In vivo reprogramming of adult pancreatic exocrine cells to beta-cells. Nature. 2008;455:627-632. [PMID: 18754011 DOI: 10.1038/nature07314]

Engineered tools to study endocrine dysfunction of pancreas

Pancreas, a vital organ with intricate endocrine and exocrine functions, is central to the regulation of the body's glucose levels and digestive processes. Disruptions in its endocrine functions, primarily regulated by islets of Langerhans, can lead to debilitating diseases such as diabetes mellitus. Murine models of pancreatic dysfunction have contributed significantly to the understanding of insulitis, islet-relevant immunological responses, and the optimization of cell therapies. However, genetic differences between mice and humans have severely limited their clinical translational relevance. Recent advancements in tissue engineering and microfabrication have ushered in a new era of in vitro models that offer a promising solution. This paper reviews the state-of-the-art engineered tools designed to study endocrine dysfunction of the pancreas. Islet on a chip devices that allow precise control of various culture conditions and noninvasive readouts of functional outcomes have led to the generation of physiomimetic niches for primary and stem cell derived islets. Live pancreatic slices are a new experimental tool that could more comprehensively recapitulate the complex cellular interplay between the endocrine and exocrine parts of the pancreas. Although a powerful tool, live pancreatic slices require more complex control over their culture parameters such as local oxygenation and continuous removal of digestive enzymes and cellular waste products for maintaining experimental functionality over long term. The combination of islet-immune and slice on chip strategies can guide the path toward the next generation of pancreatic tissue modeling for better understanding and treatment of endocrine pancreatic dysfunctions.

In vivo dendritic cell reprogramming for cancer immunotherapy

Immunotherapy can lead to long-term survival for some cancer patients, yet generalized success has been hampered by insufficient antigen presentation and exclusion of immunogenic cells from the tumor microenvironment. Here, we developed an approach to reprogram tumor cells in vivo by adenoviral delivery of the transcription factors PU.1, IRF8, and BATF3, which enabled them to present antigens as type 1 conventional dendritic cells. Reprogrammed tumor cells remodeled their tumor microenvironment, recruited, and expanded polyclonal cytotoxic T cells; induced tumor regressions; and established long-term systemic immunity in multiple mouse melanoma models. In human tumor spheroids and xenografts, reprogramming to immunogenic dendritic-like cells progressed independently of immunosuppression, which usually limits immunotherapy. Our study paves the way for human clinical trials of in vivo immune cell reprogramming for cancer immunotherapy.

Alpha- to Beta-Cell Transdifferentiation in Neonatal Compared with Adult Mouse Pancreas in Response to a Modest Reduction in Beta-Cells Using Streptozotocin

Following the near-total depletion of pancreatic beta-cells with streptozotocin (STZ), a partial recovery of beta-cell mass (BCM) can occur, in part due to the alpha- to beta-cell transdifferentiation with an intermediary insulin/glucagon bi-hormonal cell phenotype. However, human type 2 diabetes typically involves only a partial reduction in BCM and it is not known if recovery after therapeutic intervention involves islet cell transdifferentiation, or how this varies with age. Here, we used transgenic mouse models to examine if islet cell transdifferentiation contributes to BCM recovery following only a partial depletion of BCM. Cell lineage tracing was employed using Glucagon-Cre/yellow fluorescent protein (YFP) transgenic mice treated with STZ (25 mg/kg-neonates; 70 mg/kg-adults) or vehicle alone on 3 consecutive days. Mice were euthanized 2-30 days later with a prior glucose tolerance test on day 30, and immunofluorescence histology performed on the pancreata. Beta-cell abundance was reduced by 30-40% two days post STZ in both neonates and adults, and subsequently partially recovered in adult but not neonatal mice. Glucose tolerance recovered in adult females, but not in males or neonates. Bi-hormonal cell abundance increased 2-3-fold in STZ-treated mice vs. controls in both neonates and adults, as did transdifferentiated cells expressing insulin and the YFP lineage tag, but not glucagon. Transdifferentiated cell presence was an order of magnitude lower than that of bi-hormonal cells. We conclude that alpha- to beta-cell transdifferentiation occurs in mice following only a moderate depletion in BCM, and that this was accompanied by a partial recovery of BCM in adults.

The Progress and Promise of Lineage Reprogramming Strategies for Liver Regeneration

The liver exhibits remarkable regenerative capacity. However, the limited ability of primary human hepatocytes to proliferate in vitro, combined with a compromised regenerative capacity induced by pathological conditions in vivo, presents significant obstacles to effective liver regeneration following liver injuries and diseases. Developing strategies to compensate for the loss of endogenous hepatocytes is crucial for overcoming these challenges, and this remains an active area of investigation. Lineage reprogramming, the process of directly converting one cell type into another bypassing the intermediate pluripotent state, has emerged as a promising method for generating specific cell types for therapeutic purposes in regenerative medicine. Here, we discuss the recent progress and emergent technologies in lineage reprogramming into hepatic cells, and their potential applications in enhancing liver regeneration or treating liver disease models. We also address controversies and challenges that confront this field.

Pregnancy-induced metabolic reprogramming and regenerative responses to pro-aging stresses

Pregnancy is associated with physiological adaptations that affect virtually all organs, enabling the mother to support the growing fetus and placenta while withstanding the demands of pregnancy. As a result, mammalian pregnancy is a unique state that exerts paradoxical effects on maternal health. On one hand, the metabolic stress induced by pregnancy can accelerate aging and functional decline in organs. On the other hand, pregnancy activates metabolic programming and tissue regenerative responses that can reverse age-related impairments. In this sense, the oocyte-to-blastocyst transition is not the only physiological reprogramming event in the mammalian body, as pregnancy-induced regeneration could constitute a second physiological reprogramming event. Here, we review findings on how pregnancy dualistically leads to aging and rejuvenation in the maternal body.

Differential contributions of G protein- or arrestin subtype-mediated signalling underlie urocortin 3-induced somatostatin secretion in pancreatic δ cells

BACKGROUND AND PURPOSE

Pancreatic islets are modulated by cross-talk among different cell types and paracrine signalling plays important roles in maintaining glucose homeostasis. Urocortin 3 (UCN3) secreted by pancreatic β cells activates the CRF2 receptor (CRF2R) and downstream pathways mediated by different G protein or arrestin subtypes in δ cells to cause somatostatin (SST) secretion, and constitutes an important feedback circuit for glucose homeostasis.

