In vivo reprogramming of pancreatic acinar cells to three islet endocrine subtypes

Development, regeneration, and physiological expansion of functional β-cells: Cellular sources and regulators

Pancreatic regeneration is a complex process observed in both normal and pathological conditions. The aim of this review is to provide a comprehensive understanding of the emergence of a functionally active population of insulin-secreting β-cells in the adult pancreas. The renewal of β-cells is governed by a multifaceted interaction between cellular sources of genetic and epigenetic factors. Understanding the development and heterogeneity of β-cell populations is crucial for functional β-cell regeneration. The functional mass of pancreatic β-cells increases in situations such as pregnancy and obesity. However, the specific markers of mature β-cell populations and postnatal pancreatic progenitors capable of increasing self-reproduction in these conditions remain to be elucidated. The capacity to regenerate the β-cell population through various pathways, including the proliferation of pre-existing β-cells, β-cell neogenesis, differentiation of β-cells from a population of progenitor cells, and transdifferentiation of non-β-cells into β-cells, reveals crucial molecular mechanisms for identifying cellular sources and inducers of functional cell renewal. This provides an opportunity to identify specific cellular sources and mechanisms of regeneration, which could have clinical applications in treating various pathologies, including in vitro cell-based technologies, and deepen our understanding of regeneration in different physiological conditions.

Pancreatic islet transplantation: current advances and challenges

Diabetes is a prevalent chronic disease that traditionally requires severe reliance on medication for treatment. Oral medication and exogenous insulin can only temporarily maintain blood glucose levels and do not cure the disease. Most patients need life-long injections of exogenous insulin. In recent years, advances in islet transplantation have significantly advanced the treatment of diabetes, allowing patients to discontinue exogenous insulin and avoid complications.Long-term follow-up results from recent reports on islet transplantation suggest that they provide significant therapeutic benefit although patients still require immunotherapy, suggesting the importance of future transplantation strategies. Although organ shortage remains the primary obstacle for the development of islet transplantation, new sources of islet cells, such as stem cells and porcine islet cells, have been proposed, and are gradually being incorporated into clinical research. Further research on new transplantation sites, such as the subcutaneous space and mesenteric fat, may eventually replace the traditional portal vein intra-islet cell infusion. Additionally, the immunological rejection reaction in islet transplantation will be resolved through the combined application of immunosuppressant agents, islet encapsulation technology, and the most promising mesenchymal stem cells/regulatory T cell and islet cell combined transplantation cell therapy. This review summarizes the progress achieved in islet transplantation, and discusses the research progress and potential solutions to the challenges faced.

Acinar to β-like cell conversion through inhibition of focal adhesion kinase

Insufficient functional β-cell mass causes diabetes; however, an effective cell replacement therapy for curing diabetes is currently not available. Reprogramming of acinar cells toward functional insulin-producing cells would offer an abundant and autologous source of insulin-producing cells. Our lineage tracing studies along with transcriptomic characterization demonstrate that treatment of adult mice with a small molecule that specifically inhibits kinase activity of focal adhesion kinase results in trans-differentiation of a subset of peri-islet acinar cells into insulin producing β-like cells. The acinar-derived insulin-producing cells infiltrate the pre-existing endocrine islets, partially restore β-cell mass, and significantly improve glucose homeostasis in diabetic mice. These findings provide evidence that inhibition of the kinase activity of focal adhesion kinase can convert acinar cells into insulin-producing cells and could offer a promising strategy for treating diabetes.

From islet transplantation to beta-cell regeneration: an update on beta-cell-based therapeutic approaches in type 1 diabetes

INTRODUCTION

Type 1 diabetes (T1D) mellitus is an autoimmune disease in which immune cells, predominantly effector T cells, destroy insulin-secreting beta-cells. Beta-cell destruction led to various consequences ranging from retinopathy and nephropathy to neuropathy. Different strategies have been developed to achieve normoglycemia, including exogenous glucose compensation, whole pancreas transplantation, islet transplantation, and beta-cell replacement.

AREAS COVERED

The last two decades of experience have shown that indigenous glucose compensation through beta-cell regeneration and protection is a peerless method for T1D therapy. Tremendous studies have tried to find an unlimited source for beta-cell regeneration, on the one hand, and beta-cell protection against immune attack, on the other hand. Recent advances in stem cell technology, gene editing methods, and immune modulation approaches provide a unique opportunity for both beta-cell regeneration and protection.

EXPERT OPINION

Pluripotent stem cell differentiation into the beta-cell is considered an unlimited source for beta-cell regeneration. Devising engineered pancreas-specific regulatory T cells using Chimeric Antigen Receptor (CAR) technology potentiates an effective immune tolerance induction for beta-cell protection. Beta-cell regeneration using pluripotent stem cells and beta-cell protection using pancreas-specific engineered regulatory T cells promises to develop a curative protocol in T1D.

Therapeutic approaches for Type 1 Diabetes: Promising cell-based approaches to achieve ultimate success

Type 1 Diabetes mellitus (T1DM) is a chronic metabolic disorder characterized by pancreatic β-cells destruction. Despite substantial advances in T1DM treatment, lifelong exogenous insulin administration is the mainstay of treatments, and constant control of glucose levels is still a challenge. Endogenous insulin production by replacing insulin-producing cells is an alternative, but the lack of suitable donors is accounted as one of the main obstacles to its widespread application. The research and trials overview demonstrates that endogenous production of insulin has started to go beyond the deceased-derived to stem cells-derived insulin-producing cells. Several protocols have been developed over the past couple of years for generating insulin-producing cells (IPCs) from various stem cell types and reprogramming fully differentiated cells. A straightforward and quick method for achieving this goal is to investigate and apply the β-cell specific transcription factors as a direct strategy for IPCs generation. In this review, we emphasize the significance of transcription factors in IPCs development from different non-beta cell sources, and pertinent research underlies the marked progress in the methods for generating insulin-producing cells and application for Type 1 Diabetes treatment.

