Impaired migration and delayed differentiation of pancreatic islet cells in mice lacking EGF-receptors

Receptors and Signaling Pathways Controlling Beta-Cell Function and Survival as Targets for Anti-Diabetic Therapeutic Strategies

Preserving the function and survival of pancreatic beta-cells, in order to achieve long-term glycemic control and prevent complications, is an essential feature for an innovative drug to have clinical value in the treatment of diabetes. Innovative research is developing therapeutic strategies to prevent pathogenic mechanisms and protect beta-cells from the deleterious effects of inflammation and/or chronic hyperglycemia over time. A better understanding of receptors and signaling pathways, and of how they interact with each other in beta-cells, remains crucial and is a prerequisite for any strategy to develop therapeutic tools aimed at modulating beta-cell function and/or mass. Here, we present a comprehensive review of our knowledge on membrane and intracellular receptors and signaling pathways as targets of interest to protect beta-cells from dysfunction and apoptotic death, which opens or could open the way to the development of innovative therapies for diabetes.

A splice site variant in MADD affects hormone expression in pancreatic β cells and pituitary gonadotropes

MAPK activating death domain (MADD) is a multifunctional protein regulating small GTPases RAB3 and RAB27, MAPK signaling, and cell survival. Polymorphisms in the MADD locus are associated with glycemic traits, but patients with biallelic variants in MADD manifest a complex syndrome affecting nervous, endocrine, exocrine, and hematological systems. We identified a homozygous splice site variant in MADD in 2 siblings with developmental delay, diabetes, congenital hypogonadotropic hypogonadism, and growth hormone deficiency. This variant led to skipping of exon 30 and in-frame deletion of 36 amino acids. To elucidate how this mutation causes pleiotropic endocrine phenotypes, we generated relevant cellular models with deletion of MADD exon 30 (dex30). We observed reduced numbers of β cells, decreased insulin content, and increased proinsulin-to-insulin ratio in dex30 human embryonic stem cell-derived pancreatic islets. Concordantly, dex30 led to decreased insulin expression in human β cell line EndoC-βH1. Furthermore, dex30 resulted in decreased luteinizing hormone expression in mouse pituitary gonadotrope cell line LβT2 but did not affect ontogeny of stem cell-derived GnRH neurons. Protein-protein interactions of wild-type and dex30 MADD revealed changes affecting multiple signaling pathways, while the GDP/GTP exchange activity of dex30 MADD remained intact. Our results suggest MADD-specific processes regulate hormone expression in pancreatic β cells and pituitary gonadotropes.

Membrane protease prostasin promotes insulin secretion by regulating the epidermal growth factor receptor pathway

Prostasin (PRSS8) is a serine protease that metabolizes and moderates the effect of specific substrates. Epidermal growth factor receptor (EGFR), which modulates insulin secretion and pancreatic β-cell proliferation, is regulated via proteolytic shedding by PRSS8. We first detected PRSS8 expression in β-cells of pancreatic islets of mice. To better understand the molecular processes involved in PRSS8-associated insulin secretion, pancreatic β-cell-specific PRSS8 knockout (βKO) and PRSS8-overexpressing (βTG) male mice were generated. We found that glucose intolerance and reduction in glucose-stimulated insulin secretion developed in βKO mice compared with the control subjects. A higher response to glucose was noted in islets retrieved from βTG mice. Erlotinib, a specific blocker of EGFR, blocks EGF- and glucose-stimulated secretion of insulin among MIN6 cells, and glucose improves EGF release from β-cells. After silencing PRSS8 in MIN6 cells, glucose-stimulated insulin secretion decreased, and EGFR signaling was impaired. Conversely, overexpression of PRSS8 in MIN6 cells induced higher concentrations of both basal and glucose-stimulated insulin secretion and increased phospho-EGFR concentrations. Furthermore, short-term exposure to glucose improved the concentration of endogenous PRSS8 in MIN6 cells through inhibition of intracellular degradation. These findings suggest that PRSS8 is involved in glucose-dependent physiological regulation of insulin secretion via the EGF-EGFR signaling pathway in pancreatic β-cells.

Heterogeneity of Islet Cells during Embryogenesis and Differentiation

Diabetes is caused by insufficient insulin secretion due to β-cell dysfunction and/or β-cell loss. Therefore, the restoration of functional β-cells by the induction of β-cell differentiation from embryonic stem (ES) and induced-pluripotent stem (iPS) cells, or from somatic non-β-cells, may be a promising curative therapy. To establish an efficient and feasible method for generating functional insulin-producing cells, comprehensive knowledge of pancreas development and β-cell differentiation, including the mechanisms driving cell fate decisions and endocrine cell maturation is crucial. Recent advances in single-cell RNA sequencing (scRNA-seq) technologies have opened a new era in pancreas development and diabetes research, leading to clarification of the detailed transcriptomes of individual insulin-producing cells. Such extensive high-resolution data enables the inference of developmental trajectories during cell transitions and gene regulatory networks. Additionally, advancements in stem cell research have not only enabled their immediate clinical application, but also has made it possible to observe the genetic dynamics of human cell development and maturation in a dish. In this review, we provide an overview of the heterogeneity of islet cells during embryogenesis and differentiation as demonstrated by scRNA-seq studies on the developing and adult pancreata, with implications for the future application of regenerative medicine for diabetes.

Determinants and dynamics of pancreatic islet architecture

The islets of Langerhans are highly organized structures that have species-specific, three-dimensional tissue architecture. Islet architecture is critical for proper hormone secretion in response to nutritional stimuli. Islet architecture is disrupted in all types of diabetes mellitus and in cadaveric islets for transplantation during isolation, culture, and perfusion, limiting patient outcomes. Moreover, recapitulating native islet architecture remains a key challenge for in vitro generation of islets from stem cells. In this review, we discuss work that has led to the current understanding of determinants of pancreatic islet architecture, and how this architecture is maintained or disrupted during tissue remodeling in response to normal and pathological metabolic changes. We further discuss both empirical and modeling data that highlight the importance of islet architecture for islet function.

Optimizing Generation of Stem Cell-Derived Islet Cells

Islet transplantation is a highly effective treatment for select patients with type 1 diabetes. Unfortunately, current use is limited to those with brittle disease due to donor limitations and immunosuppression requirements. Discovery of factors for induction of pluripotent stem cells from adult somatic cells into a malleable state has reinvigorated the possibility of autologous-based regenerative cell therapies. Similarly, recent progress in allogeneic human embryonic stem cell islet products is showing early success in clinical trials. Describing safe and standardized differentiation protocols with clear pathways to optimize yield and minimize off-target growth is needed to efficiently move the field forward. This review discusses current islet differentiation protocols with a detailed break-down of differentiation stages to guide step-wise controlled generation of functional islet products.

