, insulin secretion upon consecutive glucose challenges was limited. Comparison to human fetal and adult donor tissues identified that although the hiPSC-derived spheroids present similar markers to adult insulin-producing cells, they are functionally representative of fetal development. Together, these results suggest that with optimization of the temporal expression of these markers, forward programming of hiPSCs towards insulin-producing cells could be a possible alternative for islet transplantation.

Degradation meets development: Implications in β-cell development and diabetes

Pancreatic development is orchestrated by timely synthesis and degradation of stage-specific transcription factors (TFs). The transition from one stage to another stage is dependent on the precise expression of the developmentally relevant TFs. Persistent expression of particular TF would impede the exit from the progenitor stage to the matured cell type. Intracellular protein degradation-mediated protein turnover contributes to a major extent to the turnover of these TFs and thereby dictates the development of different tissues. Since even subtle changes in the crucial cellular pathways would dramatically impact pancreatic β-cell performance, it is generally acknowledged that the biological activity of these pathways is tightly regulated by protein synthesis and degradation process. Intracellular protein degradation is executed majorly by the ubiquitin proteasome system (UPS) and Lysosomal degradation pathway. As more than 90% of the TFs are targeted to proteasomal degradation, this review aims to examine the crucial role of UPS in normal pancreatic β-cell development and how dysfunction of these pathways manifests in metabolic syndromes such as diabetes. Such understanding would facilitate designing a faithful approach to obtain a therapeutic quality of β-cells from stem cells.

Biochemical pancreatic β-cell lineage reprogramming: Various cell fate shifts

The incidence of pancreatic diseases has been continuously rising in recent years. Thus, research on pancreatic regeneration is becoming more popular. Chronic hyperglycemia is detrimental to pancreatic β-cells, leading to impairment of insulin secretion which is the main hallmark of pancreatic diseases. Obtaining plenty of functional pancreatic β-cells is the most crucial aspect when studying pancreatic biology and treating diabetes. According to the International Diabetes Federation, diabetes has become a global epidemic, with about 3 million people suffering from diabetes worldwide. Hyperglycemia can lead to many dangerous diseases, including amputation, blindness, neuropathy, stroke, and cardiovascular and kidney diseases. Insulin is widely used in the treatment of diabetes; however, innovative approaches are needed in the academic and preclinical stages. A new approach aims at synthesizing patient-specific functional pancreatic β-cells. The present article focuses on how cells from different tissues can be transformed into pancreatic β-cells.

Pancreatic beta cell regenerative potential of Zanthoxylum chalybeum Engl. Aqueous stem bark extract

ETHNOPHARMACOLOGICAL RELEVANCE

Zanthoxylum chalybeum Engl. is endemic to Africa and has been used traditionally to treat diabetes mellitus. Moreover, its pharmacological efficacy has been confirmed experimentally using in vitro and in vivo models of diabetes. However, the effects of Z. chalybeum extracts and its major constituent compounds on beta cell and islet regeneration are not clear. Further, the mechanisms associated with observed antidiabetic effects at the beta cell level are not fully elucidated.

AIM OF THE STUDY

We determined the beta cell regenerative efficacy of Z. chalybeum aqueous stem bark extract, identified the chemical compounds in Z. chalybeum aqueous stem bark extracts and explored their putative mechanisms of action.

MATERIALS AND METHODS

Phytochemical profiling of the Z. chalybeum extract was achieved using ultra high-performance liquid chromatography hyphenated to high-resolution mass spectrometry. Thereafter, molecular interactions of the compounds with beta cell regeneration targets were evaluated via molecular docking. In vitro, effects of the extract on cell viability, proliferation, apoptosis and oxidative stress were investigated in RIN-5F beta cells exposed to palmitate or streptozotocin. In vivo, pancreas tissue sections from streptozotocin-induced diabetic male Wistar rats treated with Z. chalybeum extract were stained for insulin, glucagon, pancreatic duodenal homeobox protein 1 (Pdx-1) and Ki-67.

RESULTS

Based on ligand target and molecular docking interactions diosmin was identified as a dual specificity tyrosine-phosphorylation-regulated kinase 1A (Dyrk1A) inhibitor. In vitro, Z. chalybeum augmented cell viability and cell proliferation while in palmitate-pre-treated cells, the extract significantly increased cell activity after 72 h. In vivo, although morphometric analysis showed decreased islet and beta cell size and density, observation of increased Pdx-1 and Ki-67 immunoreactivity in extract-treated islets suggests that Z. chalybeum extract has mild beta cell regenerative potential mediated by increased cell proliferation.