EXPERIMENTAL APPROACH

Here, we used Arrb1-/-, Arrb2-/-, Gsfl/fl and Gqfl/fl knockout mice, the G11-shRNA-GFPfl/fl lentivirus, as well as functional assays and pharmacological characterization to study how the coupling of Gs, G11 and β-arrestin1 to CRF2R contributed to UCN3-induced SST secretion in pancreatic δ cells.

KEY RESULTS

Our study showed that CRF2R coupled to a panel of G protein and arrestin subtypes in response to UCN3 engagement. While RyR3 phosphorylation by PKA at the S156, S2706 and S4697 sites may underlie the Gs-mediated UCN3- CRF2R axis for SST secretion, the interaction of SYT1 with β-arrestin1 is also essential for efficient SST secretion downstream of CRF2R. The specific expression of the transcription factor Stat6 may contribute to G11 expression in pancreatic δ cells. Furthermore, we found that different UCN3 concentrations may have distinct effects on glucose homeostasis, and these effects may depend on different CRF2R downstream effectors.

CONCLUSIONS AND IMPLICATIONS

Collectively, our results provide a landscape view of signalling mediated by different G protein or arrestin subtypes downstream of paracrine UCN3- CRF2R signalling in pancreatic β-δ-cell circuits, which may facilitate the understanding of fine-tuned glucose homeostasis networks.

Advances in neuronal reprogramming for neurodegenerative diseases: Strategies, controversies, and opportunities

Neuronal death is often observed in central nervous system injuries and neurodegenerative diseases. The mammalian central nervous system manifests limited neuronal regeneration capabilities, and traditional cell therapies are limited in their potential applications due to finite cell sources and immune rejection. Neuronal reprogramming has emerged as a novel technology, in which non-neuronal cells (e.g. glial cells) are transdifferentiated into mature neurons. This process results in relatively minimal immune rejection. The present review discuss the latest progress in this cutting-edge field, including starter cell selection, innovative technical strategies and methods of neuronal reprogramming for neurodegenerative diseases, as well as the potential problems and controversies. The further development of neuronal reprogramming technology may pave the way for novel therapeutic strategies in the treatment of neurodegenerative diseases.

β-cell neogenesis: A rising star to rescue diabetes mellitus

BACKGROUND

Diabetes Mellitus (DM), a chronic metabolic disease characterized by elevated blood glucose, is caused by various degrees of insulin resistance and dysfunctional insulin secretion, resulting in hyperglycemia. The loss and failure of functional β-cells are key mechanisms resulting in type 1 diabetes mellitus (T1DM) and type 2 diabetes mellitus (T2DM).

AIM OF REVIEW

Elucidating the underlying mechanisms of β-cell failure, and exploring approaches for β-cell neogenesis to reverse β-cell dysfunction may provide novel strategies for DM therapy.

KEY SCIENTIFIC CONCEPTS OF REVIEW

Emerging studies reveal that genetic susceptibility, endoplasmic reticulum (ER) stress, oxidative stress, islet inflammation, and protein modification linked to multiple signaling pathways contribute to DM pathogenesis. Over the past few years, replenishing functional β-cell by β-cell neogenesis to restore the number and function of pancreatic β-cells has remarkably exhibited a promising therapeutic approach for DM therapy. In this review, we provide a comprehensive overview of the underlying mechanisms of β-cell failure in DM, highlight the effective approaches for β-cell neogenesis, as well as discuss the current clinical and preclinical agents research advances of β-cell neogenesis. Insights into the challenges of translating β-cell neogenesis into clinical application for DM treatment are also offered.

Targeting β-Cell Plasticity: A Promising Approach for Diabetes Treatment

The β-cells within the pancreas play a pivotal role in insulin production and secretion, responding to fluctuations in blood glucose levels. However, factors like obesity, dietary habits, and prolonged insulin resistance can compromise β-cell function, contributing to the development of Type 2 Diabetes (T2D). A critical aspect of this dysfunction involves β-cell dedifferentiation and transdifferentiation, wherein these cells lose their specialized characteristics and adopt different identities, notably transitioning towards progenitor or other pancreatic cell types like α-cells. This process significantly contributes to β-cell malfunction and the progression of T2D, often surpassing the impact of outright β-cell loss. Alterations in the expressions of specific genes and transcription factors unique to β-cells, along with epigenetic modifications and environmental factors such as inflammation, oxidative stress, and mitochondrial dysfunction, underpin the occurrence of β-cell dedifferentiation and the onset of T2D. Recent research underscores the potential therapeutic value for targeting β-cell dedifferentiation to manage T2D effectively. In this review, we aim to dissect the intricate mechanisms governing β-cell dedifferentiation and explore the therapeutic avenues stemming from these insights.

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.

Salivary Gland Tissue Recombination Can Modify Cell Fate

Although mesenchyme is essential for inducing the epithelium of ectodermal organs, its precise role in organ-specific epithelial fate determination remains poorly understood. To elucidate the roles of tissue interactions in cellular differentiation, we performed single-cell RNA sequencing and imaging analyses on recombined tissues, where mesenchyme and epithelium were switched ex vivo between two types of embryonic mouse salivary glands: the parotid gland (a serous gland) and the submandibular gland (a predominantly mucous gland). We found partial induction of molecules that define gland-specific acinar and myoepithelial cells in recombined salivary epithelium. The parotid epithelium recombined with submandibular mesenchyme began to express mucous acinar genes not intrinsic to the parotid gland. While myoepithelial cells do not normally line parotid acini, newly induced myoepithelial cells densely populated recombined parotid acini. However, mucous acinar and myoepithelial markers continued to be expressed in submandibular epithelial cells recombined with parotid mesenchyme. Consequently, some epithelial cells appeared to be plastic, such that their fate could still be modified in response to mesenchymal signaling, whereas other epithelial cells appeared to be already committed to a specific fate. We also discovered evidence for bidirectional induction: transcriptional changes were observed not only in the epithelium but also in the mesenchyme after heterotypic tissue recombination. For example, parotid epithelium induced the expression of muscle-related genes in submandibular fibroblasts that began to mimic parotid fibroblast gene expression. These studies provide the first comprehensive unbiased molecular characterization of tissue recombination approaches exploring the regulation of cell fate.

Gene therapy targeting key beta cell regulators as a potential intervention for diabetes

In this Comment, Wing Yan So and Weiping Han discuss the recent achievements and therapeutic potential of gene therapy targeting beta cell regulators for the treatment of diabetes.