A single-cell human islet interactome atlas identifies disrupted autocrine and paracrine communications in type 2 diabetes

A sensible control of hormone secretion from pancreatic islets requires concerted inter-cellular communications, but a comprehensive picture of the whole islet interactome is presently missing. Single-cell transcriptomics allows to overcome this and we used here a single-cell dataset from type 2 diabetic (T2D) and non-diabetic (ND) donors to leverage islet interaction networks. The single-cell dataset contains 3046 cells classified in 7 cell types. The interactions across cell types in T2D and ND were obtained and resulting networks analysed to identify high-centrality genes and altered interactions in T2D. The T2D interactome displayed a higher number of interactions (10 787) than ND (9707); 1289 interactions involved beta cells (1147 in ND). High-centrality genes included EGFR, FGFR1 and FGFR2, important for cell survival and proliferation. In conclusion, this analysis represents the first in silico model of the human islet interactome, enabling the identification of signatures potentially relevant for T2D pathophysiology.

Fetal Programming of the Endocrine Pancreas: Impact of a Maternal Low-Protein Diet on Gene Expression in the Perinatal Rat Pancreas

In rats, the time of birth is characterized by a transient rise in beta cell replication, as well as beta cell neogenesis and the functional maturation of the endocrine pancreas. However, the knowledge of the gene expression during this period of beta cell expansion is incomplete. The aim was to characterize the perinatal rat pancreas transcriptome and to identify regulatory pathways differentially regulated at the whole organ level in the offspring of mothers fed a regular control diet (CO) and of mothers fed a low-protein diet (LP). We performed mRNA expression profiling via the microarray analysis of total rat pancreas samples at embryonic day (E) 20 and postnatal days (P) 0 and 2. In the CO group, pancreas metabolic pathways related to sterol and lipid metabolism were highly enriched, whereas the LP diet induced changes in transcripts involved in RNA transcription and gene regulation, as well as cell migration and apoptosis. Moreover, a number of individual transcripts were markedly upregulated at P0 in the CO pancreas: growth arrest specific 6 (Gas6), legumain (Lgmn), Ets variant gene 5 (Etv5), alpha-fetoprotein (Afp), dual-specificity phosphatase 6 (Dusp6), and angiopoietin-like 4 (Angptl4). The LP diet induced the downregulation of a large number of transcripts, including neurogenin 3 (Neurog3), Etv5, Gas6, Dusp6, signaling transducer and activator of transcription 3 (Stat3), growth hormone receptor (Ghr), prolactin receptor (Prlr), and Gas6 receptor (AXL receptor tyrosine kinase; Axl), whereas upregulated transcripts were related to inflammatory responses and cell motility. We identified differentially regulated genes and transcriptional networks in the perinatal pancreas. These data revealed marked adaptations of exocrine and endocrine in the pancreas to the low-protein diet, and the data can contribute to identifying novel regulators of beta cell mass expansion and functional maturation and may provide a valuable tool in the generation of fully functional beta cells from stem cells to be used in replacement therapy.

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.

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

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

Deletion of pancreas-specific miR-216a reduces beta-cell mass and inhibits pancreatic cancer progression in mice

miRNAs have crucial functions in many biological processes and are candidate biomarkers of disease. Here, we show that miR-216a is a conserved, pancreas-specific miRNA with important roles in pancreatic islet and acinar cells. Deletion of miR-216a in mice leads to a reduction in islet size, β-cell mass, and insulin levels. Single-cell RNA sequencing reveals a subpopulation of β-cells with upregulated acinar cell markers under a high-fat diet. miR-216a is induced by TGF-β signaling, and inhibition of miR-216a increases apoptosis and decreases cell proliferation in pancreatic cells. Deletion of miR-216a in the pancreatic cancer-prone mouse line KrasG12D;Ptf1aCreER reduces the propensity of pancreatic cancer precursor lesions. Notably, circulating miR-216a levels are elevated in both mice and humans with pancreatic cancer. Collectively, our study gives insights into how β-cell mass and acinar cell growth are modulated by a pancreas-specific miRNA and also suggests miR-216a as a potential biomarker for diagnosis of pancreatic diseases.

Pancreas morphogenesis: Branching in and then out

The pancreas of adult mammals displays a branched structure which transports digestive enzymes produced in the distal acini through a tree-like network of ducts into the duodenum. In contrast to several other branched organs, its branching patterns are not stereotypic. Moreover, the branches do not grow from dichotomic splitting of an initial stem but rather from the formation of microlumen in a mass of cells. These lumen progressively assemble into a hyperconnected network that refines into a tree by the time of birth. We review the cell remodeling events and the molecular mechanisms governing pancreas branching, as well as the role of the surrounding tissues in this process. Furthermore, we draw parallels with other branched organs such as the salivary and mammary gland.

Reversal of autoimmunity by mixed chimerism enables reactivation of β cells and transdifferentiation of α cells in diabetic NOD mice

Cure of autoimmune type 1 diabetes (T1D) requires both reversal of autoimmunity and regeneration or resupply of insulin-producing β cells. We have observed that combination therapy with induction of haploidentical mixed chimerism and administration of gastrin and epidermal growth factor (EGF) cures firmly established T1D. The predominant source of β cell regeneration in mice comes from reactivation of dysfunctional insulin^lo β cells and transdifferentiation of α cells. These studies have provided insights into β cell regeneration mechanisms in firmly established autoimmune T1D, in particular, reactivation of the insulin^lo β cells after reversal of autoimmunity by induction of haploidentical mixed chimerism. These studies also provide a preclinical scientific basis for the feasibility of cure of long-standing T1D in humans.

Type 1 diabetes (T1D) results from the autoimmune destruction of β cells, so cure of firmly established T1D requires both reversal of autoimmunity and restoration of β cells. It is known that β cell regeneration in nonautoimmune diabetic mice can come from differentiation of progenitors and/or transdifferentiation of α cells. However, the source of β cell regeneration in autoimmune nonobese diabetic (NOD) mice remains unclear. Here, we show that, after reversal of autoimmunity by induction of haploidentical mixed chimerism, administration of gastrin plus epidermal growth factor augments β cell regeneration and normalizes blood glucose in the firmly established diabetic NOD mice. Using transgenic NOD mice with inducible lineage-tracing markers for insulin-producing β cells, Sox9⁺ ductal progenitors, Nestin⁺ mesenchymal stem cells, and glucagon-producing α cells, we have found that both reactivation of dysfunctional low-level insulin expression (insulin^lo) β cells and neogenesis contribute to the regeneration, with the latter predominantly coming from transdifferentiation of α cells. These results indicate that, after reversal of autoimmunity, reactivation of β cells and transdifferentiation of α cells can provide sufficient new functional β cells to reach euglycemia in firmly established T1D.