CONCLUSIONS

Overall, the mitogenic effects observed in vitro, were not robust enough to elicit sufficient recovery of functional beta cell mass in our in vivo model, in the context of a sustained diabetic milieu. However, the identification of diosmin as a potential Dyrk1A inhibitor merits further inquiry into the attendant molecular interactions.

Hepatic insulin synthesis increases in rat models of diabetes mellitus type 1 and 2 differently

Insulin-positive (+) cells (IPCs), detected in multiple organs, are of great interest as a probable alternative to ameliorate pancreatic beta-cells dysfunction and insulin deficiency in diabetes. Liver is a potential source of IPCs due to it common embryological origin with pancreas. We previously demonstrated the presence of IPCs in the liver of healthy and diabetic rats, but detailed description and analysis of the factors, which potentially can induced ectopic hepatic expression of insulin in type 1 (T1D) and type 2 diabetes (T2D), were not performed. In present study we evaluate mass of hepatic IPCs in the rat models of T1D and T2D and discuss factors, which may stimulate it generation: glycaemia, organ injury, involving of hepatic stem/progenitor cell compartment, expression of transcription factors and inflammation. Quantity of IPCs in the liver was up by 1.7-fold in rats with T1D and 10-fold in T2D compared to non-diabetic (ND) rats. We concluded that ectopic hepatic expression of insulin gene is activated by combined action of a number of factors, with inflammation playing a decision role.

Direct reprogramming of human fibroblasts into insulin-producing cells using transcription factors

Direct lineage reprogramming of one somatic cell into another without transitioning through a progenitor stage has emerged as a strategy to generate clinically relevant cell types. One cell type of interest is the pancreatic insulin-producing β cell whose loss and/or dysfunction leads to diabetes. To date it has been possible to create β-like cells from related endodermal cell types by forcing the expression of developmental transcription factors, but not from more distant cell lineages like fibroblasts. In light of the therapeutic benefits of choosing an accessible cell type as the cell of origin, in this study we set out to analyze the feasibility of transforming human skin fibroblasts into β-like cells. We describe how the timed-introduction of five developmental transcription factors (Neurog3, Pdx1, MafA, Pax4, and Nkx2-2) promotes conversion of fibroblasts toward a β-cell fate. Reprogrammed cells exhibit β-cell features including β-cell gene expression and glucose-responsive intracellular calcium mobilization. Moreover, reprogrammed cells display glucose-induced insulin secretion in vitro and in vivo. This work provides proof-of-concept of the capacity to make insulin-producing cells from human fibroblasts via transcription factor-mediated direct reprogramming.

Protocol for in vivo and ex vivo assessment of hyperglycemia and islet function in diabetic mice

Mouse hyperglycemia model and islet function assessment are essential in diabetes research. Here, we provide a protocol to evaluate glucose homeostasis and islet functions in diabetic mice and isolated islets. We describe steps for establishing type 1 and 2 diabetes, glucose tolerance test, insulin tolerance test, glucose stimulated insulin secretion (GSIS) assay, and histological analysis for islet number and insulin expression in vivo. We then detail islet isolation, islet GSIS, β-cell proliferation, apoptosis, and programming assays ex vivo. For complete details on the use and execution of this protocol, please refer to Zhang et al. (2022).1.

PDX1 is the cornerstone of pancreatic β-cell functions and identity

Diabetes has been a worldwide healthcare problem for many years. Current methods of treating diabetes are still largely directed at symptoms, aiming to control the manifestations of the pathology. This creates an overall need to find alternative measures that can impact on the causes of the disease, reverse diabetes, or make it more manageable. Understanding the role of key players in the pathogenesis of diabetes and the related β-cell functions is of great importance in combating diabetes. PDX1 is a master regulator in pancreas organogenesis, the maturation and identity preservation of β-cells, and of their role in normal insulin function. Mutations in the PDX1 gene are correlated with many pancreatic dysfunctions, including pancreatic agenesis (homozygous mutation) and MODY4 (heterozygous mutation), while in other types of diabetes, PDX1 expression is reduced. Therefore, alternative approaches to treat diabetes largely depend on knowledge of PDX1 regulation, its interaction with other transcription factors, and its role in obtaining β-cells through differentiation and transdifferentiation protocols. In this article, we review the basic functions of PDX1 and its regulation by genetic and epigenetic factors. Lastly, we summarize different variations of the differentiation protocols used to obtain β-cells from alternative cell sources, using PDX1 alone or in combination with various transcription factors and modified culture conditions. This review shows the unique position of PDX1 as a potential target in the genetic and cellular treatment of diabetes.