Hypoxia within subcutaneously implanted macroencapsulation devices limits the viability and functionality of densely loaded islets

Introduction

Subcutaneous macroencapsulation devices circumvent disadvantages of intraportal islet therapy. However, a curative dose of islets within reasonably sized devices requires dense cell packing. We measured internal PO2 of implanted devices, mathematically modeled oxygen availability within devices and tested the predictions with implanted devices containing densely packed human islets.

Methods

Partial pressure of oxygen (PO2) within implanted empty devices was measured by noninvasive 19F-MRS. A mathematical model was constructed, predicting internal PO2, viability and functionality of densely packed islets as a function of external PO2. Finally, viability was measured by oxygen consumption rate (OCR) in day 7 explants loaded at various islet densities.

Results

In empty devices, PO2 was 12 mmHg or lower, despite successful external vascularization. Devices loaded with human islets implanted for 7 days, then explanted and assessed by OCR confirmed trends proffered by the model but viability was substantially lower than predicted. Co-localization of insulin and caspase-3 immunostaining suggested that apoptosis contributed to loss of beta cells.

Discussion

Measured PO2 within empty devices declined during the first few days post-transplant then modestly increased with neovascularization around the device. Viability of islets is inversely related to islet density within devices.

Effect of lawsone-preconditioned mesenchymal stem cells on the regeneration of pancreatic β cells in Type 1 diabetic rats

Diabetes is one of the major health issues globally. Type 1 diabetes mellitus develops due to the destruction of pancreatic β cells. Mesenchymal stem cells (MSCs) having remarkable self-renewal and differentiation potential, can regenerate β cells. MSCs preconditioned with bioactive small molecules possess enhanced biological features and therapeutic potential under in vivo environment. Interestingly, compounds of naphthoquinone class possess antidiabetic and anti-inflammatory properties, and can be explored as potential candidates for preconditioning MSCs. This study analyzed the effect of lawsone-preconditioned human umbilical cord MSCs (hUMSCs) on the regeneration of β cells in the streptozotocin (STZ)-induced Type 1 diabetes (T1D) rats. hUMSCs were isolated and characterized for the presence of surface markers. MSCs were preconditioned with optimized concentration of lawsone. T1D rat model was established by injecting 50 mg/kg of STZ intraperitoneally. Untreated and lawsone-preconditioned hUMSCs were transplanted into the diabetic rats via tail vein. Fasting blood sugar and body weight were monitored regularly for 4 weeks. Pancreas was harvested and β cell regeneration was evaluated by hematoxylin and eosin staining, and gene expression analysis. Immunohistochemistry was also done to assess the insulin expression. Lawsone-preconditioned hUMSCs showed better anti-hyperglycemic effect in comparison with untreated hUMSCs. Histological analysis presented the regeneration of islets of Langerhans with upregulated expression of βcell genes and reduced expression of inflammatory markers. Immunohistochemistry revealed strong insulin expression in the preconditioned hUMSCs compared with the untreated hUMSCs. It is concluded from the present study that lawsone-preconditioned hMSCs were able to exhibit pronounced anti-hyperglycemic effect in vivo compared with hUMSCs alone.

Decoding pancreatic endocrine cell differentiation and β cell regeneration in zebrafish

In contrast to mice, zebrafish have an exceptional yet elusive ability to replenish lost β cells in adulthood. Understanding this framework would provide mechanistic insights for β cell regeneration, which may be extrapolated to humans. Here, we characterize a krt4-expressing ductal cell type, which is distinct from the putative Notch-responsive cells, showing neogenic competence and giving rise to the majority of endocrine cells during postembryonic development. Furthermore, we demonstrate a marked ductal remodeling process featuring a Notch-responsive to krt4+ luminal duct transformation during late development, indicating several origins of krt4+ ductal cells displaying similar transcriptional patterns. Single-cell transcriptomics upon a series of time points during β cell regeneration unveil a previously unrecognized dlb+ transitional endocrine precursor cell, distinct regulons, and a differentiation trajectory involving cellular shuffling through differentiation and dedifferentiation dynamics. These results establish a model of zebrafish pancreatic endocrinogenesis and highlight key values of zebrafish for translational studies of β cell regeneration.

Acinar cells and the development of pancreatic fibrosis

Pancreatic fibrosis is caused by excessive deposition of extracellular matrixes of collagen and fibronectin in the pancreatic tissue as a result of repeated injury often seen in patients with chronic pancreatic diseases. The most common causative conditions include inborn errors of metabolism, chemical toxicity and autoimmune disorders. Its pathophysiology is highly complex, including acinar cell injury, acinar stress response, duct dysfunction, pancreatic stellate cell activation, and persistent inflammatory response. However, the specific mechanism remains to be fully clarified. Although the current therapeutic strategies targeting pancreatic stellate cells show good efficacy in cell culture and animal models, they are not satisfactory in the clinic. Without effective intervention, pancreatic fibrosis can promote the transformation from pancreatitis to pancreatic cancer, one of the most lethal malignancies. In the normal pancreas, the acinar component accounts for 82% of the exocrine tissue. Abnormal acinar cells may activate pancreatic stellate cells directly as cellular source of fibrosis or indirectly via releasing various substances and initiate pancreatic fibrosis. A comprehensive understanding of the role of acinar cells in pancreatic fibrosis is critical for designing effective intervention strategies. In this review, we focus on the role of and mechanisms underlying pancreatic acinar injury in pancreatic fibrosis and their potential clinical significance.

