Transgenic mice with green fluorescent protein-labeled pancreatic beta -cells

The anterior chamber of the eye technology and its anatomical, optical, and immunological bases

The anterior chamber of the eye (ACE) is distinct in its anatomy, optics, and immunology. This guarantees that the eye perceives visual information in the context of physiology even when encountering adverse incidents like inflammation. In addition, this endows the ACE with the special nursery bed iris enriched in vasculatures and nerves. The ACE constitutes a confined space enclosing an oxygen/nutrient-rich, immune-privileged, and less stressful milieu as well as an optically transparent medium. Therefore, aside from visual perception, the ACE unexpectedly serves as an excellent transplantation site for different body parts and a unique platform for noninvasive, longitudinal, and intravital microimaging of different grafts. On the basis of these merits, the ACE technology has evolved from the prototypical through the conventional to the advanced version. Studies using this technology as a versatile biomedical research platform have led to a diverse range of basic knowledge and in-depth understanding of a variety of cells, tissues, and organs as well as artificial biomaterials, pharmaceuticals, and abiotic substances. Remarkably, the technology turns in vivo dynamic imaging of the morphological characteristics, organotypic features, developmental fates, and specific functions of intracameral grafts into reality under physiological and pathological conditions. Here we review the anatomical, optical, and immunological bases as well as technical details of the ACE technology. Moreover, we discuss major achievements obtained and potential prospective avenues for this technology.

Local Dialogues Between the Endocrine and Exocrine Cells in the Pancreas

For many years, it has been taught in medical textbooks that the endocrine and exocrine parts of the pancreas have separate blood supplies that do not mix. Therefore, they have been studied by different scientific communities, and patients with pancreatic disorders are treated by physicians in different medical disciplines, where endocrine and exocrine function are the focus of endocrinologists and gastroenterologists, respectively. The conventional model that every islet in each pancreatic lobule receives a dedicated arterial blood supply was first proposed in 1932, and it has been inherited to date. Recently, in vivo intravital recording of red blood cell flow in mouse islets as well as in situ structural analysis of 3D pancreatic vasculature from hundreds of islets provided evidence for preferentially integrated pancreatic blood flow in six mammalian species. The majority of islets have no association with the arteriole, and there is bidirectional blood exchange between the two segments. Such vascularization may allow an entire downstream region of islets and acinar cells to be simultaneously exposed to a topologically and temporally specific plasma content, which could underlie an adaptive sensory function as well as common pathogeneses of both portions of the organ in pancreatic diseases, including diabetes.

ARTICLE HIGHLIGHTS

The adhesion GPCR GPR116/ADGRF5 has a dual function in pancreatic islets regulating somatostatin release and islet development

Glucose homeostasis is maintained by hormones secreted from different cell types of the pancreatic islets and controlled by manifold input including signals mediated through G protein-coupled receptors (GPCRs). RNA-seq analyses revealed expression of numerous GPCRs in mouse and human pancreatic islets, among them Gpr116/Adgrf5. GPR116 is an adhesion GPCR mainly found in lung and required for surfactant secretion. Here, we demonstrate that GPR116 is involved in the somatostatin release from pancreatic delta cells using a whole-body as well as a cell-specific knock-out mouse model. Interestingly, the whole-body GPR116 deficiency causes further changes such as decreased beta-cell mass, lower number of small islets, and reduced pancreatic insulin content. Glucose homeostasis in global GPR116-deficient mice is maintained by counter-acting mechanisms modulating insulin degradation. Our data highlight an important function of GPR116 in controlling glucose homeostasis.

Phagocytosis by macrophages promotes pancreatic β cell mass reduction after parturition in mice

Elucidating the mechanism(s) modulating appropriate tissue size is a critical biological issue. Pancreatic β cells increase during pregnancy via cellular proliferation, but how β cells promptly decrease to the original amount after parturition remains unclear. Herein, we demonstrate the role and mechanism of macrophage accumulation in this process. In the final stage of pregnancy, HTR1D signaling upregulates murine β cell CXCL10, thereby promoting macrophage accumulation in pancreatic islets via the CXCL10-CXCR3 axis. Blocking this mechanism by administering an HTR1D antagonist or the CXCR3 antibody and depleting islet macrophages inhibited postpartum β cell mass reduction. β cells engulfed by macrophages increased in postpartum islets, but Annexin V administration suppressed this engulfment and the postpartum β cell mass reduction, indicating the accumulated macrophages to phagocytose β cells. This mechanism contributes to both maintenance of appropriate β cell mass and glucose homeostasis promptly adapting to reduced systemic insulin demand after parturition.

Engineered extracellular vesicles from human skin cells induce pro-β-cell conversions in pancreatic ductal cells

Direct nuclear reprogramming has the potential to enable the development of β cell replacement therapies for diabetes that do not require the use of progenitor/stem cell populations. However, despite their promise, current approaches to β cell-directed reprogramming rely heavily on the use of viral vectors. Here we explored the use of extracellular vesicles (EVs) derived from human dermal fibroblasts (HDFs) as novel non-viral carriers of endocrine cell-patterning transcription factors, to transfect and transdifferentiate pancreatic ductal epithelial cells (PDCs) into hormone-expressing cells. Electrotransfection of HDFs with expression plasmids for Pdx1, Ngn3, and MafA (PNM) led to the release of EVs loaded with PNM at the gene, mRNA, and protein level. Exposing PDC cultures to PNM-loaded EVs led to successful transfection and increased PNM expression in PDCs, which ultimately resulted in endocrine cell-directed conversions based on the expression of insulin/c-peptide, glucagon, and glucose transporter 2 (Glut2). These findings were further corroborated in vivo in a mouse model following intraductal injection of PNM- vs sham-loaded EVs. Collectively these findings suggest that dermal fibroblast-derived EVs could potentially serve as a powerful platform technology for the development and deployment of non-viral reprogramming-based cell therapies for insulin-dependent diabetes.

DNA Methylation-Dependent Restriction of Tyrosine Hydroxylase Contributes to Pancreatic β-Cell Heterogeneity

The molecular and functional heterogeneity of pancreatic β-cells is well recognized, but the underlying mechanisms remain unclear. Pancreatic islets harbor a subset of β-cells that co-express tyrosine hydroxylase (TH), an enzyme involved in synthesis of catecholamines that repress insulin secretion. Restriction of the TH+ β-cells within islets is essential for appropriate function in mice, such that a higher proportion of these cells corresponds to reduced insulin secretion. Here, we use these cells as a model to dissect the developmental control of β-cell heterogeneity. We define the specific molecular and metabolic characteristics of TH+ β-cells and show differences in their developmental restriction in mice and humans. We show that TH expression in β-cells is restricted by DNA methylation during β-cell differentiation. Ablation of de novo DNA methyltransferase Dnmt3a in the embryonic progenitors results in a dramatic increase in the proportion of TH+ β-cells, whereas β-cell-specific ablation of Dnmt3a does not. We demonstrate that maintenance of Th promoter methylation is essential for its continued restriction in postnatal β-cells. Loss of Th promoter methylation in response to chronic overnutrition increases the number of TH+ β-cells, corresponding to impaired β-cell function. These results reveal a regulatory role of DNA methylation in determining β-cell heterogeneity.