Type 1 diabetes and engineering enhanced islet transplantation

The development of new therapeutic approaches to treat type 1 diabetes mellitus (T1D) relies on the precise understanding and deciphering of insulin-secreting β-cell biology, as well as the mechanisms responsible for their autoimmune destruction. β-cell or islet transplantation is viewed as a potential long-term therapy for the millions of patients with diabetes. To advance the field of insulin-secreting cell transplantation, two main research areas are currently investigated by the scientific community: (1) the identification of the developmental pathways that drive the differentiation of stem cells into insulin-producing cells, providing an inexhaustible source of cells; and (2) transplantation strategies and engineered transplants to provide protection and enhance the functionality of transplanted cells. In this review, we discuss the biology of pancreatic β-cells, pathology of T1D and current state of β-cell differentiation. We give a comprehensive view and discuss the different possibilities to engineer enhanced insulin-secreting cell/islet transplantation from a translational perspective.

Pancreatic Transdifferentiation Using β-Cell Transcription Factors for Type 1 Diabetes Treatment

Type 1 diabetes is a chronic illness in which the native beta (β)-cell population responsible for insulin release has been the subject of autoimmune destruction. This condition requires patients to frequently measure their blood glucose concentration and administer multiple daily exogenous insulin injections accordingly. Current treatments fail to effectively treat the disease without significant side effects, and this has led to the exploration of different approaches for its treatment. Gene therapy and the use of viral vectors has been explored extensively and has been successful in treating a range of diseases. The use of viral vectors to deliver β-cell transcription factors has been researched in the context of type 1 diabetes to induce the pancreatic transdifferentiation of cells to replace the β-cell population destroyed in patients. Studies have used various combinations of pancreatic and β-cell transcription factors in order to induce pancreatic transdifferentiation and have achieved varying levels of success. This review will outline why pancreatic transcription factors have been utilised and how their application can allow the development of insulin-producing cells from non β-cells and potentially act as a cure for type 1 diabetes.

Pax4 synergistically acts with Pdx1, Ngn3 and MafA to induce HuMSCs to differentiate into functional pancreatic β-cells

It has been indicated that the combination of pancreatic and duodenal homeobox 1 (Pdx1), MAF bZIP transcription factor A (MafA) and neurogenin 3 (Ngn3) was able to reprogram various cell types towards pancreatic β-like cells (pβLCs). Paired box 4 (Pax4), a transcription factor, has a key role in regulating the maturation of pancreatic β-cells (pβCs). In the present study, it was investigated whether Pax4 is able to synergistically act with Pdx1, Ngn3 and MafA to induce human umbilical cord mesenchymal stem cells (HuMSCs) to differentiate into functional pβCs in vitro. HuMSCs were isolated, cultured and separately transfected with adenovirus (Ad) expressing enhanced green fluorescence protein, Pax4 (Ad-Pax4), Pdx1+MafA+Ngn3 (Ad-3F) or Ad-Pxa4 + Ad-3F. The expression of C-peptide, insulin and glucagon was detected by immunofluorescence. The transcription of a panel of genes was determined by reverse transcription-quantitative PCR, including glucagon (GCG), insulin (INS), NK6 homeobox 1 (NKX6-1), solute carrier family 2 member 2 (SLC2A2), glucokinase (GCK), proprotein convertase subtilisin/kexin type 1 (PCSK1), neuronal differentiation 1 (NEUROD1), ISL LIM homeobox 1 (ISL 1), Pax6 and PCSK type 2 (PCSK2). Insulin secretion stimulated by glucose was determined using ELISA. The results suggested that, compared with Ad-3F alone, cells co-transfected with Ad-Pax4 and Ad-3F expressed higher levels of INS and C-peptide, as well as genes expressed in pancreatic β precursor cells, and secreted more insulin in response to high glucose. Furthermore, the expression of GCG in cells transfected with Ad-3F was depressed by Ad-Pax4. The present study demonstrated that Pax4 was able to synergistically act with the transcription factors Pdx1, Ngn3 and MafA to convert HuMSCs to functional pβLCs. HuMSCs may be potential seed cells for generating functional pβLCs in the therapy of diabetes.

Liver to Pancreas Transdifferentiation

PURPOSE OF THE REVIEW

Here, we review recent findings in the field of generating insulin-producing cells by pancreatic transcription factor (pTF)-induced liver transdifferentiation (TD). TD is the direct conversion of functional cell types from one lineage to another without passing through an intermediate stage of pluripotency. We address potential reasons for the restricted efficiency of TD and suggest modalities to overcome these challenges, to bring TD closer to its clinical implementation in autologous cell replacement therapy for insulin-dependent diabetes.