Charting a high-resolution roadmap for regeneration of pancreatic β cells by in vivo transdifferentiation from adult acinar cells

Adult mammals have limited capacity to regenerate functional cells. Promisingly, in vivo transdifferentiation heralds the possibility of regeneration by lineage reprogramming from other fully differentiated cells. However, the process of regeneration by in vivo transdifferentiation in mammals is poorly understood. Using pancreatic β cell regeneration as a paradigm, we performed a single-cell transcriptomic study of in vivo transdifferentiation from adult mouse acinar cells to induced β cells. Using unsupervised clustering analysis and lineage trajectory construction, we uncovered that the cell fate remodeling trajectory was linear at the initial stage and the reprogrammed cells either evolved to induced β cells or toward a "dead-end" state after day 4.Moreover, functional analyses identified both p53 and Dnmt3a that acted as reprogramming barriers during the process of in vivo transdifferentiation. Collectively, we decipher a high-resolution roadmap of regeneration by in vivo transdifferentiation and provide a detailed molecular blueprint to facilitate mammalian regeneration.

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.

Direct Reprogramming of Different Cell Lineages into Pancreatic β-Like Cells

One major goal of regenerative medicine is the production of pancreatic endocrine islets to treat insulin-dependent diabetic patients. Among the different methods developed to achieve this goal, a particularly promising approach is direct lineage reprogramming, in which non-β-cells are directly converted to glucose-responsive, insulin-secreting β-like cells. Efforts by different research groups have led to critical insights in the inducing factors necessary and types of somatic tissues suitable for direct conversion to β-like cells. Nevertheless, there is limited understanding of the molecular mechanisms underlying direct cell fate conversion. Significant challenges also remain in translating discoveries into therapeutics that will eventually benefit diabetic patients. This review aims to cover the advances made in the direct reprogramming of somatic cells into β-like cells and discuss the remaining challenges.

Recombinant Reg3α Prevents Islet β-Cell Apoptosis and Promotes β-Cell Regeneration

Progressive loss and dysfunction of islet β-cells has not yet been solved in the treatment of diabetes. Regenerating protein (Reg) has been identified as a trophic factor which is demonstrated to be associated with pancreatic tissue regeneration. We previously produced recombinant Reg3α protein (rReg3α) and proved that it protects against acute pancreatitis in mice. Whether rReg3α protects islet β-cells in diabetes has been elusive. In the present study, rReg3α stimulated MIN6 cell proliferation and resisted STZ-caused cell death. The protective effect of rReg3α was also found in mouse primary islets. In BALB/c mice, rReg3α administration largely alleviated STZ-induced diabetes by the preservation of β-cell mass. The protective mechanism could be attributed to Akt/Bcl-2/-xL activation and GRP78 upregulation. Scattered insulin-expressing cells and clusters with small size, low insulin density, and exocrine distribution were observed and considered to be neogenic. In isolated acinar cells with wheat germ agglutinin (WGA) labeling, rReg3α treatment generated insulin-producing cells through Stat3/Ngn3 signaling, but these cells were not fully functional in response to glucose stimulation. Our results demonstrated that rReg3α resists STZ-induced β-cell death and promotes β-cell regeneration. rReg3α could serve as a potential drug for β-cell maintenance in anti-diabetic treatment.

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.

Single-cell transcriptome and accessible chromatin dynamics during endocrine pancreas development

Delineating gene regulatory networks that orchestrate cell-type specification is a continuing challenge for developmental biologists. Single-cell analyses offer opportunities to address these challenges and accelerate discovery of rare cell lineage relationships and mechanisms underlying hierarchical lineage decisions. Here, we describe the molecular analysis of mouse pancreatic endocrine cell differentiation using single-cell transcriptomics, chromatin accessibility assays coupled to genetic labeling, and cytometry-based cell purification. We uncover transcription factor networks that delineate β-, α-, and δ-cell lineages. Through genomic footprint analysis, we identify transcription factor-regulatory DNA interactions governing pancreatic cell development at unprecedented resolution. Our analysis suggests that the transcription factor Neurog3 may act as a pioneer transcription factor to specify the pancreatic endocrine lineage. These findings could improve protocols to generate replacement endocrine cells from renewable sources, like stem cells, for diabetes therapy.

Clinical significance of pancreatic ductal metaplasia

Pancreatic ductal metaplasia (PDM) is the stepwise replacement of differentiated somatic cells with ductal or ductal-like cells in the pancreas. PDM is usually triggered by cellular and environmental insults. PDM development may involve all cell lineages of the pancreas, and acinar cells with the highest plasticity are the major source of PDM. Pancreatic progenitor cells are also involved as cells of origin or transitional intermediates. PDM is heterogeneous at the histological, cellular, and molecular levels and only certain subsets of PDM develop further into pancreatic intraepithelial neoplasia (PanIN) and then pancreatic ductal adenocarcinoma (PDAC). The formation and evolution of PDM is regulated at the cellular and molecular levels through a complex network of signaling pathways. The key molecular mechanisms that drive PDM formation and its progression into PanIN/PDAC remain unclear, but represent key targets for reversing or inhibiting PDM. Alternatively, PDM could be a source of pancreas regeneration, including both exocrine and endocrine components. Cellular aging and apoptosis are obstacles to PDM-to-PanIN progression or pancreas regeneration. Functional identification of the cellular and molecular events driving senescence and apoptosis in PDM and its progression would help not only to restrict the development of PDM into PanIN/PDAC, but may also facilitate pancreatic regeneration. This review systematically assesses recent advances in the understanding of PDM physiology and pathology, with a focus on its implications for enhancing regeneration and prevention of cancer. © 2022 The Pathological Society of Great Britain and Ireland.