Pancreatic islet cell type-specific transcriptomic changes during pregnancy and postpartum

Pancreatic β-cell mass expands during pregnancy and regresses in the postpartum period in conjunction with dynamic metabolic demands on maternal glucose homeostasis. To understand transcriptional changes driving these adaptations in β-cells and other islet cell types, we performed single-cell RNA sequencing on islets from virgin, late gestation, and early postpartum mice. We identified transcriptional signatures unique to gestation and the postpartum in β-cells, including induction of the AP-1 transcription factor subunits and other genes involved in the immediate-early response (IEGs). In addition, we found pregnancy and postpartum-induced changes differed within each endocrine cell type, and in endothelial cells and antigen-presenting cells within islets. Together, our data reveal insights into cell type-specific transcriptional changes responsible for adaptations by islet cells to pregnancy and their resolution postpartum.

Localized cytotoxic T cell-associated antigen 4 and antioxidant islet encapsulation alters macrophage signaling and induces regulatory and anergic T cells to enhance allograft survival

The loss of functional β-cell mass is a hallmark of type 1 diabetes. Islet transplantation represents a promising alternative approach, but immune-mediated graft destruction remains a major challenge. We sought to use islet encapsulation technologies to improve graft survival and function without systemic immunosuppression. We hypothesized islet encapsulation with nanothin coatings consisting of tannic acid (TA), an antioxidant; poly(N-vinylpyrrolidone) (PVPON), a biocompatible polymer; and cytotoxic T cell-associated antigen 4 immunoglobulin (CTLA-4-Ig), an inhibitory immune receptor, will elicit localized immunosuppression to prolong islet allograft function and suppress effector T cell responses. In the absence of systemic immunosuppression, we demonstrated (PVPON/TA/CTLA-4-Ig)-encapsulated NOD.Rag islet grafts maintain function significantly longer than control IgG-containing (PVPON/TA/IgG) and nonencapsulated controls after transplantation into diabetic C57BL/6 mice. This protection coincided with diminished proinflammatory macrophage responses mediated by signal transducer and activator of transcription 1 signaling, decreased proinflammatory T cell effector responses, and CTLA-4-Ig-specific concomitant increases in anergic CD4+ T cells and regulatory T cells. Our results provide evidence that conjugation of CTLA-4-Ig to (PVPON/TA) coatings can suppress T cell activation, enhance regulatory T cell populations, prolong islet allograft survival, and induce localized immunosuppression after transplantation.

Cell-Surface Autoantibody Targets Zinc Transporter-8 (ZnT8) for In Vivo β-Cell Imaging and Islet-Specific Therapies

Type 1 diabetes (T1D) is a disease in which autoimmune attacks are directed at the insulin-producing β-cell in the pancreatic islet. Autoantigens on the β-cell surface membrane are specific markers for molecular recognition and targets for engagement by autoreactive B lymphocytes, which produce islet cell surface autoantibody (ICSA) upon activation. We report the cloning of an ICSA (mAb43) that recognizes a major T1D autoantigen, ZnT8, with a subnanomolar binding affinity and conformation specificity. We demonstrate that cell-surface binding of mAb43 protects the extracellular epitope of ZnT8 against immunolabeling by serum ICSA from a patient with T1D. Furthermore, mAb43 exhibits in vitro and ex vivo specificity for islet cells, mirroring the exquisite specificity of islet autoimmunity in T1D. Systemic administration of mAb43 yields a pancreas-specific biodistribution in mice and islet homing of an mAb43-linked imaging payload through the pancreatic vasculature, thereby validating the in vivo specificity of mAb43. Identifying ZnT8 as a major antigenic target of ICSA allows for research into the molecular recognition and engagement of autoreactive B cells in the chronic phase of T1D progression. The in vivo islet specificity of mAb43 could be further exploited to develop in vivo imaging and islet-specific immunotherapies.

Reduced calcium levels and accumulation of abnormal insulin granules in stem cell models of HNF1A deficiency

Mutations in HNF1A cause Maturity Onset Diabetes of the Young (HNF1A-MODY). To understand mechanisms of β-cell dysfunction, we generated stem cell-derived pancreatic endocrine cells with hypomorphic mutations in HNF1A. HNF1A-deficient β-cells display impaired basal and glucose stimulated-insulin secretion, reduced intracellular calcium levels in association with a reduction in CACNA1A expression, and accumulation of abnormal insulin granules in association with SYT13 down-regulation. Knockout of CACNA1A and SYT13 reproduce the relevant phenotypes. In HNF1A deficient β-cells, glibenclamide, a sulfonylurea drug used in the treatment of HNF1A-MODY patients, increases intracellular calcium, and restores insulin secretion. While insulin secretion defects are constitutive in β-cells null for HNF1A, β-cells heterozygous for hypomorphic HNF1A (R200Q) mutations lose the ability to secrete insulin gradually; this phenotype is prevented by correction of the mutation. Our studies illuminate the molecular basis for the efficacy of treatment of HNF1A-MODY with sulfonylureas, and suggest promise for the use of cell therapies.

Transgenic overexpression of microRNA-30d in pancreatic beta-cells progressively regulates beta-cell function and identity

Abnormal microRNA functions are closely associated with pancreatic β-cell loss and dysfunction in type 2 diabetes. Dysregulation of miR-30d has been reported in the individuals with diabetes. To study how miR-30d affects pancreatic β-cell functions, we generated two transgenic mouse lines that specifically overexpressed miR-30d in β-cells at distinct low and high levels. Transgenic overexpressed miR-30d systemically affected β-cell function. Elevated miR-30d at low-level (TgL, 2-fold) had mild effects on signaling pathways and displayed no significant changes to metabolic homeostasis. In contrast, transgenic mice with high-level of miR-30d expression (TgH, 12-fold) exhibited significant diet-induced hyperglycemia and β-cell dysfunction. In addition, loss of β-cell identity was invariably accompanied with increased insulin/glucagon-double positive bihormonal cells and excess plasma glucagon levels. The transcriptomic analysis revealed that miR-30d overexpression inhibited β-cell-enriched gene expression and induced α-cell-enriched gene expression. These findings implicate that an appropriate miR-30d level is essential in maintaining normal β-cell identity and function.

Type 2 Diabetes Mellitus: Pathogenic Features and Experimental Models in Rodents

Type 2 diabetes mellitus (T2DM) is the most common endocrine disorder (90%) in the world; it has numerous clinical, immunological, and genetic differences from type 1 diabetes mellitus. The pathogenesis of T2DM is complex and not fully clear. To date, animal models remain the main tool by which to study the pathophysiology and therapy of T2DM. Rodents are considered the best choice among animal models, because they are characterized by a small size, short induction period, easy diabetes induction, and economic efficiency. This review summarizes data on experimental models of T2DM that are currently used, evaluates their advantages and disadvantages vis-a-vis research, and describes in detail the factors that should be taken into account when using these models. Selection of a suitable model for tackling a particular issue is not always trivial; it affects study results and their interpretation.

Enhanced characterization of beta cell mass in a Tg(Pdx1-GFP) mouse model

Introduction: Measurement of pancreatic beta cell mass in animal models is a common assay in diabetes researches. Novel whole-organ clearance methods in conjunction with transgenic mouse models hold tremendous promise to improve beta cell mass measurement methods. Here, we proposed a refined method to estimate the beta cell mass using a new transgenic Tg(Pdx1-GFP) mouse model and a recently developed free-of-acrylamide clearing tissue (FACT) protocol. Methods: First, we generated and evaluated a Tg(Pdx1-GFP) transgenic mouse model. Using the FACT protocol in our model, we could quantify the beta cell mass and alloxan-induced beta cell destruction in whole pancreas specimens. Results: Compiled fluorescent images of pancreas resulted in enhanced beta cell mass characterization in FACT-cleared sections (2928869±120215 AU) compared to No-FACT cleared sections (1292372±325632 AU). Additionally, the total number of detected islets with this method was significantly higher than the other clearance methods (155.7 and 109, respectively). Using this method, we showed green fluorescent protein (GFP) expression confined to beta cells in Tg(Pdx1-GFP) transgenic. This enhanced GFP expression enabled us to accurately measure beta cell loss in a beta cell destruction model. The results suggest that our proposed method can be used as a simple, and rapid assay for beta cell mass measurement in islet biology and diabetes studies. Conclusion: The Tg(Pdx1-GFP) transgenic mouse in conjunction with the FACT protocol can enhance large-scale screening studies in the field of diabetes.