A New Perspective in Utilizing MMP-9 as a Therapeutic Target for Alzheimer's Disease and Type 2 Diabetes Mellitus

Matrix metalloprotease 9 (MMP-9) is a 92 kDa type IV collagenase and a member of the family of endopeptidases. MMP-9 is involved in the degradation of extracellular matrix components, tissue remodeling, cellular receptor stripping, and processing of various signaling molecules. In the CNS, the effects of MMP-9 are quite complex, since it exerts beneficial effects including neurogenesis, angiogenesis, myelogenesis, axonal growth, and inhibition of apoptosis, or destructive effects including apoptosis, blood-brain barrier disorder, and demyelination. Likewise, in the periphery, physiological events, as the involvement of MMP-9 in angiogenesis, for instance in wound healing, can be turned into pathological, such as in tumor metastasis, depending on the state of the organism. Alzheimer's disease is a neurodegenerative disorder, characterized by amyloid accumulation and deposition in the brain. Amyloidogenesis, however, also occurs in diseases of the periphery, such as type II diabetes mellitus, where an analogous type of amyloid, is deposited in the pancreas. Interestingly, both diseases exhibit similar pathology and disease progression, with insulin resistance being a major common denominator. Hence, combinatorial strategies searching new or existing molecules to apply for therapeutic use for both diseases are gaining momentum. MMP-9 is extensively studied due to its association with a variety of physiological and pathological processes. Consequently, meticulous design could render MMP-9 into a potential therapeutic target for Alzheimer's disease and type 2 diabetes mellitus; two seemingly unrelated diseases.

Modelling the endocrine pancreas in health and disease

Diabetes mellitus is a multifactorial disease affecting increasing numbers of patients worldwide. Progression to insulin-dependent diabetes mellitus is characterized by the loss or dysfunction of pancreatic β-cells, but the pathomechanisms underlying β-cell failure in type 1 diabetes mellitus and type 2 diabetes mellitus are still poorly defined. Regeneration of β-cell mass from residual islet cells or replacement by β-like cells derived from stem cells holds great promise to stop or reverse disease progression. However, the development of new treatment options is hampered by our limited understanding of human pancreas organogenesis due to the restricted access to primary tissues. Therefore, the challenge is to translate results obtained from preclinical model systems to humans, which requires comparative modelling of β-cell biology in health and disease. Here, we discuss diverse modelling systems across different species that provide spatial and temporal resolution of cellular and molecular mechanisms to understand the evolutionary conserved genotype-phenotype relationship and translate them to humans. In addition, we summarize the latest knowledge on organoids, stem cell differentiation platforms, primary micro-islets and pseudo-islets, bioengineering and microfluidic systems for studying human pancreas development and homeostasis ex vivo. These new modelling systems and platforms have opened novel avenues for exploring the developmental trajectory, physiology, biology and pathology of the human pancreas.

Vitronectin, fibronectin and epidermal growth factor induce proliferation via the JNK and ERK pathways in insulinoma INS-1 cells

An insulinoma is a tumor formed by beta cells in the Langerhans islets of the pancreas. Vitronectin (VTN), fibronectin (FN) and epidermal growth factor (EGF) are important in cell signaling. The aim of this study was to investigate the molecular mechanism that occurs in INS-1 cells with the administration of VTN, FN and EGF in proliferative doses. We determined the proliferative doses of EGF, VTN and FN. The molecular mechanism of proliferation has been investigated alone or in the combination of these proteins. It was observed that INS-1 cells did not have VTN and FN. Cell viability increased with the administration of 0.1 μg/ml VTN, 0.1 μg/ml FN and 1 mg/ml EGF. Proliferation increased with the administration of FN + EGF, and VTN + FN + EGF together when compared to the control group. The total JNK levels did not change between the groups; however, the active JNK levels increased in the VT + FN + EGF group compared to the control group. The total ERK levels increased in the VT + FN + EGF group, and the active ERK levels increased in the VTN + FN, VTN + EGF and VTN + FN + EGF groups compared to the control group. The JNK and ERK pathways are important for proliferation. The JNK and ERK pathways were activated in VTN + FN + EGF administered group. However, it was observed that the ERK pathway was more active than the JNK pathway.

Mutual inhibitions between epidermal growth factor receptor signaling and miR-124a control pancreatic progenitor proliferation

Pancreatic stem/progenitor cells convert from a proliferative to a differentiated fate passing through proliferation cease to a resting state. However, the molecular mechanisms of cell cycle arrest are poorly understood. In this study, we demonstrated that the microRNA-124a (miR-124a) inhibited the proliferation of pancreatic progenitor cells both in vitro and ex vivo and promoted a quiescent state. The miR-124a directly targeted SOS Ras/Rac guanine nucleotide exchange factor 1 (SOS1), IQ motif-containing GTPase-activating protein 1 (IQGAP1), signal transducer and activator of transcription 3 (STAT3), and cyclin D2 (CCND2), thereby inactivating epidermal growth factor receptor (EGFR) downstream signaling pathways including mitogen-activated protein kinase/extracellular signal-regulated kinase (MEK/ERK), phosphatidylinositol 3-kinase-protein kinase B (PI3K/AKT) and Janus kinase (JAK)/STAT3. miR-124a blocked cell proliferation mainly through targeting STAT3 to inhibit PI3K/AKT and JAK/STAT3 signaling. Moreover, miR-124a expression was negatively regulated by EGFR downstream PI3K/AKT signaling. These results indicated that miR-124a and EGFR signaling mutually interact to form a regulating circuit that determines the proliferation of pancreatic progenitor cells.

β-Cell Receptor Tyrosine Kinases in Controlling Insulin Secretion and Exocytotic Machinery: c-Kit and Insulin Receptor

Insulin secretion from pancreatic β-cells is initiated through channel-mediated depolarization, cytoskeletal remodeling, and vesicle tethering at the cell membrane, all of which can be regulated through cell surface receptors. Receptor tyrosine kinases (RTKs) promote β-cell development and postnatal signaling to improve β-cell mass and function, yet their activation has also been shown to initiate exocytotic events in β-cells. This review examines the role of RTK signaling in insulin secretion, with a focus on RTKs c-Kit and insulin receptor (IR). Pathways that control insulin release and the potential interplay between c-Kit and IR signaling are discussed, along with clinical implications of RTK therapy on insulin secretion.