Neuronal conversion from glia to replenish the lost neurons

ABSTRACT

Neuronal injury, aging, and cerebrovascular and neurodegenerative diseases such as cerebral infarction, Alzheimer's disease, Parkinson's disease, frontotemporal dementia, amyotrophic lateral sclerosis, and Huntington's disease are characterized by significant neuronal loss. Unfortunately, the neurons of most mammals including humans do not possess the ability to self-regenerate. Replenishment of lost neurons becomes an appealing therapeutic strategy to reverse the disease phenotype. Transplantation of pluripotent neural stem cells can supplement the missing neurons in the brain, but it carries the risk of causing gene mutation, tumorigenesis, severe inflammation, and obstructive hydrocephalus induced by brain edema. Conversion of neural or non-neural lineage cells into functional neurons is a promising strategy for the diseases involving neuron loss, which may overcome the above-mentioned disadvantages of neural stem cell therapy. Thus far, many strategies to transform astrocytes, fibroblasts, microglia, Müller glia, NG2 cells, and other glial cells to mature and functional neurons, or for the conversion between neuronal subtypes have been developed through the regulation of transcription factors, polypyrimidine tract binding protein 1 (PTBP1), and small chemical molecules or are based on a combination of several factors and the location in the central nervous system. However, some recent papers did not obtain expected results, and discrepancies exist. Therefore, in this review, we discuss the history of neuronal transdifferentiation, summarize the strategies for neuronal replenishment and conversion from glia, especially astrocytes, and point out that biosafety, new strategies, and the accurate origin of the truly converted neurons in vivo should be focused upon in future studies. It also arises the attention of replenishing the lost neurons from glia by gene therapies such as up-regulation of some transcription factors or down-regulation of PTBP1 or drug interference therapies.

Diabetes treatment by conversion of gut epithelial cells to insulin-producing cells

Insulin-deficient (type 1) diabetes is treated by providing insulin to maintain euglycemia. The current standard of care is a quasi-closed loop integrating automated insulin delivery with a continuous glucose monitoring sensor. Cell replacement technologies are advancing as an alternative treatment and have been tested as surrogates to cadaveric islets in transplants. In addition, immunomodulatory treatments to delay the onset of type 1 diabetes in high-risk (stage 2) individuals have gained regulatory approval. We have pioneered a cell conversion approach to restore insulin production through pharmacological conversion of intestinal epithelial cells into insulin-producing cells. We have advanced this approach along a translational trajectory through the discovery of small molecule forkhead box protein O1 inhibitors. When administered to different rodent models of insulin-deficient diabetes, these inhibitors have resulted in robust glucose-lowering responses and generation of insulin-producing cells in the gut epithelium. We review past work and delineate a path to human clinical trials.

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.

Direct reprogramming of fibroblasts into functional hepatocytes via CRISPRa activation of endogenous Gata4 and Foxa3

BACKGROUND

The ability to generate functional hepatocytes without relying on donor liver organs holds significant therapeutic promise in the fields of regenerative medicine and potential liver disease treatments. Clustered regularly interspaced short palindromic repeats (CRISPR) activator (CRISPRa) is a powerful tool that can conveniently and efficiently activate the expression of multiple endogenous genes simultaneously, providing a new strategy for cell fate determination. The main purpose of this study is to explore the feasibility of applying CRISPRa for hepatocyte reprogramming and its application in the treatment of mouse liver fibrosis.

METHOD

The differentiation of mouse embryonic fibroblasts (MEFs) into functional induced hepatocyte-like cells (iHeps) was achieved by utilizing the CRISPRa synergistic activation mediator (SAM) system, which drove the combined expression of three endogenous transcription factors- Gata4, Foxa3 , and Hnf1a -or alternatively, the expression of two transcription factors, Gata4 and Foxa3 . In vivo , we injected adeno-associated virus serotype 6 (AAV6) carrying the CRISPRa SAM system into liver fibrotic Col1a1-CreER ; Cas9fl/fl mice, effectively activating the expression of endogenous Gata4 and Foxa3 in fibroblasts. The endogenous transcriptional activation of genes was confirmed using real-time quantitative polymerase chain reaction (RT-qPCR) and RNA-seq, and the morphology and characteristics of the induced hepatocytes were observed through microscopy. The level of hepatocyte reprogramming in vivo is detected by immunofluorescence staining, while the improvement of liver fibrosis is evaluated through Sirius red staining, alpha-smooth muscle actin (α-SMA) immunofluorescence staining, and blood alanine aminotransferase (ALT) examination.

RESULTS

Activation of only two factors, Gata4 and Foxa3 , via CRISPRa was sufficient to successfully induce the transformation of MEFs into iHeps. These iHeps could be expanded in vitro and displayed functional characteristics similar to those of mature hepatocytes, such as drug metabolism and glycogen storage. Additionally, AAV6-based delivery of the CRISPRa SAM system effectively induced the hepatic reprogramming from fibroblasts in mice with live fibrosis. After 8 weeks of induction, the reprogrammed hepatocytes comprised 0.87% of the total hepatocyte population in the mice, significantly reducing liver fibrosis.

CONCLUSION

CRISPRa-induced hepatocyte reprogramming may be a promising strategy for generating functional hepatocytes and treating liver fibrosis caused by hepatic diseases.

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.

PDX1, a transcription factor essential for organ differentiation, regulates SERCA-dependent Ca2+ homeostasis in sensory neurons

Pancreatic and duodenal homeobox 1 (PDX1) is a transcription factor required for the development and differentiation of the pancreas. Previous studies indicated that PDX1 expression was restricted to the gastrointestinal tract. Using a cre-dependent reporter, we observed PDX1-dependent expression of tdtomato (PDX1-tom) in a subpopulation of sensory nerves. Many of these PDX1-tom afferents expressed the neurofilament 200 protein and projected to the skin. Tdtomato-labeled terminals were associated with hair follicles in the form of longitudinal and circumferential lanceolate endings suggesting a role in tactile and proprioceptive perception. To begin to examine the functional significance of PDX1 in afferents, we used Fura-2 imaging to examine calcium (Ca2+) handling under naïve and nerve injury conditions. Neuropathic injury is associated with increased intracellular Ca2+ signaling that in part results from dysregulation of the sarco/endoplasmic reticulum calcium transport ATPase (SERCA). Here we demonstrate that under naïve conditions, PDX1 regulates expression of the SERCA2B isoform in sensory neurons. In response to infraorbital nerve injury, a significant reduction of PDX1 and SERCA2B expression and dysregulation of Ca2+ handling occurs in PDX1-tom trigeminal ganglia neurons. The identification of PDX1 expression in the somatosensory system and its regulation of SERCA2B and Ca2+ handling provide a new mechanism to explain pathological changes in primary afferents that may contribute to pain associated with nerve injury.