Valproic Acid Initiates Transdifferentiation of the Human Ductal Adenocarcinoma Cell-line Panc-1 Into α-Like Cells

Non-mesenchymal pancreatic cells are a potential source for cell replacement. Their transdifferentiation can be achieved by triggering epigenetic remodeling through e. g. post-translational modification of histones. Valproic acid, a branched-chain saturated fatty acid with histone deacetylase inhibitor activity, was linked to the expression of key transcription factors of pancreatic lineage in epithelial cells and insulin transcription. However, the potential of valproic acid to cause cellular reprogramming is not fully understood. To shed further light on it we employed next-generation RNA sequencing, real-time PCR, and protein analyses by ELISA and western blot, to assess the impact of valproic acid on transcriptome and function of Panc-1-cells. Our results indicate that valproic acid has a significant impact on the cell cycle, cell adhesion, histone H3 acetylation, and metabolic pathways as well as the initiation of epithelial-mesenchymal transition through acetylation of histone H3 resulting in α-cell-like characteristics. We conclude that human epithelial pancreatic cells can be transdifferentiated into cells with endocrine properties through epigenetic regulation by valproic acid favoring an α-cell-like phenotype.

Molecular signaling in pancreatic ductal metaplasia: emerging biomarkers for detection and intervention of early pancreatic cancer

Pancreatic ductal metaplasia (PDM) is the transformation of potentially various types of cells in the pancreas into ductal or ductal-like cells, which eventually replace the existing differentiated somatic cell type(s). PDM is usually triggered by and manifests its ability to adapt to environmental stimuli and genetic insults. The development of PDM to atypical hyperplasia or dysplasia is an important risk factor for pancreatic intraepithelial neoplasia (PanIN) and pancreatic ductal adenocarcinoma (PDA). Recent studies using genetically engineered mouse models, cell lineage tracing, single-cell sequencing and others have unraveled novel cellular and molecular insights in PDM formation and evolution. Those novel findings help better understand the cellular origins and functional significance of PDM and its regulation at cellular and molecular levels. Given that PDM represents the earliest pathological changes in PDA initiation and development, translational studies are beginning to define PDM-associated cell and molecular biomarkers that can be used to screen and detect early PDA and to enable its effective intervention, thereby truly and significantly reducing the dreadful mortality rate of PDA. This review will describe recent advances in the understanding of PDM biology with a focus on its underlying cellular and molecular mechanisms, and in biomarker discovery with clinical implications for the management of pancreatic regeneration and tumorigenesis.

Differentiation of PANC-1 ductal cells to β-like cells via cellular GABA modulation by Magainin and CPF-7 peptides

Some of the antimicrobial peptides induce insulin release and improve glucose tolerance while their effects on pancreatic cell differentiation have remained unresolved. In this report, we evaluated the effects of two of these peptides, Magainin-II and CPF-7, and also GABA, on PANC-1 ductal cells' differentiation. Based on immunofluorescence and qRT-PCR analyses the expression levels of some of the Epithelial to Mesenchymal transition (EMT)-related factors such as Snai1 and Ngn3, as two biomarkers of alpha and beta cells, were increased. Our findings also revealed a drastic increase in Arx, Pax4, Dnmt-1 and Glucagon expressions associated with dedifferentiation of PANC-1 cells into pancreatic endocrine progenitor cells. Futhermore, Magainin-II and CPF-7 exerted their roles partly via influencing the GABA cellular content. These data would undoubtedly provide a suitable ground for further investigation to guide these cells toward transplantable insulin producing beta cells.

Alpha-to-beta cell trans-differentiation for treatment of diabetes

Diabetes mellitus is a significant cause of morbidity and mortality in the United States and worldwide. According to the CDC, in 2017, ∼34.2 million of the American population had diabetes. Also, in 2017, diabetes was the seventh leading cause of death and has become the number one biomedical financial burden in the United States. Insulin replacement therapy and medications that increase insulin secretion and improve insulin sensitivity are the main therapies used to treat diabetes. Unfortunately, there is currently no radical cure for the different types of diabetes. Loss of β cell mass is the end result that leads to both type 1 and type 2 diabetes. In the past decade, there has been an increased effort to develop therapeutic strategies to replace the lost β cell mass and restore insulin secretion. α cells have recently become an attractive target for replacing the lost β cell mass, which could eventually be a potential strategy to cure diabetes. This review highlights the advantages of using α cells as a source for generating new β cells, the various investigative approaches to convert α cells into insulin-producing cells, and the future prospects and problems of this promising diabetes therapeutic strategy.

Stem/progenitor cells in normal physiology and disease of the pancreas

Though embryonic pancreas progenitors are well characterised, the existence of stem/progenitor cells in the postnatal mammalian pancreas has been long debated, mainly due to contradicting results on regeneration after injury or disease in mice. Despite these controversies, sequencing advancements combined with lineage tracing and organoid technologies indicate that homeostatic and trigger-induced regenerative responses in mice could occur. The presence of putative progenitor cells in the adult pancreas has been proposed during homeostasis and upon different stress challenges such as inflammation, tissue damage and oncogenic stress. More recently, single cell transcriptomics has revealed a remarkable heterogeneity in all pancreas cell types, with some cells showing the signature of potential progenitors. In this review we provide an overview on embryonic and putative adult pancreas progenitors in homeostasis and disease, with special emphasis on in vitro culture systems and scRNA-seq technology as tools to address the progenitor nature of different pancreatic cells.