Spatial and transcriptional heterogeneity of pancreatic beta cell neogenesis revealed by a time-resolved reporter system

AIMS/HYPOTHESIS

While pancreatic beta cells have been shown to originate from endocrine progenitors in ductal regions, it remains unclear precisely where beta cells emerge from and which transcripts define newborn beta cells. We therefore investigated characteristics of newborn beta cells extracted by a time-resolved reporter system.

METHODS

We established a mouse model, 'Ins1-GFP; Timer', which provides spatial information during beta cell neogenesis with high temporal resolution. Single-cell RNA-sequencing (scRNA-seq) was performed on mouse beta cells sorted by fluorescent reporter to uncover transcriptomic profiles of newborn beta cells. scRNA-seq of human embryonic stem cell (hESC)-derived beta-like cells was also performed to compare newborn beta cell features between mouse and human.

RESULTS

Fluorescence imaging of Ins1-GFP; Timer mouse pancreas successfully dissected newly generated beta cells as green fluorescence-dominant cells. This reporter system revealed that, as expected, some newborn beta cells arise close to the ducts (β^duct); unexpectedly, the others arise away from the ducts and adjacent to blood vessels (β^vessel). Single-cell transcriptomic analyses demonstrated five distinct populations among newborn beta cells, confirming spatial heterogeneity of beta cell neogenesis such as high probability of glucagon-positive β^duct, musculoaponeurotic fibrosarcoma oncogene family B (MafB)-positive β^duct and musculoaponeurotic fibrosarcoma oncogene family A (MafA)-positive β^vessel cells. Comparative analysis with scRNA-seq data of mouse newborn beta cells and hESC-derived beta-like cells uncovered transcriptional similarity between mouse and human beta cell neogenesis including microsomal glutathione S-transferase 1 (MGST1)- and synaptotagmin 13 (SYT13)-highly-expressing state.

CONCLUSIONS/INTERPRETATION

The combination of time-resolved histological imaging with single-cell transcriptional mapping demonstrated novel features of spatial and transcriptional heterogeneity in beta cell neogenesis, which will lead to a better understanding of beta cell differentiation for future cell therapy.

DATA AVAILABILITY

Raw and processed single-cell RNA-sequencing data for this study has been deposited in the Gene Expression Omnibus under accession number GSE155742.

Cell Networks in Endocrine/Neuroendocrine Gland Function

Reproduction, growth, stress, and metabolism are determined by endocrine/neuroendocrine systems that regulate circulating hormone concentrations. All these systems generate rhythms and changes in hormone pulsatility observed in a variety of pathophysiological states. Thus, the output of endocrine/neuroendocrine systems must be regulated within a narrow window of effective hormone concentrations but must also maintain a capacity for plasticity to respond to changing physiological demands. Remarkably most endocrinologists still have a "textbook" view of endocrine gland organization which has emanated from 20^th century histological studies on thin 2D tissue sections. However, 21^st -century technological advances, including in-depth 3D imaging of specific cell types have vastly changed our knowledge. We now know that various levels of multicellular organization can be found across different glands, that organizational motifs can vary between species and can be modified to enhance or decrease hormonal release. This article focuses on how the organization of cells regulates hormone output using three endocrine/neuroendocrine glands that present different levels of organization and complexity: the adrenal medulla, with a single neuroendocrine cell type; the anterior pituitary, with multiple intermingled cell types; and the pancreas with multiple intermingled cell types organized into distinct functional units. We give an overview of recent methodologies that allow the study of the different components within endocrine systems, particularly their temporal and spatial relationships. We believe the emerging findings about network organization, and its impact on hormone secretion, are crucial to understanding how homeostatic regulation of endocrine axes is carried out within endocrine organs themselves. © 2022 American Physiological Society. Compr Physiol 12:3371-3415, 2022.

Role of angiogenesis in beta-cell epithelial-mesenchymal transition in chronic pancreatitis-induced diabetes

Clinical evidence suggests that patients with chronic pancreatitis (CP) are prone to development of diabetes (chronic pancreatitis-related diabetes; CPRD), whereas the underlying mechanisms are not fully determined. Recently, we showed that the gradual loss of functional beta-cells in a mouse model for CPRD, partial pancreatic duct ligation (PDL), results from a transforming growth factor β1 (TGFβ1)-triggered beta-cell epithelial-mesenchymal transition (EMT), rather than from apoptotic beta-cell death. Here, the role of angiogenesis in CPRD-associated beta-cell EMT was addressed. We detected enhanced angiogenesis in the inflamed pancreas from CP patients by bioinformatic analysis and from PDL-mice. Inhibition of angiogenesis by specific antisera for vascular endothelial growth factor receptor 2 (VEGFR2), DC101, did not alter the loss of beta-cells and the fibrotic process in PDL-pancreas. However, DC101-mediated inhibition of angiogenesis abolished pancreatitis-induced beta-cell EMT and rendered it to apoptotic beta-cell death. Thus, our data suggest that angiogenesis promotes beta-cell survival in the inflamed pancreas, while suppression of angiogenesis turns beta-cell EMT into apoptotic beta-cell death. This finding could be informative during development of intervention therapies for CPRD.

A Pro-Endocrine Pancreatic Islet Transcriptional Program Established During Development Is Retained in Human Gallbladder Epithelial Cells

BACKGROUND & AIMS

Pancreatic islet β-cells are factories for insulin production; however, ectopic expression of insulin also is well recognized. The gallbladder is a next-door neighbor to the developing pancreas. Here, we wanted to understand if gallbladders contain functional insulin-producing cells.

METHODS

We compared developing and adult mouse as well as human gallbladder epithelial cells and islets using immunohistochemistry, flow cytometry, enzyme-linked immunosorbent assays, RNA sequencing, real-time polymerase chain reaction, chromatin immunoprecipitation, and functional studies.

RESULTS

We show that the epithelial lining of developing, as well as adult, mouse and human gallbladders naturally contain interspersed cells that retain the capacity to actively transcribe, translate, package, and release insulin. We show that human gallbladders also contain functional insulin-secreting cells with the potential to naturally respond to glucose in vitro and in situ. Notably, in a non-obese diabetic (NOD) mouse model of type 1 diabetes, we observed that insulin-producing cells in the gallbladder are not targeted by autoimmune cells. Interestingly, in human gallbladders, insulin splice variants are absent, although insulin splice forms are observed in human islets.

CONCLUSIONS

In summary, our biochemical, transcriptomic, and functional data in mouse and human gallbladder epithelial cells collectively show the evolutionary and developmental similarities between gallbladder and the pancreas that allow gallbladder epithelial cells to continue insulin production in adult life. Understanding the mechanisms regulating insulin transcription and translation in gallbladder epithelial cells would help guide future studies in type 1 diabetes therapy.