Loss-of-function of ALDH3B2 transdifferentiates human pancreatic duct cells into beta-like cells

Replenishment of pancreatic beta cells is a key to the cure for diabetes. Beta cells regeneration is achieved predominantly by self-replication especially in rodents, but it was also shown that pancreatic duct cells can transdifferentiate into beta cells. How pancreatic duct cells undergo transdifferentiated and whether we could manipulate the transdifferentiation to replenish beta cell mass is not well understood. Using a genome-wide CRISPR screen, we discovered that loss-of-function of ALDH3B2 is sufficient to transdifferentiate human pancreatic duct cells into functional beta-like cells. The transdifferentiated cells have significant increase in beta cell marker genes expression, secrete insulin in response to glucose, and reduce blood glucose when transplanted into diabetic mice. Our study identifies a novel gene that could potentially be targeted in human pancreatic duct cells to replenish beta cell mass for diabetes therapy.

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.

Harnessing beta cell regeneration biology for diabetes therapy

The pandemic scale of diabetes mellitus is alarming, its complications remain devastating, and current treatments still pose a major burden on those affected and on the healthcare system as a whole. As the disease emanates from the destruction or dysfunction of insulin-producing pancreatic β-cells, a real cure requires their restoration and protection. An attractive strategy is to regenerate β-cells directly within the pancreas; however, while several approaches for β-cell regeneration have been proposed in the past, clinical translation has proven challenging. This review scrutinizes recent findings in β-cell regeneration and discusses their potential clinical implementation. Hereby, we aim to delineate a path for innovative, targeted therapies to help shift from 'caring for' to 'curing' diabetes.

Pancreatic β-cell failure, clinical implications, and therapeutic strategies in type 2 diabetes

ABSTRACT

Pancreatic β-cell failure due to a reduction in function and mass has been defined as a primary contributor to the progression of type 2 diabetes (T2D). Reserving insulin-producing β-cells and hence restoring insulin production are gaining attention in translational diabetes research, and β-cell replenishment has been the main focus for diabetes treatment. Significant findings in β-cell proliferation, transdifferentiation, pluripotent stem cell differentiation, and associated small molecules have served as promising strategies to regenerate β-cells. In this review, we summarize current knowledge on the mechanisms implicated in β-cell dynamic processes under physiological and diabetic conditions, in which genetic factors, age-related alterations, metabolic stresses, and compromised identity are critical factors contributing to β-cell failure in T2D. The article also focuses on recent advances in therapeutic strategies for diabetes treatment by promoting β-cell proliferation, inducing non-β-cell transdifferentiation, and reprograming stem cell differentiation. Although a significant challenge remains for each of these strategies, the recognition of the mechanisms responsible for β-cell development and mature endocrine cell plasticity and remarkable advances in the generation of exogenous β-cells from stem cells and single-cell studies pave the way for developing potential approaches to cure diabetes.

Traditional and emerging strategies using hepatocytes for pancreatic regenerative medicine

Although pancreas and islet cell transplantation are the only ways to prevent the late complications of insulin-dependent diabetes, a shortage of donors is a major obstacle to tissue and organ transplantation. Stem cell therapy is an effective treatment for diabetes and other pancreatic-related diseases, which can be achieved by inducing their differentiation into insulin-secreting cells. The liver is considered an ideal source of pancreatic cells due to its similar developmental origin and strong regenerative ability as the pancreas. This article reviews the traditional and emerging strategies using hepatocytes for pancreatic regenerative medicine and evaluates their advantages and challenges. Gene reprogramming and chemical reprogramming technologies are traditional strategies with potential to improve the efficiency and specificity of cell reprogramming and promote the transformation of hepatocytes into islet cells. At the same time, organoid technology, as an emerging strategy, has received extensive attention. Biomaterials provide a three-dimensional culture microenvironment for cells, which helps improve cell survival and differentiation efficiency. In addition, clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 gene editing technology has brought new opportunities and challenges to the development of organoid technology.

Cell-fate conversion of intestinal cells in adult Drosophila midgut by depleting a single transcription factor

The manipulation of cell identity by reprograming holds immense potential in regenerative medicine, but is often limited by the inefficient acquisition of fully functional cells. This problem can potentially be resolved by better understanding the reprogramming process using in vivo genetic models, which are currently scarce. Here we report that both enterocytes (ECs) and enteroendocrine cells (EEs) in adult Drosophila midgut show a surprising degree of cell plasticity. Depleting the transcription factor Tramtrack in the differentiated ECs can initiate Prospero-mediated cell transdifferentiation, leading to EE-like cells. On the other hand, depletion of Prospero in the differentiated EEs can lead to the loss of EE-specific transcription programs and the gain of intestinal progenitor cell identity, allowing cell cycle re-entry or differentiation into ECs. We find that intestinal progenitor cells, ECs, and EEs have a similar chromatin accessibility profile, supporting the concept that cell plasticity is enabled by pre-existing chromatin accessibility with switchable transcription programs. Further genetic analysis with this system reveals that the NuRD chromatin remodeling complex, cell lineage confliction, and age act as barriers to EC-to-EE transdifferentiation. The establishment of this genetically tractable in vivo model should facilitate mechanistic investigation of cell plasticity at the molecular and genetic level.

Sendai virus is robust and consistent in delivering genes into human pancreatic cancer cells

Background

Pancreatic ductal adenocarcinoma (PDAC) is a highly intratumorally heterogeneous disease that includes several subtypes and is highly plastic. Effective gene delivery to all PDAC cells is essential for modulating gene expression and identifying potential gene-based therapeutic targets in PDAC. Most current gene delivery systems for pancreatic cells are optimized for islet or acinar cells. Lentiviral vectors are the current main gene delivery vectors for PDAC, but their transduction efficiencies vary depending on pancreatic cell type, and are especially poor for the classical subtype of PDAC cells from both primary tumors and cell lines.

Methods

We systemically compare transduction efficiencies of glycoprotein G of vesicular stomatitis virus (VSV-G)-pseudotyped lentiviral and Sendai viral vectors in human normal pancreatic ductal and PDAC cells.

Results

We find that the Sendai viral vector gives the most robust gene delivery efficiency regardless of PDAC cell type. Therefore, we propose using Sendai viral vectors to transduce ectopic genes into PDAC cells.