RECENT FINDINGS

Liver to pancreas TD is restricted to cells that are a priori predisposed to undergo the developmental process. In vivo, the predisposition of liver cells is affected by liver zonation and hepatic regeneration. The TD propensity of liver cells is related to permissive epigenome which could be extended to TD-resistant cells by specific soluble factors. An obligatory role for active Wnt signaling in continuously maintaining a "permissive" epigenome is suggested. Moreover, the restoration of the pancreatic niche and vasculature promotes the maturation of TD cells along the β cell function. Future studies on liver to pancreas TD should include the maturation of TD cells by 3D culture, the restoration of vasculature and the pancreatic niche, and the extension of TD propensity to TD-resistant cells by epigenetic modifications. Liver to pancreas TD is expected to result in the generation of custom-made "self" surrogate β cells for curing diabetes.

Differentiation Potential of Mesenchymal Stem Cells into Pancreatic β-Cells

Stem cells having the capability to differentiate into other type of cells and renewing themselves, gained so much importance in recent years. Investigations in stem cells revealed that mesenchymal stem cells can successfully differentiate into other type of cells like adipocytes, hepatocytes, osteocytes, neurocytes and chondrocytes. In addition, these cells can also differentiate into insulin-producing beta cells. Insulin is a crucial hormone for glucose balance of the body. Insufficiency or unavailability of insulin is called diabetes. External insulin intake, as well as pancreas or islet transplantation, is the most basic treatment of diabetes. In vivo and in vitro studies demonstrate that stem cell therapy is also used in the cure of diabetes. Differentiation process of stem cells into beta cells releasing insulin is quite complicated. There are many different reports for the differentiation of stem cells in the literature. The success of differentiation of stem cells into beta cells depends on several factors like the source of stem cells, chemicals added into the differentiation medium and the duration of differentiation protocol. Distinct studies for the differentiation of stem cells into insulin-secreting cells are available in the literature. Moreover, thanks to the superior differentiation capacity of stem cells, they are being preferred in clinical studies. Stem cells were clinically used to heal diabetic ulcer, to increase c-peptide level and insulin secretion in both type 1 and type 2 diabetes. Mesenchymal stem cells having high differentiation potential to insulin-secreting cells are encouraging vehicles for both in vivo and in vitro studies together with clinical trials for diabetes mellitus.

Enhanced insulin production and reprogramming efficiency of mesenchymal stem cells derived from porcine pancreas using suitable induction medium

BACKGROUND

Genetic reprogramming is a powerful method for altering cell properties and inducing differentiation. However, even if the same gene is reprogrammed, the results vary among cells. Therefore, a better possible strategy involves treating cells with factors that further stimulate differentiation while using stem cells with the same tissue origin. This study aimed to increase induction efficiency and insulin production in reprogrammed cells using a combination of factors that promote cell differentiation.

METHODS

Porcine pancreatic cells were cultured to obtain mesenchymal stem cells expressing pancreatic cell-specific markers through sequential passages. The characteristics of these cells were identified, and the M3 gene (Pdx1, Ngn3, MafA) was reprogrammed to induce differentiation into insulin-producing cells. Additionally, the differentiation efficiency of insulin-producing cells was compared by treating reprogrammed cells with a differentiation-promoting factor.

RESULTS

Mesenchymal stem cells isolated from porcine pancreatic tissues expressed exocrine cell markers, including amylase and cytokeratin 18, and most cells continuously expressed the beta cell transcription factors Ngn3 and NeuroD. Reprogramming of the M3 gene resulted in differentiation into insulin-producing cells. Moreover, significantly increased insulin and glucagon expressions were observed in the suitable induction medium, and the characteristic beta cell transcription factors Pdx1, Ngn3, and MafA were expressed at levels as high as those in pancreatic islet cells.

CONCLUSIONS

Differentiation into insulin-producing cells represents an alternative therapy for insufficient pancreatic islet cells when treating diabetes. Therefore, cells with the characteristics of the target cell should be used to improve differentiation efficiency by creating an environment that promotes reprogramming and differentiation.