Development of novel radioiodinated exendin-4 derivatives targeting GLP-1 receptor for detection of β-cell mass

In subjects with type 2 diabetes mellitus (T2DM), pancreatic β-cell mass decreases; however, it is unknown to what extent this decrease contributes to the pathophysiology of T2DM. Therefore, the development of a method for noninvasive detection of β-cell mass is underway. We previously reported that glucagon-like peptide-1 receptor (GLP-1R) is a promising target molecule for β-cell imaging. In this study, we attempted to develop a probe targeting GLP-1R for β-cell imaging using single-photon emission computed tomography (SPECT). For this purpose, we selected exendin-4 as the lead compound and radiolabeled lysine at residue 12 in exendin-4 or additional lysine at the C-terminus using [¹²³I]iodobenzoylation. To evaluate in vitro receptor specificity, binding assay was performed using dispersed mouse islet cells. Biodistribution study was performed in normal ddY mice. Ex vivo autoradiography was performed in transgenic mice expressing green fluorescent protein under control of the mouse insulin I gene promoter. Additionally, SPECT imaging was performed in normal ddY mice. The affinity of novel synthesized derivatives toward pancreatic β-cells was not affected by iodobenzoylation. The derivatives accumulated in the pancreas after intravenous administration specifically via GLP-1R expressed on the pancreatic β-cells. Extremely high signal-to-noise ratio was observed during evaluation of biodistribution of [¹²³I]IB12-Ex4. SPECT images using normal mice showed that [¹²³I]IB12-Ex4 accumulated in the pancreas with high contrast between the pancreas and background. These results indicate that [¹²³I]IB12-Ex4 for SPECT is useful for clinical applications because of its preferable kinetics in vivo.

Characterisation of Ppy-lineage cells clarifies the functional heterogeneity of pancreatic beta cells in mice

AIMS/HYPOTHESIS

Pancreatic polypeptide (PP) cells, which secrete PP (encoded by the Ppy gene), are a minor population of pancreatic endocrine cells. Although it has been reported that the loss of beta cell identity might be associated with beta-to-PP cell-fate conversion, at present, little is known regarding the characteristics of Ppy-lineage cells.

METHODS

We used Ppy-Cre driver mice and a PP-specific monoclonal antibody to investigate the association between Ppy-lineage cells and beta cells. The molecular profiles of endocrine cells were investigated by single-cell transcriptome analysis and the glucose responsiveness of beta cells was assessed by Ca²⁺ imaging. Diabetic conditions were experimentally induced in mice by either streptozotocin or diphtheria toxin.

RESULTS

Ppy-lineage cells were found to contribute to the four major types of endocrine cells, including beta cells. Ppy-lineage beta cells are a minor subpopulation, accounting for 12-15% of total beta cells, and are mostly (81.2%) localised at the islet periphery. Unbiased single-cell analysis with a Ppy-lineage tracer demonstrated that beta cells are composed of seven clusters, which are categorised into two groups (i.e. Ppy-lineage and non-Ppy-lineage beta cells). These subpopulations of beta cells demonstrated distinct characteristics regarding their functionality and gene expression profiles. Ppy-lineage beta cells had a reduced glucose-stimulated Ca²⁺ signalling response and were increased in number in experimental diabetes models.

CONCLUSIONS/INTERPRETATION

Our results indicate that an unexpected degree of beta cell heterogeneity is defined by Ppy gene activation, providing valuable insight into the homeostatic regulation of pancreatic islets and future therapeutic strategies against diabetes.

DATA AVAILABILITY

The single-cell RNA sequence (scRNA-seq) analysis datasets generated in this study have been deposited in the Gene Expression Omnibus (GEO) under the accession number GSE166164 ( www.ncbi.nlm.nih.gov/geo/query/acc.cgi?acc=GSE166164 ).

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.

In Vivo and In Situ Approach to Study Islet Microcirculation: A Mini-Review

The pancreas is regarded as consisting of two separate organ systems, the endocrine and exocrine pancreas. While treatment of a disease with either an endocrine or exocrine pathogenesis may affect the function of the entire pancreas, the pancreatic diseases have been treated by clinicians in different medical disciplines, including endocrinologists and gastroenterologists. Islet microcirculation has long been considered to be regulated independently from that of the exocrine pancreas. A new model proposes that pancreatic islet blood flow is integrated with the surrounding exocrine capillary network. This recent model may provide revived or contrasting hypotheses to test, since the pancreatic microcirculation has critical implications for the regulation of islet hormones as well as acinar pancreas functions. In this mini-review, practical applications of in vivo and in situ studies of islet microcirculation are described with a specific emphasis on large-scale data analysis to ensure sufficient sample size accounting for known islet heterogeneity. For in vivo small animal studies, intravital microscopy based on two-photon excitation microscopes is a powerful tool that enables capturing the flow direction and speed of individual fluorescent-labeled red blood cells. Complementarily, for structural analysis of blood vessels, the recent technical advancements of confocal microscopy and tissue clearing have enabled us to image the three-dimensional network structure in thick tissue slices.

Temporal Transcriptome Analysis Reveals Dynamic Gene Expression Patterns Driving β-Cell Maturation

Newly differentiated pancreatic β cells lack proper insulin secretion profiles of mature functional β cells. The global gene expression differences between paired immature and mature β cells have been studied, but the dynamics of transcriptional events, correlating with temporal development of glucose-stimulated insulin secretion (GSIS), remain to be fully defined. This aspect is important to identify which genes and pathways are necessary for β-cell development or for maturation, as defective insulin secretion is linked with diseases such as diabetes. In this study, we assayed through RNA sequencing the global gene expression across six β-cell developmental stages in mice, spanning from β-cell progenitor to mature β cells. A computational pipeline then selected genes differentially expressed with respect to progenitors and clustered them into groups with distinct temporal patterns associated with biological functions and pathways. These patterns were finally correlated with experimental GSIS, calcium influx, and insulin granule formation data. Gene expression temporal profiling revealed the timing of important biological processes across β-cell maturation, such as the deregulation of β-cell developmental pathways and the activation of molecular machineries for vesicle biosynthesis and transport, signal transduction of transmembrane receptors, and glucose-induced Ca²⁺ influx, which were established over a week before β-cell maturation completes. In particular, β cells developed robust insulin secretion at high glucose several days after birth, coincident with the establishment of glucose-induced calcium influx. Yet the neonatal β cells displayed high basal insulin secretion, which decreased to the low levels found in mature β cells only a week later. Different genes associated with calcium-mediated processes, whose alterations are linked with insulin resistance and deregulation of glucose homeostasis, showed increased expression across β-cell stages, in accordance with the temporal acquisition of proper GSIS. Our temporal gene expression pattern analysis provided a comprehensive database of the underlying molecular components and biological mechanisms driving β-cell maturation at different temporal stages, which are fundamental for better control of the in vitro production of functional β cells from human embryonic stem/induced pluripotent cell for transplantation-based type 1 diabetes therapy.

ZIGIR, a Granule-Specific Zn2+ Indicator, Reveals Human Islet α Cell Heterogeneity

Numerous mammalian cells contain abundant Zn²⁺ in their secretory granules, yet available Zn²⁺ sensors lack the desired specificity and sensitivity for imaging granular Zn²⁺. We developed a fluorescent zinc granule indicator, ZIGIR, that possesses numerous desired properties for live cell imaging, including >100-fold fluorescence enhancement, membrane permeability, and selective enrichment to acidic granules. The combined advantages endow ZIGIR with superior sensitivity and specificity for imaging granular Zn²⁺. ZIGIR enables separation of heterogenous β cells based on their insulin content and sorting of mouse islets into pure α cells and β cells. In human islets, ZIGIR facilitates sorting of endocrine cells into highly enriched α cells and β cells, reveals unexpectedly high Zn²⁺ activity in the somatostatin granule of some δ cells, and uncovers variation in the glucagon content among human α cells. We expect broad applications of ZIGIR for studying Zn²⁺ biology and Zn²⁺-rich secretory granules and for engineering β cells with high insulin content for treating diabetes.