Direct reprogramming of non-limb fibroblasts to cells with properties of limb progenitors

The early limb bud consists of mesenchymal limb progenitors derived from the lateral plate mesoderm (LPM). The LPM also gives rise to the mesodermal components of the flank and neck. However, the cells at these other levels cannot produce the variety of cell types found in the limb. Taking advantage of a direct reprogramming approach, we find a set of factors (Prdm16, Zbtb16, and Lin28a) normally expressed in the early limb bud and capable of imparting limb progenitor-like properties to mouse non-limb fibroblasts. The reprogrammed cells show similar gene expression profiles and can differentiate into similar cell types as endogenous limb progenitors. The further addition of Lin41 potentiates the proliferation of the reprogrammed cells. These results suggest that these same four factors may play pivotal roles in the specification of endogenous limb progenitors.

Partial Reprogramming as a Method for Regenerating Neural Tissues in Aged Organisms

Aging causes numerous age-related diseases, leading the human species to death. Nevertheless, rejuvenating strategies based on cell epigenetic modifications are a possible approach to counteract disease progression while getting old. Cell reprogramming of adult somatic cells toward pluripotency ought to be a promising tool for age-related diseases. However, researchers do not have control over this process as cells lose their fate, and cause potential cancerous cells or unexpected cell phenotypes. Direct and partial reprogramming were introduced in recent years with distinctive applications. Although direct reprogramming makes cells lose their identity, it has various applications in regeneration medicine. Temporary and regulated in vivo overexpression of Yamanaka factors has been shown in several experimental contexts to be achievable and is used to rejuvenate mice models. This regeneration can be accomplished by altering the epigenetic adult cell signature to the signature of a younger cell. The greatest advantage of partial reprogramming is that this method does not allow cells to lose their identity when they are resetting their epigenetic clock. It is a regimen of short-term Oct3/4, Sox2, Klf4, and c-Myc expression in vivo that prevents full reprogramming to the pluripotent state and avoids both tumorigenesis and the presence of unwanted undifferentiated cells. We know that many neurological age-related diseases, such as Alzheimer's disease, stroke, dementia, and Parkinson's disease, are the main cause of death in the last decades of life. Therefore, scientists have a special tendency regarding neuroregeneration methods to increase human life expectancy.

Dynamics of cell-type transition mediated by epigenetic modifications

Maintaining tissue homeostasis requires appropriate regulation of stem cell differentiation. The Waddington landscape posits that gene circuits in a cell form a potential landscape of different cell types, wherein cells follow attractors of the probability landscape to develop into distinct cell types. However, how adult stem cells achieve a delicate balance between self-renewal and differentiation remains unclear. We propose that random inheritance of epigenetic states plays a pivotal role in stem cell differentiation and present a hybrid model of stem cell differentiation induced by epigenetic modifications. Our comprehensive model integrates gene regulation networks, epigenetic state inheritance, and cell regeneration, encompassing multi-scale dynamics ranging from transcription regulation to cell population. Through model simulations, we demonstrate that random inheritance of epigenetic states during cell divisions can spontaneously induce cell differentiation, dedifferentiation, and transdifferentiation. Furthermore, we investigate the influences of interfering with epigenetic modifications and introducing additional transcription factors on the probabilities of dedifferentiation and transdifferentiation, revealing the underlying mechanism of cell reprogramming. This in silico model provides valuable insights into the intricate mechanism governing stem cell differentiation and cell reprogramming and offers a promising path to enhance the field of regenerative medicine.

Current Advances in Corneal Stromal Stem Cell Biology and Therapeutic Applications

Corneal stromal stem cells (CSSCs) are of particular interest in regenerative ophthalmology, offering a new therapeutic target for corneal injuries and diseases. This review provides a comprehensive examination of CSSCs, exploring their anatomy, functions, and role in maintaining corneal integrity. Molecular markers, wound healing mechanisms, and potential therapeutic applications are discussed. Global corneal blindness, especially in more resource-limited regions, underscores the need for innovative solutions. Challenges posed by corneal defects, emphasizing the urgent need for advanced therapeutic interventions, are discussed. The review places a spotlight on exosome therapy as a potential therapy. CSSC-derived exosomes exhibit significant potential for modulating inflammation, promoting tissue repair, and addressing corneal transparency. Additionally, the rejuvenation potential of CSSCs through epigenetic reprogramming adds to the evolving regenerative landscape. The imperative for clinical trials and human studies to seamlessly integrate these strategies into practice is emphasized. This points towards a future where CSSC-based therapies, particularly leveraging exosomes, play a central role in diversifying ophthalmic regenerative medicine.

LncRNA Malat1 regulates iPSC-derived β-cell differentiation by targeting the miR-15b-5p/Ihh axis

BACKGROUND

Differentiation of induced pluripotent stem cells (iPSCs)-derived β-like cells is a novel strategy for treatment of type 1 diabetes. Elucidation of the regulatory mechanisms of long noncoding RNAs (lncRNAs) in β-like cells derived from iPSCs is important for understanding the development of the pancreas and pancreatic β-cells and may improve the quality of β-like cells for stem cell therapy.

METHODS

β-like cells were derived from iPSCs in a three-step protocol. RNA sequencing and bioinformatics analysis were carried out to screen the differentially expressed lncRNAs and identify the putative target genes separately. LncRNA Malat1 was chosen for further research. Series of loss and gain of functions experiments were performed to study the biological function of LncRNA Malat1. Quantitative real-time PCR (qRT-PCR), Western blot (WB) analysis and immunofluorescence (IF) staining were carried out to separately detect the functions of pancreatic β-cells at the mRNA and protein levels. Cytoplasmic and nuclear RNA fractionation and fluorescence in situ hybridization (FISH) were used to determine the subcellar location of lncRNA Malat1 in β-like cells. Enzyme-linked immunosorbent assays (ELISAs) were performed to examine the differentiation and insulin secretion of β-like cells after stimulation with different glucose concentrations. Structural interactions between lncRNA Malat1 and miR-15b-5p and between miR-15b-5p/Ihh were detected by dual luciferase reporter assays (LRAs).

RESULTS

We found that the expression of lncRNA Malat1 declined during differentiation, and overexpression (OE) of lncRNA Malat1 notably impaired the differentiation and maturation of β-like cells derived from iPSCs in vitro and in vivo. Most importantly, lncRNA Malat1 could function as a competing endogenous RNA (ceRNA) of miR-15b-5p to regulate the expression of Ihh according to bioinformatics prediction, mechanistic analysis and downstream experiments.

CONCLUSION

This study established an unreported regulatory network of lncRNA Malat1 and the miR-15b-5p/Ihh axis during the differentiation of iPSCs into β-like cells. In addition to acting as an oncogene promoting tumorigenesis, lncRNA Malat1 may be an effective and novel target for treatment of diabetes in the future.