Cell Fate Reprogramming in the Era of Cancer Immunotherapy

Advances in understanding how cancer cells interact with the immune system allowed the development of immunotherapeutic strategies, harnessing patients' immune system to fight cancer. Dendritic cell-based vaccines are being explored to reactivate anti-tumor adaptive immunity. Immune checkpoint inhibitors and chimeric antigen receptor T-cells (CAR T) were however the main approaches that catapulted the therapeutic success of immunotherapy. Despite their success across a broad range of human cancers, many challenges remain for basic understanding and clinical progress as only a minority of patients benefit from immunotherapy. In addition, cellular immunotherapies face important limitations imposed by the availability and quality of immune cells isolated from donors. Cell fate reprogramming is offering interesting alternatives to meet these challenges. Induced pluripotent stem cell (iPSC) technology not only enables studying immune cell specification but also serves as a platform for the differentiation of a myriad of clinically useful immune cells including T-cells, NK cells, or monocytes at scale. Moreover, the utilization of iPSCs allows introduction of genetic modifications and generation of T/NK cells with enhanced anti-tumor properties. Immune cells, such as macrophages and dendritic cells, can also be generated by direct cellular reprogramming employing lineage-specific master regulators bypassing the pluripotent stage. Thus, the cellular reprogramming toolbox is now providing the means to address the potential of patient-tailored immune cell types for cancer immunotherapy. In parallel, development of viral vectors for gene delivery has opened the door for in vivo reprogramming in regenerative medicine, an elegant strategy circumventing the current limitations of in vitro cell manipulation. An analogous paradigm has been recently developed in cancer immunotherapy by the generation of CAR T-cells in vivo. These new ideas on endogenous reprogramming, cross-fertilized from the fields of regenerative medicine and gene therapy, are opening exciting avenues for direct modulation of immune or tumor cells in situ, widening our strategies to remove cancer immunotherapy roadblocks. Here, we review current strategies for cancer immunotherapy, summarize technologies for generation of immune cells by cell fate reprogramming as well as highlight the future potential of inducing these unique cell identities in vivo, providing new and exciting tools for the fast-paced field of cancer immunotherapy.

Stem Cells as a Source of Pancreatic Cells for Production of 3D Bioprinted Bionic Pancreas in the Treatment of Type 1 Diabetes

Type 1 diabetes (T1D) is the third most common autoimmune disease which develops due to genetic and environmental risk factors. Often, intensive insulin therapy is insufficient, and patients require a pancreas or pancreatic islets transplant. However, both solutions are associated with many possible complications, including graft rejection. The best approach seems to be a donor-independent T1D treatment strategy based on human stem cells cultured in vitro and differentiated into insulin and glucagon-producing cells (β and α cells, respectively). Both types of cells can then be incorporated into the bio-ink used for 3D printing of the bionic pancreas, which can be transplanted into T1D patients to restore glucose homeostasis. The aim of this review is to summarize current knowledge about stem cells sources and their transformation into key pancreatic cells. Last, but not least, we comment on possible solutions of post-transplant immune response triggered stem cell-derived pancreatic cells and their potential control mechanisms.

REST Inhibits Direct Reprogramming of Pancreatic Exocrine to Endocrine Cells by Preventing PDX1-Mediated Activation of Endocrine Genes

The emerging appreciation of plasticity among pancreatic lineages has created interest in harnessing cellular reprogramming for β cell replacement therapy of diabetes. Current reprogramming methodologies are inefficient, largely because of a limited understanding of the underlying mechanisms. Using an in vitro reprogramming system, we reveal the transcriptional repressor RE-1 silencing transcription factor (REST) as a barrier for β cell gene expression in the reprogramming of pancreatic exocrine cells. We observe that REST-bound loci lie adjacent to the binding sites of multiple key β cell transcription factors, including PDX1. Accordingly, a loss of REST function combined with PDX1 expression results in the synergistic activation of endocrine genes. This is accompanied by increased histone acetylation and PDX1 binding at endocrine gene loci. Collectively, our data identify a mechanism for REST activity involving the prevention of PDX1-mediated activation of endocrine genes and uncover REST downregulation and the resulting chromatin alterations as key events in β cell reprogramming.

Islet Epigenetic Impacts on β-Cell Identity and Function

The development and maintenance of differentiation is vital to the function of mature cells. Terminal differentiation is achieved by locking in the expression of genes essential for the function of those cells. Gene expression and its memory through generations of cell division is controlled by transcription factors and a host of epigenetic marks. In type 2 diabetes, β cells have altered gene expression compared to controls, accompanied by altered chromatin marks. Mutations, diet, and environment can all disrupt the implementation and preservation of the distinctive β-cell transcriptional signature. Understanding of the full complement of genomic control in β cells is still nascent. This article describes the known effects of histone marks and variants, DNA methylation, how they are regulated in the β cell, and how they affect cell-fate specification, maintenance, and lineage propagation. © 2021 American Physiological Society. Compr Physiol 11:1-18, 2021.