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.

Coordinated interactions between endothelial cells and macrophages in the islet microenvironment promote β cell regeneration

Endogenous β cell regeneration could alleviate diabetes, but proliferative stimuli within the islet microenvironment are incompletely understood. We previously found that β cell recovery following hypervascularization-induced β cell loss involves interactions with endothelial cells (ECs) and macrophages (MΦs). Here we show that proliferative ECs modulate MΦ infiltration and phenotype during β cell loss, and recruited MΦs are essential for β cell recovery. Furthermore, VEGFR2 inactivation in quiescent ECs accelerates islet vascular regression during β cell recovery and leads to increased β cell proliferation without changes in MΦ phenotype or number. Transcriptome analysis of β cells, ECs, and MΦs reveals that β cell proliferation coincides with elevated expression of extracellular matrix remodeling molecules and growth factors likely driving activation of proliferative signaling pathways in β cells. Collectively, these findings suggest a new β cell regeneration paradigm whereby coordinated interactions between intra-islet MΦs, ECs, and extracellular matrix mediate β cell self-renewal.

A developmental lineage-based gene co-expression network for mouse pancreatic β-cells reveals a role for Zfp800 in pancreas development

To gain a deeper understanding of pancreatic β-cell development, we used iterative weighted gene correlation network analysis to calculate a gene co-expression network (GCN) from 11 temporally and genetically defined murine cell populations. The GCN, which contained 91 distinct modules, was then used to gain three new biological insights. First, we found that the clustered protocadherin genes are differentially expressed during pancreas development. Pcdhγ genes are preferentially expressed in pancreatic endoderm, Pcdhβ genes in nascent islets, and Pcdhα genes in mature β-cells. Second, after extracting sub-networks of transcriptional regulators for each developmental stage, we identified 81 zinc finger protein (ZFP) genes that are preferentially expressed during endocrine specification and β-cell maturation. Third, we used the GCN to select three ZFPs for further analysis by CRISPR mutagenesis of mice. Zfp800 null mice exhibited early postnatal lethality, and at E18.5 their pancreata exhibited a reduced number of pancreatic endocrine cells, alterations in exocrine cell morphology, and marked changes in expression of genes involved in protein translation, hormone secretion and developmental pathways in the pancreas. Together, our results suggest that developmentally oriented GCNs have utility for gaining new insights into gene regulation during organogenesis.

Proinflammatory Cytokine Interleukin 1β Disrupts β-cell Circadian Clock Function and Regulation of Insulin Secretion

Intrinsic β-cell circadian clocks are important regulators of insulin secretion and overall glucose homeostasis. Whether the circadian clock in β-cells is perturbed following exposure to prodiabetogenic stressors such as proinflammatory cytokines, and whether these perturbations are featured during the development of diabetes, remains unknown. To address this, we examined the effects of cytokine-mediated inflammation common to the pathophysiology of diabetes, on the physiological and molecular regulation of the β-cell circadian clock. Specifically, we provide evidence that the key diabetogenic cytokine IL-1β disrupts functionality of the β-cell circadian clock and impairs circadian regulation of glucose-stimulated insulin secretion. The deleterious effects of IL-1β on the circadian clock were attributed to impaired expression of key circadian transcription factor Bmal1, and its regulator, the NAD-dependent deacetylase, Sirtuin 1 (SIRT1). Moreover, we also identified that Type 2 diabetes in humans is associated with reduced immunoreactivity of β-cell BMAL1 and SIRT1, suggestive of a potential causative link between islet inflammation, circadian clock disruption, and β-cell failure. These data suggest that the circadian clock in β-cells is perturbed following exposure to proinflammatory stressors and highlights the potential for therapeutic targeting of the circadian system for treatment for β-cell failure in diabetes.

Induction of Core Circadian Clock Transcription Factor Bmal1 Enhances β-Cell Function and Protects Against Obesity-Induced Glucose Intolerance

Type 2 diabetes mellitus (T2DM) is characterized by β-cell dysfunction as a result of impaired glucose-stimulated insulin secretion (GSIS). Studies show that β-cell circadian clocks are important regulators of GSIS and glucose homeostasis. These observations raise the question about whether enhancement of the circadian clock in β-cells will confer protection against β-cell dysfunction under diabetogenic conditions. To test this, we used an approach by first generating mice with β-cell-specific inducible overexpression of Bmal1 (core circadian transcription factor; β-Bmal1 ^OV ). We subsequently examined the effects of β-Bmal1 ^OV on the circadian clock, GSIS, islet transcriptome, and glucose metabolism in the context of diet-induced obesity. We also tested the effects of circadian clock-enhancing small-molecule nobiletin on GSIS in mouse and human control and T2DM islets. We report that β-Bmal1 ^OV mice display enhanced islet circadian clock amplitude and augmented in vivo and in vitro GSIS and are protected against obesity-induced glucose intolerance. These effects were associated with increased expression of purported BMAL1-target genes mediating insulin secretion, processing, and lipid metabolism. Furthermore, exposure of isolated islets to nobiletin enhanced β-cell secretory function in a Bmal1-dependent manner. This work suggests therapeutic targeting of the circadian system as a potential strategy to counteract β-cell failure under diabetogenic conditions.

Generation of Functional Insulin-Producing Cells from Mouse Embryonic Stem Cells Through Protein Transduction of Transcription Factors

In this chapter, we describe a simple and unique method for the differentiation of mouse embryonic stem cells into insulin-producing cells. In addition to cytokines and growth factors, key transcription factors for pancreatic development are applied in this method through protein transduction technology. Furthermore, a combination of nanofiber plates and laminin coatings improves the yield of differentiated cells. The insulin-producing cells derived through this method express marker genes of mature β-cells and have an ability to secrete insulin; therefore, these cells are useful for fundamental studies on pancreatic development, drug development, and regenerative medicine for diabetes.

Pancreatic Islets and Gestalt Principles

The human brain has inherent methodology to efficiently interpret complex environmental stimuli into understanding. This visual perception is governed by the law of simplicity, which is fundamental to Gestalt theory. First introduced in a seminal article by Wertheimer in 1923, the theory explains how the mind groups similar images and fills in gaps in order to perceive an amenable version of reality. The world we see consists of complex visual scenes, but rarely is the entire picture visible to us. Since it is inefficient for all visual data to be analyzed at once, certain patterns are given higher importance and made to stand out from the rest of the field in our brain. Here we propose that Gestalt theory may explain why rodent islet architecture has historically been seen as having a core-mantle arrangement. By filling in apparent gaps in the non-β-cell lining, the mind interprets it as a "whole" mantle, which may have further led to widely accepted notions regarding islet microcirculation, intra-islet signaling, and islet development. They are largely based on the prevailing stereotypic islet architecture in which an enclosed structure is presumed. Three-dimensional analysis provides more integrated views of islet and pancreatic microcirculation.

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).