Understanding human fetal pancreas development using subpopulation sorting, RNA sequencing and single-cell profiling

To decipher the populations of cells present in the human fetal pancreas and their lineage relationships, we developed strategies to isolate pancreatic progenitors, endocrine progenitors and endocrine cells. Transcriptome analysis of the individual populations revealed a large degree of conservation among vertebrates in the drivers of gene expression changes that occur at different steps of differentiation, although notably, sometimes, different members of the same gene family are expressed. The transcriptome analysis establishes a resource to identify novel genes and pathways involved in human pancreas development. Single-cell profiling further captured intermediate stages of differentiation and enabled us to decipher the sequence of transcriptional events occurring during human endocrine differentiation. Furthermore, we evaluate how well individual pancreatic cells derived in vitro from human pluripotent stem cells mirror the natural process occurring in human fetuses. This comparison uncovers a few differences at the progenitor steps, a convergence at the steps of endocrine induction, and the current inability to fully resolve endocrine cell subtypes in vitro.

In vivo imaging of emerging endocrine cells reveals a requirement for PI3K-regulated motility in pancreatic islet morphogenesis

The three-dimensional architecture of the pancreatic islet is integral to beta cell function, but the process of islet formation remains poorly understood due to the difficulties of imaging internal organs with cellular resolution. Within transparent zebrafish larvae, the developing pancreas is relatively superficial and thus amenable to live imaging approaches. We performed in vivo time-lapse and longitudinal imaging studies to follow islet development, visualizing both naturally occurring islet cells and cells arising with an accelerated timecourse following an induction approach. These studies revealed previously unappreciated fine dynamic protrusions projecting between neighboring and distant endocrine cells. Using pharmacological compound and toxin interference approaches, and single-cell analysis of morphology and cell dynamics, we determined that endocrine cell motility is regulated by phosphoinositide 3-kinase (PI3K) and G-protein-coupled receptor (GPCR) signaling. Linking cell dynamics to islet formation, perturbation of protrusion formation disrupted endocrine cell coalescence, and correlated with decreased islet cell differentiation. These studies identified novel cell behaviors contributing to islet morphogenesis, and suggest a model in which dynamic exploratory filopodia establish cell-cell contacts that subsequently promote cell clustering.

Summary: Pancreatic endocrine cells extend previously unrecognized dynamic, flexible, fine projections to guide clustering into a compacted islet in a process regulated by PI3K and GPCR.

Long-Term Culture of Self-renewing Pancreatic Progenitors Derived from Human Pluripotent Stem Cells

Pluripotent stem cells have been proposed as an unlimited source of pancreatic β cells for studying and treating diabetes. However, the long, multi-step differentiation protocols used to generate functional β cells inevitably exhibit considerable variability, particularly when applied to pluripotent cells from diverse genetic backgrounds. We have developed culture conditions that support long-term self-renewal of human multipotent pancreatic progenitors, which are developmentally more proximal to the specialized cells of the adult pancreas. These cultured pancreatic progenitor (cPP) cells express key pancreatic transcription factors, including PDX1 and SOX9, and exhibit transcriptomes closely related to their in vivo counterparts. Upon exposure to differentiation cues, cPP cells give rise to pancreatic endocrine, acinar, and ductal lineages, indicating multilineage potency. Furthermore, cPP cells generate insulin+ β-like cells in vitro and in vivo, suggesting that they offer a convenient alternative to pluripotent cells as a source of adult cell types for modeling pancreatic development and diabetes.

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Culture on 3T3 cells enables long-term self-renewal of human pancreatic progenitors

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Proliferation requires EGF, FGF10, retinoic acid, and inhibition of Notch and TGF-β

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Cultured progenitors upregulate genes required for mitosis and telomere maintenance

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Pancreatic duct and β-like cells are generated in vitro and in vivo

EGFR signalling controls cellular fate and pancreatic organogenesis by regulating apicobasal polarity

Apicobasal polarity is known to affect epithelial morphogenesis and cell differentiation, but it remains unknown how these processes are mechanistically orchestrated. We find that ligand-specific EGFR signalling via PI(3)K and Rac1 autonomously modulates apicobasal polarity to enforce the sequential control of morphogenesis and cell differentiation. Initially, EGF controls pancreatic tubulogenesis by negatively regulating apical polarity induction. Subsequently, betacellulin, working via inhibition of atypical protein kinase C (aPKC), causes apical domain constriction within neurogenin3⁺ endocrine progenitors, which results in reduced Notch signalling, increased neurogenin3 expression, and β-cell differentiation. Notably, the ligand-specific EGFR output is not driven at the ligand level, but seems to have evolved in response to stage-specific epithelial influences. The EGFR-mediated control of β-cell differentiation via apical polarity is also conserved in human neurogenin3⁺ cells. We provide insight into how ligand-specific EGFR signalling coordinates epithelial morphogenesis and cell differentiation via apical polarity dynamics.

A radial axis defined by semaphorin-to-neuropilin signaling controls pancreatic islet morphogenesis

The islets of Langerhans are endocrine organs characteristically dispersed throughout the pancreas. During development, endocrine progenitors delaminate, migrate radially and cluster to form islets. Despite the distinctive distribution of islets, spatially localized signals that control islet morphogenesis have not been discovered. Here, we identify a radial signaling axis that instructs developing islet cells to disperse throughout the pancreas. A screen of pancreatic extracellular signals identified factors that stimulated islet cell development. These included semaphorin 3a, a guidance cue in neural development without known functions in the pancreas. In the fetal pancreas, peripheral mesenchymal cells expressed Sema3a, while central nascent islet cells produced the semaphorin receptor neuropilin 2 (Nrp2). Nrp2 mutant islet cells developed in proper numbers, but had defects in migration and were unresponsive to purified Sema3a. Mutant Nrp2 islets aggregated centrally and failed to disperse radially. Thus, Sema3a-Nrp2 signaling along an unrecognized pancreatic developmental axis constitutes a chemoattractant system essential for generating the hallmark morphogenetic properties of pancreatic islets. Unexpectedly, Sema3a- and Nrp2-mediated control of islet morphogenesis is strikingly homologous to mechanisms that regulate radial neuronal migration and cortical lamination in the developing mammalian brain.