Cell-free culture conditioned medium elicits pancreatic β cell lineage-specific epigenetic reprogramming in mice

There are several obstacles to overcome prior to achieving cellular reprogramming of pancreatic β cells in vitro and in vivo. The present study demonstrated that the transfer of epigenetic phenotypes was achieved in the cell-free conditioned medium (CM) of pancreatic insulinoma MIN6 cell cultures. The comparison of a subpopulation of MIN6, m14 and m9 cells indicated that MIN6-m14 cells were more prone to cellular reprogramming. Epigenetic profiling revealed that the transcription factor pancreas/duodenum homeobox protein 1 (Pdx1) was differentially associated among the clones. The culture of differentiated adipocytes in the CM of MIN6-m14 cells resulted in the induction of insulin mRNA expression, and was accompanied by epigenetic events of Pdx1 binding. The epigenetic profiling indicated that Pdx1 is preferentially associated with a previously uncharacterized region of the endoplasmic reticulum (ER) disulfide oxidase, ER oxidoreductin 1 gene. Therefore, the results of the present study indicated that the CM of MIN6 cells was able to induce a pancreatic β cell-like phenotype in differentiated adipocytes. These data provide additional support for the utility of cell-free CM for cellular reprogramming.

Treatment with specific soluble factors promotes the functional maturation of transcription factor-mediated, pancreatic transdifferentiated cells

Pancreatic lineage-specific transcription factors (TFs) display instructive roles in converting adult cells to endocrine pancreatic cells through a process known as transdifferentiation. However, little is known about potential factors capable of accelerating transdifferentiation following transduction to achieve the functional maturation of transdifferentiated cells. In this study, we demonstrated, using adult liver-derived progenitor cells, that soluble factors utilized in pancreatic differentiation protocols of pluripotent stem cells promote functional maturation of TFs-mediated transdifferentiated cells. Treatment with an N2 supplement in combination with three soluble factors (glucagon-like peptide-1 [GLP-1] receptor agonist, notch inhibitor, and transforming growth factor-β [TGF-β] inhibitor) enhanced liver-to-pancreas transdifferentiation based on the following findings: i) the incidence of c-peptide-positive cells increased by approximately 1.2-fold after the aforementioned treatment; ii) the c-peptide expression level in the treated cells increased by approximately 12-fold as compared with the level in the untreated cells; iii) the treated cells secreted insulin in a glucose-dependent manner, whereas the untreated cells did not; and iv) transplantation of treated-transdifferentiated cells into streptozotocin-induced immunodeficient diabetic mice led to the amelioration of hyperglycemia. These results suggest that treatment with specific soluble factors promotes the functional maturation of transdifferentiated cells. Our findings could facilitate the development of new modalities for cell-replacement therapy for patients with diabetes.

Modulation of the endocrine transcriptional program by targeting histone modifiers of the H3K27me3 mark

Posttranscriptional modifications of histones constitute an epigenetic mechanism that is closely linked to both gene silencing and activation events. Trimethylation of Histone3 at lysine 27 (H3K27me3) is a repressive mark that associates with developmental gene regulation during differentiation programs. In the developing pancreas, expression of the transcription factor Neurogenin3 in multipotent progenitors initiates endocrine differentiation that culminates in the generation of all pancreatic islet cell lineages, including insulin-producing beta cells. Previously, we showed that Neurogenin3 promoted the removal of H3K27me3 marks at target gene promoters in vitro, suggesting a functional connection between this factor and regulators of this chromatin mark. In the present study, we aimed to specifically evaluate whether targeting the activity of these histone modifiers can be used to modulate pancreatic endocrine differentiation. Our data show that chemical inhibition of the H3K27me3 demethylases Jmjd3/Utx blunts Neurogenin3-dependent gene activation in vitro. Conversely, inhibition of the H3K27me3 methyltransferase Ezh2 enhances both the transactivation ability of Neurogenin3 in cultured cells and the formation of insulin-producing cells during directed differentiation from pluripotent cells. These results can help improve current protocols aimed at generating insulin-producing cells for beta cell replacement therapy in diabetes.

Improved insulin-secreting properties of pancreatic islet mesenchymal stem cells by constitutive expression of Pax4 and MafA

For long-term treatment of diabetes type 1, transplantation of insulin-producing beta cells may be a promising method, but the limited number of islets for transplantation requires the development of different approaches. In this study, we aimed to generate betalike insulin-producing cells. For this purpose, MafA, Pax4, and Ngn3 genes were transferred into pancreatic islet-derived mesenchymal stem cells, and the effect of their ectopic expressions on differentiation efficiency was examined. Stemness properties of pancreatic islet stem cells were characterized. The 3 genes were transfected by electroporation and expressed constitutively. The transfected cells were further stimulated to differentiate by using chemical induction. Pax4 expression had significant effects on differentiation into insulin-producing cells. Although it caused morphological alterations in cells, similar to epithelial cells, the insulin secretion levels remained lower than those of the cell line cotransfected with MafA and Pax4. Cotransfection of the 3 transcription factors did not further improve the beta-like cell generation. MafA and Pax4 ectopic expression resulted in improved differentiation efficiency into insulin-secreting cells. However, support of this differentiation process using additional chemical induction may sufice to overcome control by endogenous regulatory pathways.