Integrated Pancreatic Blood Flow: Bidirectional Microcirculation Between Endocrine and Exocrine Pancreas

The pancreatic islet is a highly vascularized endocrine micro-organ. The unique architecture of rodent islets, a so-called core-mantle arrangement seen in two-dimensional images, led researchers to seek functional implications for islet hormone secretion. Three models of islet blood flow were previously proposed, all based on the assumption that islet microcirculation occurs in an enclosed structure. Recent electrophysiological and molecular biological studies using isolated islets also presumed unidirectional flow. Using intravital analysis of the islet microcirculation in mice, we found that islet capillaries were continuously integrated to those in the exocrine pancreas, which made the islet circulation rather open, not self-contained. Similarly in human islets, the capillary structure was integrated with pancreatic microvasculature in its entirety. Thus, islet microcirculation has no relation to islet cytoarchitecture, which explains its well-known variability throughout species. Furthermore, tracking fluorescent-labeled red blood cells at the endocrine-exocrine interface revealed bidirectional blood flow, with similar variability in blood flow speed in both the intra- and extra-islet vasculature. To date, the endocrine and exocrine pancreas have been studied separately by different fields of investigators. We propose that the open circulation model physically links both endocrine and exocrine parts of the pancreas as a single organ through the integrated vascular network.

SMAD7 enhances adult β-cell proliferation without significantly affecting β-cell function in mice

The interplay between the transforming growth factor β (TGF-β) signaling proteins, SMAD family member 2 (SMAD2) and 3 (SMAD3), and the TGF-β-inhibiting SMAD, SMAD7, seems to play a vital role in proper pancreatic endocrine development and also in normal β-cell function in adult pancreatic islets. Here, we generated conditional SMAD7 knockout mice by crossing insulin1^Cre mice with SMAD7^fx/fx mice. We also created a β cell-specific SMAD7-overexpressing mouse line by crossing insulin1^Dre mice with HPRT-SMAD7/RosaGFP mice. We analyzed β-cell function in adult islets when SMAD7 was either absent or overexpressed in β cells. Loss of SMAD7 in β cells inhibited proliferation, and SMAD7 overexpression enhanced cell proliferation. However, alterations in basic glucose homeostasis were not detectable following either SMAD7 deletion or overexpression in β cells. Our results show that both the absence and overexpression of SMAD7 affect TGF-β signaling and modulates β-cell proliferation but does not appear to alter β-cell function. Reversible SMAD7 overexpression may represent an attractive therapeutic option to enhance β-cell proliferation without negative effects on β-cell function.

Placental growth factor in beta cells plays an essential role in gestational beta-cell growth

OBJECTIVE

Pancreatic beta cells proliferate in response to metabolic requirements during pregnancy, while failure of this response may cause gestational diabetes. A member of the vascular endothelial growth factor family, placental growth factor (PlGF), typically plays a role in metabolic disorder and pathological circumstance. The expression and function of PlGF in the endocrine pancreas have not been reported and are addressed in the current study.

RESEARCH DESIGN AND METHODS

PlGF levels in beta cells were determined by immunostaining or ELISA in purified beta cells in non-pregnant and pregnant adult mice. An adeno-associated virus (AAV) serotype 8 carrying a shRNA for PlGF under the control of a rat insulin promoter (AAV-rat insulin promoter (RIP)-short hairpin small interfering RNA for PlGF (shPlGF)) was prepared and infused into mouse pancreas through the pancreatic duct to specifically knock down PlGF in beta cells, and its effects on beta-cell growth were determined by beta-cell proliferation, beta-cell mass and insulin release. A macrophage-depleting reagent, clodronate, was coapplied into AAV-treated mice to study crosstalk between beta cells and macrophages.

RESULTS

PlGF is exclusively produced by beta cells in the adult mouse pancreas. Moreover, PlGF expression in beta cells was significantly increased during pregnancy. Intraductal infusion of AAV-RIP-shPlGF specifically knocked down PlGF in beta cells, resulting in compromised beta-cell proliferation, reduced growth in beta-cell mass and impaired glucose tolerance during pregnancy. Mechanistically, PlGF depletion in beta cells reduced islet infiltration of trophic macrophages, which appeared to be essential for gestational beta-cell growth.

CONCLUSIONS

Our study suggests that increased expression of PlGF in beta cells may trigger gestational beta-cell growth through recruited macrophages.

A Novel Pancreatic Imaging Window for Stabilized Longitudinal In Vivo Observation of Pancreatic Islets in Murine Model

Longitudinal imaging of murine pancreas is technically challenging due to the mechanical softness of the tissue influenced by peristalsis. Here, we report a novel pancreatic imaging window for long-term stabilized cellular-level observation of the islets in the pancreas in vivo. By spatially separating the pancreas from the bowel movement and physiologic respiration with a metal plate integrated in the imaging window, we successfully tracked the pancreatic islets up to three weeks and visualized the dumbbell-shape transformation from the single islet. This window can be a useful tool for long-term cellular-level visualization of the microstructure in the pancreas.

Integration of Primary Endocrine Cells and Supportive Cells Using Functionalized Silk Promotes the Formation of Prevascularized Islet-like Clusters

Pancreatic islet transplantation has not yet succeeded as an overall treatment for type 1 diabetes because of limited access to donor islets, as well as low efficacy and poor reproducibility of the current procedure. Herein, a method to create islets-like composite clusters (coclusters) from dispersed endocrine cells and supportive cells is described, attempting to improve compatibility with the recipient and more efficiently make use of the donor-derived material. To mimic the extracellular matrix environment, recombinant spider silk functionalized with cell binding motifs are used as 3D support for the coclusters. A cell binding motif derived from fibronectin (FN) was found superior in promoting cell adherence, while a plain RGD-motif incorporated in the repetitive part of the silk protein (2R) increased the mobility and cluster formation of endocrine cells. Self-assembly of a mixture of FN/2R silk is utilized to integrate endocrine cells together with endothelial and mesenchymal cells into islet-like coclusters. Both xenogenic and allogenic versions of these coclusters were found to be viable and were able to respond to dynamic glucose stimulation with insulin release. Moreover, the endothelial cells were found to be colocalized with the endocrine cells, showing that the silk combined with supportive cells may promote vascularization. This method to engineer combined islet-like coclusters allows donor-derived endocrine cells to be surrounded by supportive cells from the recipient, which have the potential to further promote engraftment in the host and considerably reduce risk of rejection.

Generating Beta-Cell-Specific Transgenic Mice Using the Cre-Lox System

Beta-cell-specific transgenic mice provide an invaluable model for dissecting the direct signaling mechanisms involved in regulating beta-cell structure and function. Furthermore, generating novel transgenic models is now easier and more cost-effective than ever, thanks to exciting novel approaches such as CRISPR.Here, we describe the commonly used approaches for generating and maintaining beta-cell-specific transgenic models and some of the considerations involved in their use. This includes the use of different beta-cell-specific promoters (e.g., pancreatic and duodenal homeobox factor 1 (Pdx1), rat insulin 2 promoter (RIP), and mouse insulin 1 promoter (MIP)) to drive site-specific recombinase technology. Important considerations during selection include level and uniformity of expression in the beta-cell population, ectopic transgene expression, and the use of inducible models.This chapter provides a guide to the procurement, generation, and maintenance of a beta-cell-specific transgene colony from preexisting Cre and loxP mouse strains, providing methods for crossbreeding and genotyping, as well as subsequent maintenance and, in the case of inducible models, transgenic induction.