The molecular and morphogenetic basis of pancreas organogenesis

The pancreas is an essential endoderm-derived organ that ensures nutrient metabolism via its endocrine and exocrine functions. Here we review the essential processes governing the embryonic and early postnatal development of the pancreas discussing both the mechanisms and molecules controlling progenitor specification, expansion and differentiation. We elaborate on how these processes are orchestrated in space and coordinated with morphogenesis. We draw mainly from experiments conducted in the mouse model but also from investigations in other model organisms, complementing a recent comprehensive review of human pancreas development (Jennings et al., 2015) [1]. The understanding of pancreas development in model organisms provides a framework to interpret how human mutations lead to neonatal diabetes and may contribute to other forms of diabetes and to guide the production of desired pancreatic cell types from pluripotent stem cells for therapeutic purposes.

Epidermal Growth Factor Receptor Signaling Regulates β Cell Proliferation in Adult Mice

A thorough understanding of the signaling pathways involved in the regulation of β cell proliferation is an important initial step in restoring β cell mass in the diabetic patient. Here, we show that epidermal growth factor receptor 1 (EGFR) was significantly up-regulated in the islets of C57BL/6 mice after 50% partial pancreatectomy (PPx), a model for workload-induced β cell proliferation. Specific deletion of EGFR in the β cells of adult mice impaired β cell proliferation at baseline and after 50% PPx, suggesting that the EGFR signaling pathway plays an essential role in adult β cell proliferation. Further analyses showed that β cell-specific depletion of EGFR resulted in impaired expression of cyclin D1 and impaired suppression of p27 after PPx, both of which enhance β cell proliferation. These data highlight the importance of EGFR signaling and its downstream signaling cascade in postnatal β cell growth.

A combination of cytokines EGF and CNTF protects the functional beta cell mass in mice with short-term hyperglycaemia

AIMS/HYPOTHESIS

When the beta cell mass or function declines beyond a critical point, hyperglycaemia arises. Little is known about the potential pathways involved in beta cell rescue. As two cytokines, epidermal growth factor (EGF) and ciliary neurotrophic factor (CNTF), restored a functional beta cell mass in mice with long-term hyperglycaemia by reprogramming acinar cells that transiently expressed neurogenin 3 (NGN3), the current study assesses the effect of these cytokines on the functional beta cell mass after an acute chemical toxic insult.

METHODS

Glycaemia and insulin levels, pro-endocrine gene expression and beta cell origin, as well as the role of signal transducer and activator of transcription 3 (STAT3) signalling, were assessed in EGF+CNTF-treated mice following acute hyperglycaemia.

RESULTS

The mice were hyperglycaemic 1 day following i.v. injection of the beta cell toxin alloxan, when the two cytokines were applied. One week later, 68.6 ± 4.6% of the mice had responded to the cytokine treatment and increased their insulin(+) cell number to 30% that of normoglycaemic control mice, resulting in restoration of euglycaemia. Although insulin(-) NGN3(+) cells appeared following acute EGF+CNTF treatment, genetic lineage tracing showed that the majority of the insulin(+) cells originated from pre-existing beta cells. Beta cell rescue by EGF+CNTF depends on glycaemia rather than on STAT3-induced NGN3 expression in acinar cells.

CONCLUSIONS/INTERPRETATION

In adult mice, EGF+CNTF allows the rescue of beta cells in distress when treatment is given shortly after the diabetogenic insult. The rescued beta cells restore a functional beta cell mass able to control normal blood glucose levels. These findings may provide new insights into compensatory pathways activated early after beta cell loss.

Expression and Function of the Epidermal Growth Factor Receptor in Physiology and Disease

The epidermal growth factor receptor (EGFR) is the prototypical member of a family of membrane-associated intrinsic tyrosine kinase receptors, the ErbB family. EGFR is activated by multiple ligands, including EGF, transforming growth factor (TGF)-α, HB-EGF, betacellulin, amphiregulin, epiregulin, and epigen. EGFR is expressed in multiple organs and plays important roles in proliferation, survival, and differentiation in both development and normal physiology, as well as in pathophysiological conditions. In addition, EGFR transactivation underlies some important biologic consequences in response to many G protein-coupled receptor (GPCR) agonists. Aberrant EGFR activation is a significant factor in development and progression of multiple cancers, which has led to development of mechanism-based therapies with specific receptor antibodies and tyrosine kinase inhibitors. This review highlights the current knowledge about mechanisms and roles of EGFR in physiology and disease.

Prediction of Growth Factor-Dependent Cleft Formation During Branching Morphogenesis Using A Dynamic Graph-Based Growth Model

This study considers the problem of describing and predicting cleft formation during the early stages of branching morphogenesis in mouse submandibular salivary glands (SMG) under the influence of varied concentrations of epidermal growth factors (EGF). Given a time-lapse video of a growing SMG, first we build a descriptive model that captures the underlying biological process and quantifies the ground truth. Tissue-scale (global) and morphological features related to regions of interest (local features) are used to characterize the biological ground truth. Second, we devise a predictive growth model that simulates EGF-modulated branching morphogenesis using a dynamic graph algorithm, which is driven by biological parameters such as EGF concentration, mitosis rate, and cleft progression rate. Given the initial configuration of the SMG, the evolution of the dynamic graph predicts the cleft formation, while maintaining the local structural characteristics of the SMG. We determined that higher EGF concentrations cause the formation of higher number of buds and comparatively shallow cleft depths. Third, we compared the prediction accuracy of our model to the Glazier-Graner-Hogeweg (GGH) model, an on-lattice Monte-Carlo simulation model, under a specific energy function parameter set that allows new rounds of de novo cleft formation. The results demonstrate that the dynamic graph model yields comparable simulations of gland growth to that of the GGH model with a significantly lower computational complexity. Fourth, we enhanced this model to predict the SMG morphology for an EGF concentration without the assistance of a ground truth time-lapse biological video data; this is a substantial benefit of our model over other similar models that are guided and terminated by information regarding the final SMG morphology. Hence, our model is suitable for testing the impact of different biological parameters involved with the process of branching morphogenesis in silico, while reducing the requirement of in vivo experiments.