PDX1, Neurogenin-3, and MAFA: critical transcription regulators for beta cell development and regeneration

Transcription factors regulate gene expression through binding to specific enhancer sequences. Pancreas/duodenum homeobox protein 1 (PDX1), Neurogenin-3 (NEUROG3), and V-maf musculoaponeurotic fibrosarcoma oncogene homolog A (MAFA) are transcription factors critical for beta cell development and maturation. NEUROG3 is expressed in endocrine progenitor cells and controls islet differentiation and regeneration. PDX1 is essential for the development of pancreatic exocrine and endocrine cells including beta cells. PDX1 also binds to the regulatory elements and increases insulin gene transcription. Likewise, MAFA binds to the enhancer/promoter region of the insulin gene and drives insulin expression in response to glucose. In addition to those natural roles in beta cell development and maturation, ectopic expression of PDX1, NEUROG3, and/or MAFA has been successfully used to reprogram various cell types into insulin-producing cells in vitro and in vivo, such as pancreatic exocrine cells, hepatocytes, and pluripotent stem cells. Here, we review biological properties of PDX1, NEUROG3, and MAFA, and their applications and limitations for beta cell regenerative approaches. The primary source literature for this review was acquired using a PubMed search for articles published between 1990 and 2017. Search terms include diabetes, insulin, trans-differentiation, stem cells, and regenerative medicine.

Reprogramming human gallbladder cells into insulin-producing β-like cells

The gallbladder and cystic duct (GBCs) are parts of the extrahepatic biliary tree and share a common developmental origin with the ventral pancreas. Here, we report on the very first genetic reprogramming of patient-derived human GBCs to β-like cells for potential autologous cell replacement therapy for type 1 diabetes. We developed a robust method for large-scale expansion of human GBCs ex vivo. GBCs were reprogrammed into insulin-producing pancreatic β-like cells by a combined adenoviral-mediated expression of hallmark pancreatic endocrine transcription factors PDX1, MAFA, NEUROG3, and PAX6 and differentiation culture in vitro. The reprogrammed GBCs (rGBCs) strongly induced the production of insulin and pancreatic endocrine genes and these responded to glucose stimulation in vitro. rGBCs also expressed an islet-specific surface marker, which was used to enrich for the most highly reprogrammed cells. More importantly, global mRNA and microRNA expression profiles and protein immunostaining indicated that rGBCs adopted an overall β-like state and these rGBCs engrafted in immunodeficient mice. Furthermore, comparative global expression analyses identified putative regulators of human biliary to β cell fate conversion. In summary, we have developed, for the first time, a reliable and robust genetic reprogramming and culture expansion of primary human GBCs—derived from multiple unrelated donors—into pancreatic β-like cells ex vivo, thus showing that human gallbladder is a potentially rich source of reprogrammable cells for autologous cell therapy in diabetes.

Establishing a Large-Animal Model for In Vivo Reprogramming of Bile Duct Cells into Insulin-Secreting Cells to Treat Diabetes

Type 1 diabetes manifests as autoimmune destruction of beta cells requiring metabolic management with an exogenous replacement of insulin, either by repeated injection of recombinant insulin or by transplantation of allogeneic islets from cadaveric donors. Both of these approaches have severe limitations. Repeated insulin injection requires intensive blood glucose monitoring, is expensive, and is associated with decreased quality-of-life measures. Islet transplantation, while highly effective, is severely limited by shortage of donor organs. Clinical translation of beta cells derived from pluripotent stem cells is also not yet a reality, and alternative approaches to solving the replacement of lost beta cell function are required. In vivo direct reprogramming offers an attractive approach to generating new endogenous insulin-secreting cells by permanently altering the phenotype of somatic cells after transient expression of transcription factors. Previously, we have successfully restored control of blood glucose in diabetic mice by reprogramming liver cells into glucose-sensitive insulin-secreting cells after the transient, simultaneous delivery of three transcription factors (Pdx1, Ngn3, and MafA) to the liver of diabetic mice, using an adenoviral vector (Ad-PNM). Establishing a clinically relevant, large-animal model is a critical next step in translating this approach beyond the proof-of-principle stage in rodents and allowing investigation of vector design, dose and delivery, host response to vector infusion, and establishment of suitable criteria for measuring safety and efficacy. In this feasibility study we infused Ad-PNM into the liver of three diabetic cynomolgus macaques via portal vein catheter. Vector presence and cargo gene and protein expression were detected in liver tissue after infusion with no adverse effects. Refinement of immune suppression significantly extended the period of exogenous PNM expression. This pilot study establishes the suitability of this large-animal model to examine the translation of this approach for treating diabetes.