Scrt1, a transcriptional regulator of β-cell proliferation identified by differential chromatin accessibility during islet maturation

Glucose-induced insulin secretion, a hallmark of mature β-cells, is achieved after birth and is preceded by a phase of intense proliferation. These events occurring in the neonatal period are decisive for establishing an appropriate functional β-cell mass that provides the required insulin throughout life. However, key regulators of gene expression involved in functional maturation of β-cells remain to be elucidated. Here, we addressed this issue by mapping open chromatin regions in newborn versus adult rat islets using the ATAC-seq assay. We obtained a genome-wide picture of chromatin accessible sites (~ 100,000) among which 20% were differentially accessible during maturation. An enrichment analysis of transcription factor binding sites identified a group of transcription factors that could explain these changes. Among them, Scrt1 was found to act as a transcriptional repressor and to control β-cell proliferation. Interestingly, Scrt1 expression was controlled by the transcriptional repressor RE-1 silencing transcription factor (REST) and was increased in an in vitro reprogramming system of pancreatic exocrine cells to β-like cells. Overall, this study led to the identification of several known and unforeseen key transcriptional events occurring during β-cell maturation. These findings will help defining new strategies to induce the functional maturation of surrogate insulin-producing cells.

Direct cell reprogramming: approaches, mechanisms and progress

The reprogramming of somatic cells with defined factors, which converts cells from one lineage into cells of another, has greatly reshaped our traditional views on cell identity and cell fate determination. Direct reprogramming (also known as transdifferentiation) refers to cell fate conversion without transitioning through an intermediary pluripotent state. Given that the number of cell types that can be generated by direct reprogramming is rapidly increasing, it has become a promising strategy to produce functional cells for therapeutic purposes. This Review discusses the evolution of direct reprogramming from a transcription factor-based method to a small-molecule-driven approach, the recent progress in enhancing reprogrammed cell maturation, and the challenges associated with in vivo direct reprogramming for translational applications. It also describes our current understanding of the molecular mechanisms underlying direct reprogramming, including the role of transcription factors, epigenetic modifications, non-coding RNAs, and the function of metabolic reprogramming, and highlights novel insights gained from single-cell omics studies.

Debates in Pancreatic Beta Cell Biology: Proliferation Versus Progenitor Differentiation and Transdifferentiation in Restoring β Cell Mass

In all forms of diabetes, β cell mass or function is reduced and therefore the capacity of the pancreatic cells for regeneration or replenishment is a critical need. Diverse lines of research have shown the capacity of endocrine as well as acinar, ductal and centroacinar cells to generate new β cells. Several experimental approaches using injury models, pharmacological or genetic interventions, isolation and in vitro expansion of putative progenitors followed by transplantations or a combination thereof have suggested several pathways for β cell neogenesis or regeneration. The experimental results have also generated controversy related to the limitations and interpretation of the experimental approaches and ultimately their physiological relevance, particularly when considering differences between mouse, the primary animal model, and human. As a result, consensus is lacking regarding the relative importance of islet cell proliferation or progenitor differentiation and transdifferentiation of other pancreatic cell types in generating new β cells. In this review we summarize and evaluate recent experimental approaches and findings related to islet regeneration and address their relevance and potential clinical application in the fight against diabetes.

Pancreatic and duodenal homeobox-1 in pancreatic ductal adenocarcinoma and diabetes mellitus

Diabetes mellitus and pancreatic ductal adenocarcinoma are two common diseases worldwidely which are both derived from different components of pancreas. The pancreatic and duodenal homeobox-1 (PDX1) is an essential transcription factor for the early development of pancreas that is required for the differentiation of all pancreatic cell lineages. Current evidence suggests an important role of PDX1 in both the origin and progression of pancreatic diseases. In this review, we discussed recent studies of PDX1 in diabetes mellitus and pancreatic cancer, and the therapeutic strategies derived from this transcription factor.

Pancreas-on-a-Chip Technology for Transplantation Applications

PURPOSE OF REVIEW

Human pancreas-on-a-chip (PoC) technology is quickly advancing as a platform for complex in vitro modeling of islet physiology. This review summarizes the current progress and evaluates the possibility of using this technology for clinical islet transplantation.

RECENT FINDINGS

PoC microfluidic platforms have mainly shown proof of principle for long-term culturing of islets to study islet function in a standardized format. Advancement in microfluidic design by using imaging-compatible biomaterials and biosensor technology might provide a novel future tool for predicting islet transplantation outcome. Progress in combining islets with other tissue types gives a possibility to study diabetic interventions in a minimal equivalent in vitro environment. Although the field of PoC is still in its infancy, considerable progress in the development of functional systems has brought the technology on the verge of a general applicable tool that may be used to study islet quality and to replace animal testing in the development of diabetes interventions.

Advances and complications of regenerative medicine in diabetes therapy

The rapid development of technologies in regenerative medicine indicates clearly that their common application is not a matter of if, but of when. However, the regeneration of beta-cells for diabetes patients remains a complex challenge due to the plurality of related problems. Indeed, the generation of beta-cells masses expressing marker genes is only a first step, with maintaining permanent insulin secretion, their protection from the immune system and avoiding pathological modifications in the genome being the necessary next developments. The prospects of regenerative medicine in diabetes therapy were promoted by the emergence of promising results with embryonic stem cells (ESCs). Their pluripotency and proliferation in an undifferentiated state during culture have ensured the success of ESCs in regenerative medicine. The discovery of induced pluripotent stem cells (iPSCs) derived from the patients’ own mesenchymal cells has provided further hope for diabetes treatment. Nonetheless, the use of stem cells has significant limitations related to the pluripotent stage, such as the risk of development of teratomas. Thus, the direct conversion of mature cells into beta-cells could address this issue. Recent studies have shown the possibility of such transdifferentiation and have set trends for regeneration medicine, directed at minimizing genome modifications and invasive procedures. In this review, we will discuss the published results of beta-cell regeneration and the advantages and disadvantages illustrated by these experiments.