Short-range growth inhibitory signals from the epithelium can drive non-stereotypic branching in the pancreas

Many organs such as the vasculature, kidney, lungs, pancreas and several other glands form ramified networks of tubes that either maximize exchange surfaces between two compartments or minimize the volume of an organ dedicated to the production and local delivery of a cell-derived product. The structure of these tubular networks can be stereotyped, as in the lungs, or stochastic with large variations between individuals, as in the pancreas. The principles driving stereotyped branching have attracted much attention and several models have been proposed and refined. Here we focus on the pancreas, as a model of non-stereotyped branching. In many ramified tubular organs, an important role of the mesenchyme as a source of branching signals has been proposed, including in the pancreas. However, our previous work has shown that in the absence of mesenchyme, epithelial cells seeded in vitro in Matrigel form heavily branched organoids. Here we experimentally show that pancreatic organoids grow primarily at the tips. Furthermore, in contrast to classical 'depletion of activator' mechanisms, organoids growing in close vicinity seem not to affect each other's growth before they get in contact. We recapitulate these observations in an in silico model of branching assuming a 'local inhibitor' is secreted by the epithelium. Remarkably this simple mechanism is sufficient to generate branched organoids similar to those observed in vitro, including their transition from filled spheres to a tree like structure. Quantifying the similarity between in silico and in vitro development through a normalized surface to volume ratio, our in silico model predicts that inhibition is likely to be cooperative and that the diffusing inhibitor decays within a length scale of 10-20 μm.

Phosphatidic Acid (PA) can Displace PPARα/LXRα Binding to The EGFR Promoter Causing its Transrepression in Luminal Cancer Cells

The expression of the epidermal growth factor receptor (EGFR) is highly regulated in normal cells, whereas some cancer cells have high constitutive levels. Understanding naturally-occurring ways of downregulating EGFR in cancer cells was investigated. Phosphatidic acid (PA) or Nuclear Receptors (NR) PPARα/RXRα/LXRα, enhance EGFR expression, mediated by the promoter region -856(A) to -226(T). Unexpectedly, the combination of NRs and PA caused repression. PA induces a conformational change in the nuclear receptor PPARα (increase of alpha-helices at the expense of decreasing beta-sheets), as evidenced by circular dichroism. This represses the naturally-enhancing capability of PPARα on EGFR transcription. PPARα-overexpressing cells in the presence of PA > 300 nM or the enzyme that produces it, phospholipase D (PLD), downregulate EGFR expression. The reasons are two-fold. First, PA displaces PPARα binding to the EGFR promoter at those concentrations. Second, NR heterodimer-dependent promoter activity is weakened in the presence of PA in vivo. Since other genes considered (β-catenin, cyclin D3, PLD2 and ACOX-1) are also downregulated with a PA + PPARα combination, the transrepression appears to be a global phenomenon. Lastly, the reported effect is greater in MCF-7 than in MDA-MB-231 breast cancer cells, which could provide a novel basis for regulating excessive expression of EGFR in luminal cancer cells.

Myt3 Mediates Laminin-V/Integrin-β1-Induced Islet-Cell Migration via Tgfbi

Myt3 is a prosurvival factor in pancreatic islets; however, its role in islet-cell development is not known. Here, we demonstrate that myelin transcription factor 3 (Myt3) is expressed in migrating islet cells in the developing and neonatal pancreas and thus sought to determine whether Myt3 plays a role in this process. Using an ex vivo model of islet-cell migration, we demonstrate that Myt3 suppression significantly inhibits laminin-V/integrin-β1-dependent α- and β-cell migration onto 804G, and impaired 804G-induced F-actin and E-cadherin redistribution. Exposure of islets to proinflammatory cytokines, which suppress Myt3 expression, had a similar effect, whereas Myt3 overexpression partially rescued the migratory ability of the islet cells. We show that loss of islet-cell migration, due to Myt3 suppression or cytokine exposure, is independent of effects on islet-cell survival or proliferation. Myt3 suppression also had no effect on glucose-induced calcium influx, F-actin remodeling or insulin secretion by β-cells. RNA-sequencing (RNA-seq) analysis of transduced islets showed that Myt3 suppression results in the up-regulation of Tgfbi, a secreted diabetogenic factor thought to impair cellular adhesion. Exposure of islets to exogenous transforming growth factor β-induced (Tgfbi) impaired islet-cell migration similar to Myt3 suppression. Taken together, these data suggest a model by which cytokine-induced Myt3 suppression leads to Tgfbi de-repression and subsequently to impaired islet-cell migration, revealing a novel role for Myt3 in regulating islet-cell migration.

The Basic Helix-Loop-Helix Transcription Factor NEUROG3 Is Required for Development of the Human Endocrine Pancreas

Neurogenin3 (NEUROG3) is a basic helix-loop-helix transcription factor required for development of the endocrine pancreas in mice. In contrast, humans with NEUROG3 mutations are born with endocrine pancreas function, calling into question whether NEUROG3 is required for human endocrine pancreas development. To test this directly, we generated human embryonic stem cell (hESC) lines where both alleles of NEUROG3 were disrupted using CRISPR/Cas9-mediated gene targeting. NEUROG3(-/-) hESC lines efficiently formed pancreatic progenitors but lacked detectible NEUROG3 protein and did not form endocrine cells in vitro. Moreover, NEUROG3(-/-) hESC lines were unable to form mature pancreatic endocrine cells after engraftment of PDX1(+)/NKX6.1(+) pancreatic progenitors into mice. In contrast, a 75-90% knockdown of NEUROG3 caused a reduction, but not a loss, of pancreatic endocrine cell development. We conclude that NEUROG3 is essential for endocrine pancreas development in humans and that as little as 10% NEUROG3 is sufficient for formation of pancreatic endocrine cells.

Efficient generation of NKX6-1+ pancreatic progenitors from multiple human pluripotent stem cell lines

Human pluripotent stem cells (hPSCs) represent a renewable source of pancreatic beta cells for both basic research and therapeutic applications. Given this outstanding potential, significant efforts have been made to identify the signaling pathways that regulate pancreatic development in hPSC differentiation cultures. In this study, we demonstrate that the combination of epidermal growth factor (EGF) and nicotinamide signaling induces the generation of NKX6-1⁺ progenitors from all hPSC lines tested. Furthermore, we show that the size of the NKX6-1⁺ population is regulated by the duration of treatment with retinoic acid, fibroblast growth factor 10 (FGF10), and inhibitors of bone morphogenetic protein (BMP) and hedgehog signaling pathways. When transplanted into NOD scid gamma (NSG) recipients, these progenitors differentiate to give rise to exocrine and endocrine cells, including monohormonal insulin⁺ cells. Together, these findings provide an efficient and reproducible strategy for generating highly enriched populations of hPSC-derived beta cell progenitors for studies aimed at further characterizing their developmental potential in vivo and deciphering the pathways that regulate their maturation in vitro.