Lineage Reprogramming: A Promising Road for Pancreatic β Cell Regeneration

Cell replacement therapy is a promising method to restore pancreatic β cell function and cure diabetes. Distantly related cells (fibroblasts, keratinocytes, and muscle cells) and developmentally related cells (hepatocytes, gastrointestinal, and pancreatic exocrine cells) have been successfully reprogrammed into β cells in vitro and in vivo. However, while some reprogrammed β cells bear similarities to bona fide β cells, others do not develop into fully functional β cells. Here we review various strategies currently used for β cell reprogramming, including ectopic expression of specific transcription factors associated with islet development, repression of maintenance factors of host cells, regulation of epigenetic modifications, and microenvironmental changes. Development of simple and efficient reprogramming methods is a key priority for developing fully functional β cells suitable for cell replacement therapy.

Reprogramming of liver cells into insulin-producing cells

Tissue replacement is a promising direction for the treatment of diabetes, which will become widely available only when islets or insulin-producing cells that will not be rejected by the diabetic recipients are available in unlimited amounts. The present review addresses the research in the field of generating functional insulin-producing cells by transdifferentiation of adult liver cells both in vitro and in vivo. It presents recent knowledge of the mechanisms which underlie the process and assesses the challenges which should be addressed for its efficient implementation as a cell based replacement therapy for diabetics.

Proper activation of MafA is required for optimal differentiation and maturation of pancreatic β-cells

A key therapeutic approach for the treatment of Type 1 diabetes (T1D) is transplantation of functional islet β-cells. Despite recent advances in generating stem cell-derived glucose-responsive insulin(+) cells, their further maturation to fully functional adult β-cells still remains a daunting task. Conquering this hurdle will require a better understanding of the mechanisms driving maturation of embryonic insulin(+) cells into adult β-cells, and the implementation of that knowledge to improve current differentiation protocols. Here, we will review our current understanding of β-cell maturation, and discuss the contribution of key β-cell transcription factor MafA, to this process. The fundamental importance of MafA in regulating adult β-cell maturation and function indicates that enhancing MafA expression may improve the generation of definitive β-cells for transplantation. Additionally, we suggest that the temporal control of MafA induction at a specific stage of β-cell differentiation will be the next critical challenge for achieving optimum maturation of β-cells.

MLL3 and MLL4 Methyltransferases Bind to the MAFA and MAFB Transcription Factors to Regulate Islet β-Cell Function

Insulin produced by islet β-cells plays a critical role in glucose homeostasis, with type 1 and type 2 diabetes both resulting from inactivation and/or loss of this cell population. Islet-enriched transcription factors regulate β-cell formation and function, yet little is known about the molecules recruited to mediate control. An unbiased in-cell biochemical and mass spectrometry strategy was used to isolate MafA transcription factor-binding proteins. Among the many coregulators identified were all of the subunits of the mixed-lineage leukemia 3 (Mll3) and 4 (Mll4) complexes, with histone 3 lysine 4 methyltransferases strongly associated with gene activation. MafA was bound to the ∼1.5 MDa Mll3 and Mll4 complexes in size-fractionated β-cell extracts. Likewise, closely related human MAFB, which is important to β-cell formation and coproduced with MAFA in adult human islet β-cells, bound MLL3 and MLL4 complexes. Knockdown of NCOA6, a core subunit of these methyltransferases, reduced expression of a subset of MAFA and MAFB target genes in mouse and human β-cell lines. In contrast, a broader effect on MafA/MafB gene activation was observed in mice lacking NCoA6 in islet β-cells. We propose that MLL3 and MLL4 are broadly required for controlling MAFA and MAFB transactivation during development and postnatally.

Minireview: Directed Differentiation and Encapsulation of Islet β-Cells-Recent Advances and Future Considerations

Diabetes mellitus has rapidly become a 21st century epidemic with the promise to create vast economic and health burdens, if left unchecked. The 2 major forms of diabetes arise from unique causes, with outcomes being an absolute (type 1) or relative (type 2) loss of functional pancreatic islet β-cell mass. Currently, patients rely on exogenous insulin and/or other pharmacologies that restore glucose homeostasis. Although these therapies have prolonged countless lives over the decades, the striking increases in both type 1 and type 2 diabetic diagnoses worldwide suggest a need for improved treatments. To this end, islet biologists are developing cell-based therapies by which a patient's lost insulin-producing β-cell mass is replenished. Pancreatic or islet transplantation from cadaveric donors into diabetic patients has been successful, yet the functional islet demand far surpasses supply. Thus, the field has been striving toward transplantation of renewable in vitro-derived β-cells that can restore euglycemia. Challenges have been numerous, but progress over the past decade has generated much excitement. In this review we will summarize recent findings that have placed us closer than ever to β-cell replacement therapies. With the promise of cell-based diabetes therapies on the horizon, we will also provide an overview of cellular encapsulation technologies that will deliver critical protection of newly implanted cells.