Signaling Pathways in Trans-differentiation of Mesenchymal Stem Cells: Recent Advances

Mesenchymal stem cells are a group of multipotent cells that can be induced to differentiate into other cell types. The cells fate is decided by various signaling pathways, growth factors, and transcription factors in differentiation. The proper coordination of these factors will result in cell specification. MSCs are capable of being differentiated into osteogenic, chondrogenic, and adipogenic lineages. Different conditions induces the MSCs into particular phenotypes. The MSC trans-differentiation ensues as a response to environmental factors or due to circumstances that prove to favor trans-differentiation. Depending on the stage at which they are expressed, and the genetic alterations they undergo prior to their expression, transcription factors can accelerate the process of trans-differentiation. Further research has been conducted on the challenging aspect of MSCs being developed into non-mesenchymal lineage. The cells that are differentiated in this way maintain their stability even after being induced in animals. The recent advancements in the trans-differentiation capacities of MSCs on induction with chemicals, growth inducers, improved differentiation mediums, growth factors from plant extracts, and electrical stimulation are discussed in this paper. Signaling pathways have a great effect on MSCs trans-differentiation and they need to be better understood for their applications in therapeutic techniques. So, this paper tends to review the major signaling pathways that play a vital role in the trans-differentiation of MSC.

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.

In situ Reprogramming as a Pro-Angiogenic Inducer to Rescue Ischemic Tissues

Background

Enhanced regenerative therapeutic strategies are required to treat intractable ischemic heart disease.

Summary

Since the discovery of putative endothelial progenitor cells (EPCs) in 1997, many studies have focused on their extraction, ex vivo processing, and autotransplantation under ischemic conditions. Nonetheless, numerous randomized clinical trials involving thousands of patients have yielded only marginal treatment effects, highlighting the need for advances regarding insufficient dosage and complex ex vivo processing. The prevailing paradigm of cellular differentiation highlights the potential of direct cellular reprogramming, which paves the way for in situ reprogramming. In situ reprogramming holds the promise of significantly enhancing current therapeutic strategies, yet its success hinges on the precise targeting of candidate cells for reprogramming. In this context, the spleen emerges as a pivotal "in situ reprogramming hub," owing to its dual function as both a principal site for nanoparticle distribution and a significant reservoir of putative EPCs. The in situ reprogramming of splenic EPCs offers a potential solution to overcome critical challenges, including the aforementioned insufficient dosage and complex ex vivo processing.

Key Messages

This review explores the latest advancements in EPC therapy and in situ reprogramming, spotlighting a pioneering study that integrates those two strategies with a specific focus on the spleen. Such an innovative approach will potentially herald a new era of regenerative therapy for ischemic heart disease.

Programming human cell fate: overcoming challenges and unlocking potential through technological breakthroughs

In recent years, there have been notable advancements in the ability to programme human cell identity, enabling us to design and manipulate cell function in a Petri dish. However, current protocols for generating target cell types often lack efficiency and precision, resulting in engineered cells that do not fully replicate the desired identity or functional output. This applies to different methods of cell programming, which face similar challenges that hinder progress and delay the achievement of a more favourable outcome. However, recent technological and analytical breakthroughs have provided us with unprecedented opportunities to advance the way we programme cell fate. The Company of Biologists' 2023 workshop on 'Novel Technologies for Programming Human Cell Fate' brought together experts in human cell fate engineering and experts in single-cell genomics, manipulation and characterisation of cells on a single (sub)cellular level. Here, we summarise the main points that emerged during the workshop's themed discussions. Furthermore, we provide specific examples highlighting the current state of the field as well as its trajectory, offering insights into the potential outcomes resulting from the application of these breakthrough technologies in precisely engineering the identity and function of clinically valuable human cells.

Challenges of CRISPR/Cas-Based Cell Therapy for Type 1 Diabetes: How Not to Engineer a "Trojan Horse"

Type 1 diabetes mellitus (T1D) is an autoimmune disease caused by the destruction of insulin-producing β-cells in the pancreas by cytotoxic T-cells. To date, there are no drugs that can prevent the development of T1D. Insulin replacement therapy is the standard care for patients with T1D. This treatment is life-saving, but is expensive, can lead to acute and long-term complications, and results in reduced overall life expectancy. This has stimulated the research and development of alternative treatments for T1D. In this review, we consider potential therapies for T1D using cellular regenerative medicine approaches with a focus on CRISPR/Cas-engineered cellular products. However, CRISPR/Cas as a genome editing tool has several drawbacks that should be considered for safe and efficient cell engineering. In addition, cellular engineering approaches themselves pose a hidden threat. The purpose of this review is to critically discuss novel strategies for the treatment of T1D using genome editing technology. A well-designed approach to β-cell derivation using CRISPR/Cas-based genome editing technology will significantly reduce the risk of incorrectly engineered cell products that could behave as a "Trojan horse".

Dynamic scRNA-seq of live human pancreatic slices reveals functional endocrine cell neogenesis through an intermediate ducto-acinar stage

Human pancreatic plasticity is implied from multiple single-cell RNA sequencing (scRNA-seq) studies. However, these have been invariably based on static datasets from which fate trajectories can only be inferred using pseudotemporal estimations. Furthermore, the analysis of isolated islets has resulted in a drastic underrepresentation of other cell types, hindering our ability to interrogate exocrine-endocrine interactions. The long-term culture of human pancreatic slices (HPSs) has presented the field with an opportunity to dynamically track tissue plasticity at the single-cell level. Combining datasets from same-donor HPSs at different time points, with or without a known regenerative stimulus (BMP signaling), led to integrated single-cell datasets storing true temporal or treatment-dependent information. This integration revealed population shifts consistent with ductal progenitor activation, blurring of ductal/acinar boundaries, formation of ducto-acinar-endocrine differentiation axes, and detection of transitional insulin-producing cells. This study provides the first longitudinal scRNA-seq analysis of whole human pancreatic tissue, confirming its plasticity in a dynamic fashion.

Reprogramming of pancreatic islet cells for regeneration and rejuvenation

The pancreatic β cell, which produces insulin, is a terminally differentiated cell type that divides rarely. Consequently, the regenerative ability of β cells is limited and irreversible diabetes occurs after severe loss of β-cell function. In view of such poor regenerative capacity, considerable research efforts have been made to promote the expansion of functional insulin-producing cells as a regenerative therapy for diabetes. Here, we discuss recent findings regarding the robust expansion of functional mature islet cells both in vivo and ex vivo through MYCL-mediated reprogramming. We also describe the potential prospects for the application of reprogramming technologies to regenerative therapy and rejuvenation of islet cells.