Protocol for Studying Reprogramming of Mouse Pancreatic Acinar Cells to β-like Cells

The potential of reprogrammed β cells derived from pancreatic exocrine cells to treat diabetes has been demonstrated in animal models. However, the precise mechanisms and regulators involved in this process are not clear. Here, we describe a method that allows mechanistic studies of this process in primary exocrine cultures using adenoviral expression vectors. This rapid 5-day protocol, provides the researcher with a highly controlled experimental system in which the effects of different compounds or genetic manipulations can be studied. For complete details on the use and execution of this protocol, please refer to Elhanani et al. (2020).

Understanding generation and regeneration of pancreatic β cells from a single-cell perspective

Understanding the mechanisms that underlie the generation and regeneration of β cells is crucial for developing treatments for diabetes. However, traditional research methods, which are based on populations of cells, have limitations for defining the precise processes of β-cell differentiation and trans-differentiation, and the associated regulatory mechanisms. The recent development of single-cell technologies has enabled re-examination of these processes at a single-cell resolution to uncover intermediate cell states, cellular heterogeneity and molecular trajectories of cell fate specification. Here, we review recent advances in understanding β-cell generation and regeneration, in vivo and in vitro, from single-cell technologies, which could provide insights for optimization of diabetes therapy strategies.

Organoids from the Human Fetal and Adult Pancreas

PURPOSE OF REVIEW

Novel 3D organoid culture techniques have enabled long-term expansion of pancreatic tissue. This review comprehensively summarizes and evaluates the applications of primary tissue-derived pancreatic organoids in regenerative studies, disease modelling, and personalized medicine.

RECENT FINDINGS

Organoids derived from human fetal and adult pancreatic tissue have been used to study pancreas development and repair. Generated adult human pancreatic organoids harbor the capacity for clonal expansion and endocrine cell formation. In addition, organoids have been generated from human pancreatic ductal adenocarcinoma in order to study tumor behavior and assess drug responses. Pancreatic organoids constitute an important translational bridge between in vitro and in vivo models, enhancing our understanding of pancreatic cell biology. Current applications for pancreatic organoid technology include studies on tissue regeneration, disease modelling, and drug screening.

Recent advances in organoid culture for insulin production and diabetes therapy: methods and challenges

Breakthroughs in stem cell technology have contributed to disease modeling and drug screening via organoid technology. Organoid are defined as three-dimensional cellular aggregations derived from adult tissues or stem cells. They recapitulate the intricate pattern and functionality of the original tissue. Insulin is secreted mainly by the pancreatic β cells. Large-scale production of insulin-secreting β cells is crucial for diabetes therapy. Here, we provide a brief overview of organoids and focus on recent advances in protocols for the generation of pancreatic islet organoids from pancreatic tissue or pluripotent stem cells for insulin secretion. The feasibility and limitations of organoid cultures derived from stem cells for insulin production will be described. As the pancreas and gut share the same embryological origin and produce insulin, we will also discuss the possible application of gut organoids for diabetes therapy. Better understanding of the challenges associated with the current protocols for organoid culture facilitates development of scalable organoid cultures for applications in biomedicine.

Impelling force and current challenges by chemicals in somatic cell reprogramming and expansion beyond hepatocytes

In the field of regenerative medicine, generating numerous transplantable functional cells in the laboratory setting on a large scale is a major challenge. However, the in vitro maintenance and expansion of terminally differentiated cells are challenging because of the lack of specific environmental and intercellular signal stimulations, markedly hindering their therapeutic application. Remarkably, the generation of stem/progenitor cells or functional cells with effective proliferative potential is markedly in demand for disease modeling, cell-based transplantation, and drug discovery. Despite the potent genetic manipulation of transcription factors, integration-free chemically defined approaches for the conversion of somatic cell fate have garnered considerable attention in recent years. This review aims to summarize the progress thus far and discuss the advantages, limitations, and challenges of the impact of full chemicals on the stepwise reprogramming of pluripotency, direct lineage conversion, and direct lineage expansion on somatic cells. Owing to the current chemical-mediated induction, reprogrammed pluripotent stem cells with reproducibility difficulties, and direct lineage converted cells with marked functional deficiency, it is imperative to generate the desired cell types directly by chemically inducing their potent proliferation ability through a lineage-committed progenitor state, while upholding the maturation and engraftment capacity posttransplantation in vivo. Together with the comprehensive understanding of the mechanism of chemical drives, as well as the elucidation of specificity and commonalities, the precise manipulation of the expansion for diverse functional cell types could broaden the available cell sources and enhance the cellular function for clinical application in future.

Recent advances in organoid culture for insulin production and diabetes therapy: methods and challenges

Breakthroughs in stem cell technology have contributed to disease modeling and drug screening via organoid technology. Organoid are defined as three-dimensional cellular aggregations derived from adult tissues or stem cells. They recapitulate the intricate pattern and functionality of the original tissue. Insulin is secreted mainly by the pancreatic β cells. Large-scale production of insulin-secreting β cells is crucial for diabetes therapy. Here, we provide a brief overview of organoids and focus on recent advances in protocols for the generation of pancreatic islet organoids from pancreatic tissue or pluripotent stem cells for insulin secretion. The feasibility and limitations of organoid cultures derived from stem cells for insulin production will be described. As the pancreas and gut share the same embryological origin and produce insulin, we will also discuss the possible application of gut organoids for diabetes therapy. Better understanding of the challenges associated with the current protocols for organoid culture facilitates development of scalable organoid cultures for applications in biomedicine. [BMB Reports 2019; 52(5): 295-303].

Reprogramming Cells to Make Insulin

Type 1 diabetes is a disease characterized by the destruction of insulin-secreting β-cells in the pancreas. Individuals are treated for this disease with lifelong insulin replacement. However, one attractive treatment possibility is to reprogram an individual’s endogenous cells to acquire the ability to secrete insulin, essentially replacing destroyed β-cells. Herein, we review the literature on the topic of reprogramming endodermal cells to produce insulin.