The FOXP1, FOXP2 and FOXP4 transcription factors are required for islet alpha cell proliferation and function in mice

AIMS/HYPOTHESIS

Several forkhead box (FOX) transcription factor family members have important roles in controlling pancreatic cell fates and maintaining beta cell mass and function, including FOXA1, FOXA2 and FOXM1. In this study we have examined the importance of FOXP1, FOXP2 and FOXP4 of the FOXP subfamily in islet cell development and function.

METHODS

Mice harbouring floxed alleles for Foxp1, Foxp2 and Foxp4 were crossed with pan-endocrine Pax6-Cre transgenic mice to generate single and compound Foxp mutant mice. Mice were monitored for changes in glucose tolerance by IPGTT, serum insulin and glucagon levels by radioimmunoassay, and endocrine cell development and proliferation by immunohistochemistry. Gene expression and glucose-stimulated hormone secretion experiments were performed with isolated islets.

RESULTS

Only the triple-compound Foxp1/2/4 conditional knockout (cKO) mutant had an overt islet phenotype, manifested physiologically by hypoglycaemia and hypoglucagonaemia. This resulted from the reduction in glucagon-secreting alpha cell mass and function. The proliferation of alpha cells was profoundly reduced in Foxp1/2/4 cKO islets through the effects on mediators of replication (i.e. decreased Ccna2, Ccnb1 and Ccnd2 activators, and increased Cdkn1a inhibitor). Adult islet Foxp1/2/4 cKO beta cells secrete insulin normally while the remaining alpha cells have impaired glucagon secretion.

CONCLUSIONS/INTERPRETATION

Collectively, these findings reveal an important role for the FOXP1, 2, and 4 proteins in governing postnatal alpha cell expansion and function.

Epigenetic-mediated reprogramming of pancreatic endocrine cells

SIGNIFICANCE

Type 1 diabetes (T1D) results from cell-mediated autoimmune destruction of insulin-secreting pancreatic beta cells (β-cells). In the context of T1D, the scarcity of organ donors has driven research to alternate sources of functionally competent, insulin-secreting β-cells as substitute for donor islets to meet the clinical need for transplantation therapy.

RECENT ADVANCES

Experimental evidence of an inherent plasticity of pancreatic cells has fuelled interest in in vivo regeneration of β-cells. Transcriptional modulation and direct reprogramming of noninsulin secreting pancreatic α-cells to functionally mimic insulin-secreting β-cells is one of the promising avenues to the treatment of diabetes. Recent studies now show that adult progenitor and glucagon(+) α-cells can be converted into β-like cells in vivo, as a result of specific activation of the Pax4 gene in α-cells and curing diabetes in preclinical models.

CRITICAL ISSUES

The challenge now is to understand the precise developmental transitions mediated by endocrine transcription factors and co-regulatory determinants responsible for pancreatic function and repair.

FUTURE DIRECTIONS

Epigenetic-mediated regulation of transcription factor binding in pancreatic α-cells by specific drugs to direct reprogramming into functional insulin producing cells could be of potential innovative therapy for the treatment of T1D.

De novo formation of insulin-producing "neo-β cell islets" from intestinal crypts

The ability to interconvert terminally differentiated cells could serve as a powerful tool for cell-based treatment of degenerative diseases, including diabetes mellitus. To determine which, if any, adult tissues are competent to activate an islet β cell program, we performed an in vivo screen by expressing three β cell “reprogramming factors” in a wide spectrum of tissues. We report that transient intestinal expression of these factors—Pdx1, MafA, and Ngn3 (PMN)—promotes rapid conversion of intestinal crypt cells into endocrine cells, which coalesce into “neoislets” below the crypt base. Neoislet cells express insulin and show ultrastructural features of β cells. Importantly, intestinal neoislets are glucose-responsive and able to ameliorate hyperglycemia in diabetic mice. Moreover, PMN expression in human intestinal “organoids” stimulates the conversion of intestinal epithelial cells into β-like cells. Our results thus demonstrate that the intestine is an accessible and abundant source of functional insulin-producing cells.