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EGF and nicotinamide induce NKX6-1⁺ progenitors from hPSC-derived endoderm

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NKX6-1⁺ progenitor generation can be controlled by the duration of stage 3 treatment

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The generation of polyhormonal cells is dependent on hedgehog signaling inhibition

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NKX6-1⁺ progenitors give rise to ductal, acinar, and endocrine cells in vivo

Matrix metalloproteinase-9 is essential for physiological Beta cell function and islet vascularization in adult mice

The availability of paracrine factors in the islets of Langerhans, and the constitution of the beta cell basement membrane can both be affected by proteolytic enzymes. This study aimed to investigate the effects of the extracellular matrix-degrading enzyme gelatinase B/matrix metalloproteinase-9 (Mmp-9) on islet function in mice. Islet function of Mmp9-deficient (Mmp9(-/-)) mice and their wild-type littermates was evaluated both in vivo and in vitro. The pancreata of Mmp9(-/-) mice did not differ from wild type in islet mass or distribution. However, Mmp9(-/-) mice had an impaired response to a glucose load in vivo, with lower serum insulin levels. The glucose-stimulated insulin secretion was reduced also in vitro in isolated Mmp9(-/-) islets. The vascular density of Mmp9(-/-) islets was lower, and the capillaries had fewer fenestrations, whereas the islet blood flow was threefold higher. These alterations could partly be explained by compensatory changes in the expression of matrix-related proteins. This in-depth investigation of the effects of the loss of MMP-9 function on pancreatic islets uncovers a deteriorated beta cell function that is primarily due to a shift in the beta cell phenotype, but also due to islet vascular aberrations. This likely reflects the importance of a normal islet matrix turnover exerted by MMP-9, and concomitant release of paracrine factors sequestered on the matrix.

In vivo activation of the PI3K-Akt pathway in mouse beta cells by the EGFR mutation L858R protects against diabetes

AIMS/HYPOTHESIS

EGF receptor (EGFR) signalling is required for normal beta cell development and postnatal beta cell proliferation. We tested whether beta cell proliferation can be triggered by EGFR activation at any age and whether this can protect beta cells against apoptosis induced by diabetogenic insults in a mouse model.

METHODS

We generated transgenic mice with doxycycline-inducible expression of constitutively active EGFR (L858R) (CA-EGFR) under the insulin promoter. Mice were given doxycycline at various ages for different time periods, and beta cell proliferation and mass were analysed. Mice were also challenged with streptozotocin and isolated islets exposed to cytokines.

RESULTS

Expression of EGFR (L858R) led to increased phosphorylation of EGFR and Akt in pancreatic islets. CA-EGFR expression during pancreatic development (embryonic day [E]12.5 to postnatal day [P]1) increased beta cell proliferation and mass in newborn mice. However, CA-EGFR expression in adult mice did not affect beta cell mass. Expression of the transgene improved glycaemia and markedly inhibited beta cell apoptosis after a single high dose, as well as after multiple low doses of streptozotocin. In vitro mechanistic studies showed that CA-EGFR protected isolated islets from cytokine-mediated beta cell death, possibly by repressing the proapoptotic protein BCL2-like 11 (BIM).

CONCLUSIONS/INTERPRETATION

Our findings show that the expression of CA-EGFR in the developing, but not in the adult pancreas stimulates beta cell replication and leads to increased beta cell mass. Importantly, CA-EGFR protects beta cells against streptozotocin- and cytokine-induced death.

M2 macrophages promote beta-cell proliferation by up-regulation of SMAD7

Determination of signaling pathways that regulate beta-cell replication is critical for beta-cell therapy. Here, we show that blocking pancreatic macrophage infiltration after pancreatic duct ligation (PDL) completely inhibits beta-cell proliferation. The TGFβ superfamily signaling inhibitor SMAD7 was significantly up-regulated in beta cells after PDL. Beta cells failed to proliferate in response to PDL in beta-cell-specific SMAD7 mutant mice. Forced expression of SMAD7 in beta cells by itself was sufficient to promote beta-cell proliferation in vivo. M2, rather than M1 macrophages, seem to be the inducers of SMAD7-mediated beta-cell proliferation. M2 macrophages not only release TGFβ1 to directly induce up-regulation of SMAD7 in beta cells but also release EGF to activate EGF receptor signaling that inhibits TGFβ1-activated SMAD2 nuclear translocation, resulting in TGFβ signaling inhibition. SMAD7 promotes beta-cell proliferation by increasing CyclinD1 and CyclinD2, and by inducing nuclear exclusion of p27. Our study thus reveals a molecular pathway to potentially increase beta-cell mass through enhanced SMAD7 activity induced by extracellular stimuli.

Human β-cell proliferation and intracellular signaling part 2: still driving in the dark without a road map

Enhancing β-cell proliferation is a major goal for type 1 and type 2 diabetes research. Unraveling the network of β-cell intracellular signaling pathways that promote β-cell replication can provide the tools to address this important task. In a previous Perspectives in Diabetes article, we discussed what was known regarding several important intracellular signaling pathways in rodent β-cells, including the insulin receptor substrate/phosphatidylinositol-3 kinase/Akt (IRS-PI3K-Akt) pathways, glycogen synthase kinase-3 (GSK3) and mammalian target of rapamycin (mTOR) S6 kinase pathways, protein kinase Cζ (PKCζ) pathways, and their downstream cell-cycle molecular targets, and contrasted that ample knowledge to the small amount of complementary data on human β-cell intracellular signaling pathways. In this Perspectives, we summarize additional important information on signaling pathways activated by nutrients, such as glucose; growth factors, such as epidermal growth factor, platelet-derived growth factor, and Wnt; and hormones, such as leptin, estrogen, and progesterone, that are linked to rodent and human β-cell proliferation. With these two Perspectives, we attempt to construct a brief summary of knowledge for β-cell researchers on mitogenic signaling pathways and to emphasize how little is known regarding intracellular events linked to human β-cell replication. This is a critical aspect in the long-term goal of expanding human β-cells for the prevention and/or cure of type 1 and type 2 diabetes.

Transient cytokine treatment induces acinar cell reprogramming and regenerates functional beta cell mass in diabetic mice

Reprogramming of pancreatic exocrine cells into cells resembling beta cells may provide a strategy for treating diabetes. Here we show that transient administration of epidermal growth factor and ciliary neurotrophic factor to adult mice with chronic hyperglycemia efficiently stimulates the conversion of terminally differentiated acinar cells to beta-like cells. Newly generated beta-like cells are epigenetically reprogrammed, functional and glucose responsive, and they reinstate normal glycemic control for up to 248 d. The regenerative process depends on Stat3 signaling and requires a threshold number of Neurogenin 3 (Ngn3)-expressing acinar cells. In contrast to previous work demonstrating in vivo conversion of acinar cells to beta-like cells by viral delivery of exogenous transcription factors, our approach achieves acinar-to-beta-cell reprogramming through transient cytokine exposure rather than genetic modification.