Navigating the Depths and Avoiding the Shallows of Pancreatic Islet Cell Transcriptomes

Islet gene expression has been widely studied to better understand the transcriptional features that define a healthy β-cell. Transcriptomes of FACS-purified α-, β-, and δ-cells using bulk RNA-sequencing have facilitated our understanding of the complex network of cross talk between islet cells and its effects on β-cell function. However, these approaches were by design not intended to resolve heterogeneity between individual cells. Several recent studies used single-cell RNA sequencing (scRNA-Seq) to report considerable heterogeneity within mouse and human β-cells. In this Perspective, we assess how this newfound ability to assess gene expression at single-cell resolution has enhanced our understanding of β-cell heterogeneity. We conduct a comprehensive assessment of several single human β-cell transcriptome data sets and ask if the heterogeneity reported by these studies showed overlap and concurred with previously known examples of β-cell heterogeneity. We also illustrate the impact of the inevitable limitations of working at or below the limit of detection of gene expression at single cell resolution and their consequences for the quality of single-islet cell transcriptome data. Finally, we offer some guidance on when to opt for scRNA-Seq and when bulk sequencing approaches may be better suited.

Tools for Bioimaging Pancreatic β Cells in Diabetes

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

Increased risk for T cell autoreactivity to ß-cell antigens in the mice expressing the Avy obesity-associated gene

There has been considerable debate as to whether obesity can act as an accelerator of type 1 diabetes (T1D). We assessed this possibility using transgenic mice (MIP-TF mice) whose ß-cells express enhanced green fluorescent protein (EGFP). Infecting these mice with EGFP-expressing murine herpes virus-68 (MHV68-EGFP) caused occasional transient elevation in their blood glucose, peri-insulitis, and Th1 responses to EGFP which did not spread to other ß-cell antigens. We hypothesized that obesity-related systemic inflammation and ß-cell stress could exacerbate the MHV68-EGFP-induced ß-cell autoreactivity. We crossed MIP-TF mice with A^vy mice which develop obesity and provide models of metabolic disease alongside early stage T2D. Unlike their MIP-TF littermates, MHV68-EGFP-infected A^vy/MIP-TF mice developed moderate intra-insulitis and transient hyperglycemia. MHV68-EGFP infection induced a more pronounced intra-insulitis in older, more obese, A^vy/MIP-TF mice. Moreover, in MHV68-EGFP-infected A^vy/MIP-TF mice, Th1 reactivity spread from EGFP to other ß-cell antigens. Thus, the spreading of autoreactivity among ß-cell antigens corresponded with the transition from peri-insulitis to intra-insulitis and occurred in obese A^vy/MIP-TF mice but not lean MIP-TF mice. These observations are consistent with the notion that obesity-associated systemic inflammation and ß-cell stress lowers the threshold necessary for T cell autoreactivity to spread from EGFP to other ß-cell autoantigens.

p120ctn-Mediated Organ Patterning Precedes and Determines Pancreatic Progenitor Fate

The mechanism of how organ shape emerges and specifies cell fate is not understood. Pancreatic duct and endocrine lineages arise in a spatially distinct domain from the acinar lineage. Whether these lineages are pre-determined or settle once these niches have been established remains unknown. Here, we reconcile these two apparently opposing models, demonstrating that pancreatic progenitors re-localize to establish the niche that will determine their ultimate fate. We identify a p120ctn-regulated mechanism for coordination of organ architecture and cellular fate mediated by differential E-cadherin based cell sorting. Reduced p120ctn expression is necessary and sufficient to re-localize a subset of progenitors to the peripheral tip domain, where they acquire an acinar fate. The same mechanism is used re-iteratively during endocrine specification, where it balances the choice between the alpha and beta cell fates. In conclusion, organ patterning is regulated by p120ctn-mediated cellular positioning, which precedes and determines pancreatic progenitor fate.

Single-Cell RNA-Seq of the Pancreatic Islets--a Promise Not yet Fulfilled?

In the past 3 years, we have seen a flurry of publications on single-cell RNA sequencing (RNA-seq) analyses of pancreatic islets from mouse and human. This technology holds the promise to refine cell-type signatures and discover cellular heterogeneity among the canonical endocrine cell types such as the glucagon-producing α and insulin-producing β cells, going as far as suggesting new subtypes. In addition, single-cell RNA-seq has the ability to characterize rare endocrine cell types that are not captured by prior bulk analysis. With transcriptomics data from individual endocrine cells, cellular states can be profiled both along developmental processes and during the emergence of metabolic diseases. However, the promises of this new technology have not yet been met in full. While the methodology for the first time enabled the transcriptional definition of rare endocrine cell types such as ghrelin-producing ɛ cells, some of the conclusions regarding cell-type-specific gene expression changes in type 2 diabetes might need to be revisited once larger sample sizes become available. Data generation and analysis are continuously improving single-cell RNA-seq approaches and are helping us to understand the (mal)adaptations of the islet cells during development, metabolic challenge, and disease.

Transgene-associated human growth hormone expression in pancreatic β-cells impairs identification of sex-based gene expression differences

Fluorescent protein reporter genes are widely used to identify and sort murine pancreatic β-cells. In this study, we compared use of the MIP-GFP transgene, which exhibits aberrant expression of human growth hormone (hGH), with a newly derived Ins2^Apple allele that lacks hGH expression on the expression of sex-specific genes. β-Cells from MIP-GFP transgenic mice exhibit changes in the expression of 7,733 genes, or greater than half of their transcriptome, compared with β-cells from Ins2^Apple/+ mice. To determine how these differences might affect a typical differential gene expression study, we analyzed the effect of sex on gene expression using both reporter lines. Six hundred fifty-seven differentially expressed genes were identified between male and female β-cells containing the Ins2^Apple allele. Female β-cells exhibit higher expression of Xist, Tmed9, Arpc3, Eml2, and several islet-enriched transcription factors, including Nkx2-2 and Hnf4a, whereas male β-cells exhibited a generally higher expression of genes involved in cell cycle regulation. In marked contrast, the same male vs. female comparison of β-cells containing the MIP-GFP transgene revealed only 115 differentially expressed genes, and comparison of the 2 lists of differentially expressed genes revealed only 17 that were common to both analyses. These results indicate that 1) male and female β-cells differ in their expression of key transcription factors and cell cycle regulators and 2) the MIP-GFP transgene may attenuate sex-specific differences that distinguish male and female β-cells, thereby impairing the identification of sex-specific variations.

Tissue curvature and apicobasal mechanical tension imbalance instruct cancer morphogenesis

Tubular epithelia are a basic building block of organs and a common site of cancer occurrence1-4. During tumorigenesis, transformed cells overproliferate and epithelial architecture is disrupted. However, the biophysical parameters that underlie the adoption of abnormal tumour tissue shapes are unknown. Here we show in the pancreas of mice that the morphology of epithelial tumours is determined by the interplay of cytoskeletal changes in transformed cells and the existing tubular geometry. To analyse the morphological changes in tissue architecture during the initiation of cancer, we developed a three-dimensional whole-organ imaging technique that enables tissue analysis at single-cell resolution. Oncogenic transformation of pancreatic ducts led to two types of neoplastic growth: exophytic lesions that expanded outwards from the duct and endophytic lesions that grew inwards to the ductal lumen. Myosin activity was higher apically than basally in wild-type cells, but upon transformation this gradient was lost in both lesion types. Three-dimensional vertex model simulations and a continuum theory of epithelial mechanics, which incorporate the cytoskeletal changes observed in transformed cells, indicated that the diameter of the source epithelium instructs the morphology of growing tumours. Three-dimensional imaging revealed that-consistent with theory predictions-small pancreatic ducts produced exophytic growth, whereas large ducts deformed endophytically. Similar patterns of lesion growth were observed in tubular epithelia of the liver and lung; this finding identifies tension imbalance and tissue curvature as fundamental determinants of epithelial tumorigenesis.