Direct cellular reprogramming and inner ear regeneration

INTRODUCTION

Sound is integral to communication and connects us to the world through speech and music. Cochlear hair cells are essential for converting sounds into neural impulses. However, these cells are highly susceptible to damage from an array of factors, resulting in degeneration and ultimately irreversible hearing loss in humans. Since the discovery of hair cell regeneration in birds, there have been tremendous efforts to identify therapies that could promote hair cell regeneration in mammals.

AREAS COVERED

Here, we will review recent studies describing spontaneous hair cell regeneration and direct cellular reprograming as well as other factors that mediate mammalian hair cell regeneration.

EXPERT OPINION

Numerous combinatorial approaches have successfully reprogrammed non-sensory supporting cells to form hair cells, albeit with limited efficacy and maturation. Studies on epigenetic regulation and transcriptional network of hair cell progenitors may accelerate discovery of more promising reprogramming regimens.

The microRNA and the perspectives of miR-302

MiRNAs are naturally occurring, small, non-coding RNA molecules that post-transcriptionally regulate the expression of a large number of genes involved in various biological processes, either through mRNA degradation or through translation inhibition. MiRNAs play important roles in many aspects of physiology and pathology throughout the body, particularly in cancer, which have made miRNAs attractive tools and targets for translational research. The types of non-coding RNAs, biogenesis of miRNAs, circulating miRNAs, and direct delivery of miRNA were briefly reviewed. As a case of point, the role and perspective of miR-302, a family of ES-specific miRNA, on cancer, iPSCs, heart disease were presented.

Single-cell analyses of human islet cells reveal de-differentiation signatures

Human pancreatic islets containing insulin-secreting β-cells are notoriously heterogeneous in cell composition. Since β-cell failure is the root cause of diabetes, understanding this heterogeneity is of paramount importance. Recent reports have cataloged human islet transcriptome but not compared single β-cells in detail. Here, we scrutinized ex vivo human islet cells from healthy donors and show that they exhibit de-differentiation signatures. Using single-cell gene expression and immunostaining analyses, we found healthy islet cells to contain polyhormonal transcripts, and INS+ cells to express decreased levels of β-cell genes but high levels of progenitor markers. Rare cells that are doubly positive for progenitor markers/exocrine signatures, and endocrine/exocrine hormones were also present. We conclude that ex vivo human islet cells are plastic and can possibly de-/trans-differentiate across pancreatic cell fates, partly accounting for β-cell functional decline once isolated. Therefore, stabilizing β-cell identity upon isolation may improve its functionality.

Potentials of Cellular Reprogramming as a Novel Strategy for Neuroregeneration

Cellular reprogramming technology holds great potential for tissue repair and regeneration to replace cells that are lost due to diseases or injuries. In addition to the landmark discovery of induced pluripotent stem cells, advances in cellular reprogramming allow the direct lineage conversion of one somatic cell type to another using defined transcription factors. This direct reprogramming technology represents a rapid way to generate target cells in the laboratory, which can be used for transplantation and studies of biology and diseases. More importantly, recent work has demonstrated the exciting application of direct reprogramming to stimulate regeneration in vivo, providing an alternative approach to transplantation of donor cells. Here, we provide an overview of the underlying concept of using cellular reprogramming to convert cell fates and discuss the current advances in cellular reprogramming both in vitro and in vivo, with particular focuses on the neural and retinal systems. We also discuss the potential of in vivo reprogramming in regenerative medicine, the challenges and potential solutions to translate this technology to the clinic.

Neurogenin3 phosphorylation controls reprogramming efficiency of pancreatic ductal organoids into endocrine cells

β-cell replacement has been proposed as an effective treatment for some forms of diabetes, and in vitro methods for β-cell generation are being extensively explored. A potential source of β-cells comes from fate conversion of exocrine pancreatic cells into the endocrine lineage, by overexpression of three regulators of pancreatic endocrine formation and β-cell identity, Ngn3, Pdx1 and MafA. Pancreatic ductal organoid cultures have recently been developed that can be expanded indefinitely, while maintaining the potential to differentiate into the endocrine lineage. Here, using mouse pancreatic ductal organoids, we see that co-expression of Ngn3, Pdx1 and MafA are required and sufficient to generate cells that express insulin and resemble β-cells transcriptome-wide. Efficiency of β-like cell generation can be significantly enhanced by preventing phosphorylation of Ngn3 protein and further augmented by conditions promoting differentiation. Taken together, our new findings underline the potential of ductal organoid cultures as a source material for generation of β-like cells and demonstrate that post-translational regulation of reprogramming factors can be exploited to enhance β-cell generation.

Regulation of glucose and lipid metabolism by the pancreatic and extra-pancreatic actions of taurine

The beneficial actions of L-taurine (Tau) against glucose intolerance, obesity, type 2 diabetes (T2D), and non-alcoholic fat liver disease (NAFLD) have been linked to its antioxidant and anti-inflammatory effects, which ameliorate tissue insulin sensitivity. Importantly, there are several lines of evidence that indicate a direct action of Tau on the endocrine pancreas to regulate the secretion and paracrine actions of insulin, glucagon, and somatostatin. Furthermore, Tau can also ameliorate glucose metabolism through the enhancement of insulin signaling. However, some of the benefits of Tau upon intermediary metabolism may manifest via considerable antagonism of the action of insulin. Therefore, this review discusses the mechanisms of action by which Tau may regulate endocrine pancreatic morphofunction, and glucose and lipid homeostasis.