Single-cell epigenome analysis identifies molecular events controlling direct conversion of human fibroblasts to pancreatic ductal-like cells

Cell fate can be reprogrammed by ectopic expression of lineage-specific transcription factors (TFs). However, the exact cell state transitions during transdifferentiation are still poorly understood. Here, we have generated pancreatic exocrine cells of ductal epithelial identity from human fibroblasts using a set of six TFs. We mapped the molecular determinants of lineage dynamics using a factor-indexing method based on single-nuclei multiome sequencing (FI-snMultiome-seq) that enables dissecting the role of each individual TF and pool of TFs in cell fate conversion. We show that transition from mesenchymal fibroblast identity to epithelial pancreatic exocrine fate involves two deterministic steps: an endodermal progenitor state defined by activation of HHEX with FOXA2 and SOX17 and a temporal GATA4 activation essential for the maintenance of pancreatic cell fate program. Collectively, our data suggest that transdifferentiation-although being considered a direct cell fate conversion method-occurs through transient progenitor states orchestrated by stepwise activation of distinct TFs.

Engineering natural molecule-triggered genetic control systems for tunable gene- and cell-based therapies

The ability to precisely control activities of engineered designer cells provides a novel strategy for modern precision medicine. Dynamically adjustable gene- and cell-based precision therapies are recognized as next generation medicines. However, the translation of these controllable therapeutics into clinical practice is severely hampered by the lack of safe and highly specific genetic switches controlled by triggers that are nontoxic and side-effect free. Recently, natural products derived from plants have been extensively explored as trigger molecules to control genetic switches and synthetic gene networks for multiple applications. These controlled genetic switches could be further introduced into mammalian cells to obtain synthetic designer cells for adjustable and fine tunable cell-based precision therapy. In this review, we introduce various available natural molecules that were engineered to control genetic switches for controllable transgene expression, complex logic computation, and therapeutic drug delivery to achieve precision therapy. We also discuss current challenges and prospects in translating these natural molecule-controlled genetic switches developed for biomedical applications from the laboratory to the clinic.

Inferring regulators of cell identity in the human adult pancreas

Cellular identity during development is under the control of transcription factors that form gene regulatory networks. However, the transcription factors and gene regulatory networks underlying cellular identity in the human adult pancreas remain largely unexplored. Here, we integrate multiple single-cell RNA-sequencing datasets of the human adult pancreas, totaling 7393 cells, and comprehensively reconstruct gene regulatory networks. We show that a network of 142 transcription factors forms distinct regulatory modules that characterize pancreatic cell types. We present evidence that our approach identifies regulators of cell identity and cell states in the human adult pancreas. We predict that HEYL, BHLHE41 and JUND are active in acinar, beta and alpha cells, respectively, and show that these proteins are present in the human adult pancreas as well as in human induced pluripotent stem cell (hiPSC)-derived islet cells. Using single-cell transcriptomics, we found that JUND represses beta cell genes in hiPSC-alpha cells. BHLHE41 depletion induced apoptosis in primary pancreatic islets. The comprehensive gene regulatory network atlas can be explored interactively online. We anticipate our analysis to be the starting point for a more sophisticated dissection of how transcription factors regulate cell identity and cell states in the human adult pancreas.

Unlocking the post-transplant microenvironment for successful islet function and survival

Islet transplantation (IT) offers the potential to restore euglycemia for patients with type 1 diabetes mellitus (T1DM). Despite improvements in islet isolation techniques and immunosuppressive regimes, outcomes remain suboptimal with UK five-year graft survivals (5YGS) of 55% and most patients still requiring exogenous insulin after multiple islet infusions. Native islets have a significant non-endocrine component with dense extra-cellular matrix (ECM), important for islet development, cell survival and function. Collagenase isolation necessarily disrupts this complex islet microenvironment, leaving islets devoid of a supporting framework and increasing vulnerability of transplanted islets. Following portal venous transplantation, a liver injury response is potentially induced, which typically results in inflammation and ECM deposition from liver specific myofibroblasts. The impact of this response may have important impact on islet survival and function. A fibroblast response and ECM deposition at the kidney capsule and eye chamber alongside other implantation sites have been shown to be beneficial for survival and function. Investigating the implantation site microenvironment and the interactions of transplanted islets with ECM proteins may reveal therapeutic interventions to improve IT and stem-cell derived beta-cell therapy.

Engineered neurogenesis in naïve adult rat cortex by Ngn2-mediated neuronal reprogramming of resident oligodendrocyte progenitor cells

Adult tissue stem cells contribute to tissue homeostasis and repair but the long-lived neurons in the human adult cerebral cortex are not replaced, despite evidence for a limited regenerative response. However, the adult cortex contains a population of proliferating oligodendrocyte progenitor cells (OPCs). We examined the capacity of rat cortical OPCs to be re-specified to a neuronal lineage both in vitro and in vivo. Expressing the developmental transcription factor Neurogenin2 (Ngn2) in OPCs isolated from adult rat cortex resulted in their expression of early neuronal lineage markers and genes while downregulating expression of OPC markers and genes. Ngn2 induced progression through a neuronal lineage to express mature neuronal markers and functional activity as glutamatergic neurons. In vivo retroviral gene delivery of Ngn2 to naive adult rat cortex ensured restricted targeting to proliferating OPCs. Ngn2 expression in OPCs resulted in their lineage re-specification and transition through an immature neuronal morphology into mature pyramidal cortical neurons with spiny dendrites, axons, synaptic contacts, and subtype specification matching local cytoarchitecture. Lineage re-specification of rat cortical OPCs occurred without prior injury, demonstrating these glial progenitor cells need not be put into a reactive state to achieve lineage reprogramming. These results show it may be feasible to precisely engineer additional neurons directly in adult cerebral cortex for experimental study or potentially for therapeutic use to modify dysfunctional or damaged circuitry.

Cell Transdifferentiation: A Challenging Strategy with Great Potential

With the discovery and development of somatic cell nuclear transfer, cell fusion, and induced pluripotent stem cells, cell transdifferentiation research has presented unique advantages and stimulated a heated discussion worldwide. Cell transdifferentiation is a phenomenon by which a cell changes its lineage and acquires the phenotype of other cell types when exposed to certain conditions. Indeed, many adult stem cells and differentiated cells were reported to change their phenotype and transform into other lineages. This article reviews the differentiation of stem cells and classification of transdifferentiation, as well as the advantages, challenges, and prospects of cell transdifferentiation. This review discusses new research directions and the main challenges in the use of transdifferentiation in human cells and molecular replacement therapy. Overall, such knowledge is expected to provide a deep understanding of cell fate and regulation, which can change through differentiation, dedifferentiation, and transdifferentiation, with multiple applications.