The eye as a novel imaging site in diabetes research

Diabetes develops due to deficient functional β cell mass, insulin resistance, or both. Yet, various challenges in understanding the mechanisms underlying diabetes development in vivo remain to be overcome owing to the lack of appropriate intravital imaging technologies. To meet these challenges, we have exploited the anterior chamber of the eye (ACE) as a novel imaging site to understand diabetes basics and clinics in vivo. We have developed a technology platform transplanting pancreatic islets into the ACE where they later on can be imaged non-invasively for long time. It turns out that the ACE serves as an optimal imaging site and provides implanted islets with an oxygen-rich milieu and an immune-privileged niche where they undergo optimal engraftment, rich vascularization and dense innervation, preserve organotypic features and live with satisfactory viability and functionality. The ACE technology has led to a series of significant observations. It enables in vivo microscopy of islet cytoarchitecture, function and viability in the physiological context and intravital imaging of a variety of pathological events such as autoimmune insulitis, defects in β cell function and mass and insulin resistance during diabetes development in a real-time manner. Furthermore, application of the ACE technology in humanized mice and non-human primates verifies translational and clinical values of the technology. In this article, we describe the ACE technology in detail, review accumulated knowledge gained by means of the ACE technology and delineate prospective avenues for the ACE technology.

Adrb2 controls glucose homeostasis by developmental regulation of pancreatic islet vasculature

A better understanding of processes controlling the development and function of pancreatic islets is critical for diabetes prevention and treatment. Here, we reveal a previously unappreciated function for pancreatic β2-adrenergic receptors (Adrb2) in controlling glucose homeostasis by restricting islet vascular growth during development. Pancreas-specific deletion of Adrb2 results in glucose intolerance and impaired insulin secretion in mice, and unexpectedly, specifically in females. The metabolic phenotypes were recapitulated by Adrb2 deletion from neonatal, but not adult, β-cells. Mechanistically, Adrb2 loss increases production of Vascular Endothelial Growth Factor-A (VEGF-A) in female neonatal β-cells and results in hyper-vascularized islets during development, which in turn, disrupts insulin production and exocytosis. Neonatal correction of islet hyper-vascularization, via VEGF-A receptor blockade, fully rescues functional deficits in glucose homeostasis in adult mutant mice. These findings uncover a regulatory pathway that functions in a sex-specific manner to control glucose metabolism by restraining excessive vascular growth during islet development.

Insulin Is Transcribed and Translated in Mammalian Taste Bud Cells

We and others have reported that taste cells in taste buds express many peptides in common with cells in the gut and islets of Langerhans in the pancreas. Islets and taste bud cells express the hormones glucagon and ghrelin, the same ATP-sensitive potassium channel responsible for depolarizing the insulin-secreting β cell during glucose-induced insulin secretion, as well as the propeptide-processing enzymes PC1/3 and PC2. Given the common expression of functionally specific proteins in taste buds and islets, it is surprising that no one has investigated whether insulin is synthesized in taste bud cells. Using immunofluorescence, we demonstrated the presence of insulin in mouse, rat, and human taste bud cells. By detecting the postprocessing insulin molecule C-peptide and green fluorescence protein (GFP) in taste cells of both insulin 1-GFP and insulin 2-GFP mice and the presence of the mouse insulin transcript by in situ hybridization, we further proved that insulin is synthesized in individual taste buds and not taken up from the parenchyma. In addition to our cytology data, we measured the level of insulin transcript by quantitative RT-PCR in the anterior and posterior lingual epithelia. These analyses showed that insulin is translated in the circumvallate and foliate papillae in the posterior, but only insulin transcript was detected in the anterior fungiform papillae of the rodent tongue. Thus, some taste cells are insulin-synthesizing cells generated from a continually replenished source of precursor cells in the adult mammalian lingual epithelium.

Generation of Scaffold-free, Three-dimensional Insulin Expressing Pancreatoids from Mouse Pancreatic Progenitors In Vitro

The pancreas is a complex organ composed of many different cell types that work together to regulate blood glucose homeostasis and digestion. These cell types include enzyme-secreting acinar cells, an arborized ductal system responsible for the transportation of enzymes to the gut, and hormone-producing endocrine cells. Endocrine beta-cells are the sole cell type in the body that produce insulin to lower blood glucose levels. Diabetes, a disease characterized by a loss or the dysfunction of beta-cells, is reaching epidemic proportions. Thus, it is essential to establish protocols to investigate beta-cell development that can be used for screening purposes to derive the drug and cell-based therapeutics. While the experimental investigation of mouse development is essential, in vivo studies are laborious and time-consuming. Cultured cells provide a more convenient platform for screening; however, they are unable to maintain the cellular diversity, architectural organization, and cellular interactions found in vivo. Thus, it is essential to develop new tools to investigate pancreatic organogenesis and physiology. Pancreatic epithelial cells develop in the close association with mesenchyme from the onset of organogenesis as cells organize and differentiate into the complex, physiologically competent adult organ. The pancreatic mesenchyme provides important signals for the endocrine development, many of which are not well understood yet, thus difficult to recapitulate during the in vitro culture. Here, we describe a protocol to culture three-dimensional, cellular complex mouse organoids that retain mesenchyme, termed pancreatoids. The e10.5 murine pancreatic bud is dissected, dissociated, and cultured in a scaffold-free environment. These floating cells self-assemble with mesenchyme enveloping the developing pancreatoid and a robust number of endocrine beta-cells developing along with the acinar and the duct cells. This system can be used to study the cell fate determination, structural organization, and morphogenesis, cell-cell interactions during organogenesis, or for the drug, small molecule, or genetic screening.

Expansion of transplanted islets in mice by co-transplantation with adipose tissue-derived mesenchymal stem cells

The shortage of donor islets is a significant obstacle for widespread clinical application of pancreatic islet transplantation. To investigate whether adipose tissue-derived mesenchymal stem cells (ADSCs) induce expansion of transplanted islets, we performed co-transplantation experiments in a mouse model. Streptozotosin (STZ)-induced diabetic mice transplanted with 50 syngeneic islets remained hyperglycemic. However, hyperglycemia was ameliorated gradually when 50 islets were co-transplanted with ADSCs but not separately grafted into the contralateral kidney. Insulin and proinsulin contents of 120-day grafts containing 50 islets co-transplanted with ADSCs were significantly increased compared with those of 50 isolated islets. The Ki67-positive ratios in islets of the naïve pancreas, at 30 and 120 days grafts were 0.23%, 2.12%, and 1.52%, respectively. Ki67-positive cells were predominantly Pdx1+ and insulin+ cells. These results demonstrate that co-transplantation with ADSCs induces proliferation of transplanted islets in mice, suggesting a potential solution for the low efficiency of islet transplantation.

Optical clearing of the pancreas for visualization of mature β-cells and vessels in mice

Glucose metabolism is regulated by insulin, which is produced from β-cells in the pancreas. Because insulin is secreted into vessels in response to blood glucose, vascular structures of the pancreas, especially the relationship between vessels and β-cells, are important for physiological and pathological glucose metabolism. Here, we developed a system to visualize vessels surrounding mature β-cells expressing transcription factor MafA in a three-dimensional manner. Optical clearing of the pancreas prevented light scattering of fluorescence driven by the bacterial artificial chromosome (BAC)-mafA promoter in β-cells. Reconstruction of confocal images demonstrated mature β-cells and the glomerular-like structures of β-cell vasculatures labeled with DyLight 488-conjugated lectin in normal mice as well as in low-dose streptozotocin-injected diabetes model mice with reduced β-cell mass. This technological innovation of organ imaging can be used to investigate morphological changes in vascular structures during transplantation, regeneration and diabetes development.