Reversing pancreatic β-cell dedifferentiation in the treatment of type 2 diabetes

The maintenance of glucose homeostasis is fundamental for survival and health. Diabetes develops when glucose homeostasis fails. Type 2 diabetes (T2D) is characterized by insulin resistance and pancreatic β-cell failure. The failure of β-cells to compensate for insulin resistance results in hyperglycemia, which in turn drives altered lipid metabolism and β-cell failure. Thus, insulin secretion by pancreatic β-cells is a primary component of glucose homeostasis. Impaired β-cell function and reduced β-cell mass are found in diabetes. Both features stem from a failure to maintain β-cell identity, which causes β-cells to dedifferentiate into nonfunctional endocrine progenitor-like cells or to trans-differentiate into other endocrine cell types. In this regard, one of the key issues in achieving disease modification is how to reestablish β-cell identity. In this review, we focus on the causes and implications of β-cell failure, as well as its potential reversibility as a T2D treatment.

Endothelial cell direct reprogramming: Past, present, and future

Ischemic cardiovascular disease still remains as a leading cause of morbidity and mortality despite various medical, surgical, and interventional therapy. As such, cell therapy has emerged as an attractive option because it tackles underlying problem of the diseases by inducing neovascularization in ischemic tissue. After overall failure of adult stem or progenitor cells, studies attempted to generate endothelial cells (ECs) from pluripotent stem cells (PSCs). While endothelial cells (ECs) differentiated from PSCs successfully induced vascular regeneration, differentiating volatility and tumorigenic potential is a concern for their clinical applications. Alternatively, direct reprogramming strategies employ lineage-specific factors to change cell fate without achieving pluripotency. ECs have been successfully reprogrammed via ectopic expression of transcription factors (TFs) from endothelial lineage. The reprogrammed ECs induced neovascularization in vitro and in vivo and thus demonstrated their therapeutic value in animal models of vascular insufficiency. Methods of delivering reprogramming factors include lentiviral or retroviral vectors and more clinically relevant, non-integrative adenoviral and episomal vectors. Most studies made use of fibroblast as a source cell for reprogramming, but reprogrammability of other clinically relevant source cell types has to be evaluated. Specific mechanisms and small molecules that are involved in the aforementioned processes tackles challenges associated with direct reprogramming efficiency and maintenance of reprogrammed EC characteristics. After all, this review provides summary of past and contemporary methods of direct endothelial reprogramming and discusses the future direction to overcome these challenges to acquire clinically applicable reprogrammed ECs.

Pharmacological inhibition of human EZH2 can influence a regenerative β-like cell capacity with in vitro insulin release in pancreatic ductal cells

BACKGROUND

Therapeutic replacement of pancreatic endocrine β-cells is key to improving hyperglycaemia caused by insulin-dependent diabetes . Whilst the pool of ductal progenitors, which give rise to the endocrine cells, are active during development, neogenesis of islets is repressed in the human adult. Recent human donor studies have demonstrated the role of EZH2 inhibition in surgically isolated exocrine cells showing reactivation of insulin expression and the influence on the H3K27me3 barrier to β-cell regeneration. However, those studies fall short on defining the cell type active in transcriptional reactivation events. This study examines the role of the regenerative capacity of human pancreatic ductal cells when stimulated with pharmacological inhibitors of the EZH2 methyltransferase.

RESULTS

Human pancreatic ductal epithelial cells were stimulated with the EZH2 inhibitors GSK-126, EPZ6438, and triptolide using a 2- and 7-day protocol to determine their influence on the expression of core endocrine development marker NGN3, as well as β-cell markers insulin, MAFA, and PDX1. Chromatin immunoprecipitation studies show a close correspondence of pharmacological EZH2 inhibition with reduced H3K27me3 content of the core genes, NGN3, MAFA and PDX1. Consistent with the reduction of H3K27me3 by pharmacological inhibition of EZH2, we observe measurable immunofluorescence staining of insulin protein and glucose-sensitive insulin response.

CONCLUSION

The results of this study serve as a proof of concept for a probable source of β-cell induction from pancreatic ductal cells that are capable of influencing insulin expression. Whilst pharmacological inhibition of EZH2 can stimulate secretion of detectable insulin from ductal progenitor cells, further studies are required to address mechanism and the identity of ductal progenitor cell targets to improve likely methods designed to reduce the burden of insulin-dependent diabetes.

Transcriptomic Characterization of Genes Regulating the Stemness in Porcine Atrial Cardiomyocytes during Primary In Vitro Culture

Heart failure remains a major cause of death worldwide. There is a need to establish new management options as current treatment is frequently suboptimal. Clinical approaches based on autologous stem cell transplant is potentially a good alternative. The heart was long considered an organ unable to regenerate and renew. However, several reports imply that it may possess modest intrinsic regenerative potential. To allow for detailed characterization of cell cultures, whole transcriptome profiling was performed after 0, 7, 15, and 30 days of in vitro cell cultures (IVC) from the right atrial appendage and right atrial wall utilizing microarray technology. In total, 4239 differentially expressed genes (DEGs) with ratio > abs |2| and adjusted p-value ≤ 0.05 for the right atrial wall and 4662 DEGs for the right atrial appendage were identified. It was shown that a subset of DEGs, which have demonstrated some regulation of expression levels with the duration of the cell culture, were enriched in the following GO BP (Gene Ontology Biological Process) terms: "stem cell population maintenance" and "stem cell proliferation". The results were validated by RT-qPCR. The establishment and detailed characterization of in vitro culture of myocardial cells may be important for future applications of these cells in heart regeneration processes.

Transcription factors and splice factors - interconnected regulators of stem cell differentiation

Purpose of review

The underlying molecular mechanisms that direct stem cell differentiation into fully functional, mature cells remain an area of ongoing investigation. Cell state is the product of the combinatorial effect of individual factors operating within a coordinated regulatory network. Here, we discuss the contribution of both gene regulatory and splicing regulatory networks in defining stem cell fate during differentiation and the critical role of protein isoforms in this process.

Recent findings

We review recent experimental and computational approaches that characterize gene regulatory networks, splice regulatory networks, and the resulting transcriptome and proteome they mediate during differentiation. Such approaches include long-read RNA sequencing, which has demonstrated high-resolution profiling of mRNA isoforms, and Cas13-based CRISPR, which could make possible high-throughput isoform screening. Collectively, these developments enable systems-level profiling of factors contributing to cell state.

Summary

Overall, gene and splice regulatory networks are important in defining cell state. The emerging high-throughput systems-level approaches will characterize the gene regulatory network components necessary in driving stem cell differentiation.