Artificial three-dimensional niches deconstruct pancreas development in vitro

In the context of a cellular therapy for diabetes, methods for pancreatic progenitor expansion and subsequent differentiation into insulin-producing beta cells would be extremely valuable. Here we establish three-dimensional culture conditions in Matrigel that enable the efficient expansion of dissociated mouse embryonic pancreatic progenitors. By manipulating the medium composition we generate either hollow spheres, which are mainly composed of pancreatic progenitors, or complex organoids that spontaneously undergo pancreatic morphogenesis and differentiation. The in vitro maintenance and expansion of pancreatic progenitors require active Notch and FGF signaling, thus recapitulating in vivo niche signaling interactions. Our experiments reveal new aspects of pancreas development, such as a community effect by which small groups of cells better maintain progenitor properties and expand more efficiently than isolated cells, as well as the requirement for three-dimensionality. Finally, growth conditions in chemically defined biomaterials pave the way for testing the biophysical and biochemical properties of the niche that sustains pancreatic progenitors.

The ductal origin of structural and functional heterogeneity between pancreatic islets

Islets form in the pancreas after the first endocrine cells have arisen as either single cells or small cell clusters in the epithelial cords. These cords constitute the developing pancreas in one of its earliest recognizable stages. Islet formation begins at the time the cords transform into a branching ductal system, continues while the ductal system expands, and finally stops before the exocrine tissue of ducts and acini reaches its final expansion. Thus, islets continuously arise from founder cells located in the branching and ramifying ducts. Islets arising from proximal duct cells locate between the exocrine lobules, develop strong autonomic and sensory innervations, and pass their blood to efferent veins (insulo-venous efferent system). Islets arising from cells of more distal ducts locate within the exocrine lobules, respond to nerve impulses ending at neighbouring blood vessels, and pass their blood to the surrounding acini (insulo-acinar portal system). Consequently, the section of the ductal system from which an islet arises determines to a large extent its future neighbouring tissue, architecture, properties, and functions. We note that islets interlobular in position are frequently found in rodents (rats and mice), whereas intralobularly-located, peripheral duct islets prevail in humans and cattle. Also, we expound on bovine foetal Laguesse islets as a prominent foetal type of type 1 interlobular neuro-insular complexes, similar to neuro-insular associations frequently found in rodents. Finally, we consider the probable physiological and pathophysiological implications of the different islet positions within and between species.

Pancreas organogenesis: from lineage determination to morphogenesis

The pancreas is an essential organ for proper nutrient metabolism and has both endocrine and exocrine function. In the past two decades, knowledge of how the pancreas develops during embryogenesis has significantly increased, largely from developmental studies in model organisms. Specifically, the molecular basis of pancreatic lineage decisions and cell differentiation is well studied. Still not well understood are the mechanisms governing three-dimensional morphogenesis of the organ. Strategies to derive transplantable β-cells in vitro for diabetes treatment have benefited from the accumulated knowledge of pancreas development. In this review, we provide an overview of the current understanding of pancreatic lineage determination and organogenesis, and we examine future implications of these findings for treatment of diabetes mellitus through cell replacement.

Sympathetic innervation during development is necessary for pancreatic islet architecture and functional maturation

Sympathetic neurons depend on target-derived neurotrophic cues to control their survival and growth. However, whether sympathetic innervation contributes reciprocally to the development of target tissues is less clear. Here, we report that sympathetic innervation is necessary for the formation of the pancreatic islets of Langerhans and for their functional maturation. Genetic or pharmacological ablation of sympathetic innervation during development resulted in altered islet architecture, reduced insulin secretion, and impaired glucose tolerance in mice. Similar defects were observed with pharmacological blockade of β-adrenergic signaling. Conversely, the administration of a β-adrenergic agonist restored islet morphology and glucose tolerance in deinnervated animals. Furthermore, in neuron-islet cocultures, sympathetic neurons promoted islet cell migration in a β-adrenergic-dependent manner. This study reveals that islet architecture requires extrinsic inductive cues from neighboring tissues such as sympathetic nerves and suggests that early perturbations in sympathetic innervation might underlie metabolic disorders.

The neuregulin system of ligands and their receptors in rat islets of langerhans

Islet cell growth and function are affected by ligands from the epidermal growth factor (EGF) family. We describe here the expression, regional distribution, and effect on growth and secretion of insulin of a subset of these, the neuregulin (NRG) family. The expression of NRG1α, NRG1β, NRG2α, NRG2β, NRG3, and NRG4 in rat islets was determined using immunohistochemical and double immunofluorescent staining. We also report the expression of the 4 receptors and the remaining 7 ligands using immunohistochemistry. The NRG1α splice variant was expressed in β-cells and the NRG1β variant mainly in α-cells. NRG3 was also predominantly present in α-cells. Most of the members of the EGF family of ligands were also expressed, with Epigen being present at the highest levels. The rat islet-derived cell line CRI-G1 was used to study the effect of addition of EGF, NRG1β, NRG3, and NRG4 on cell growth and insulin secretion. Synthetic refolded NRG3 strongly stimulated the growth of the CRI-G1 cells, and NRG4 gave the greatest stimulation of insulin release. Different members of the NRG family are therefore potentially potent stimuli for islet cell growth and insulin release and differ in expression in α- and β-cells.

Matrix metalloproteinase-9 reduces islet amyloid formation by degrading islet amyloid polypeptide

Deposition of islet amyloid polypeptide (IAPP) as amyloid is a pathological hallmark of the islet in type 2 diabetes, which is toxic to β-cells. We previously showed that the enzyme neprilysin reduces islet amyloid deposition and thereby reduces β-cell apoptosis, by inhibiting fibril formation. Two other enzymes, matrix metalloproteinase (MMP)-2 and MMP-9, are extracellular gelatinases capable of degrading another amyloidogenic peptide, Aβ, the constituent of amyloid deposits in Alzheimer disease. We therefore investigated whether MMP-2 and MMP-9 play a role in reducing islet amyloid deposition. MMP-2 and MMP-9 mRNA were present in mouse islets but only MMP-9 activity was detectable. In an islet culture model where human IAPP (hIAPP) transgenic mouse islets develop amyloid but nontransgenic islets do not, a broad spectrum MMP inhibitor (GM6001) and an MMP-2/9 inhibitor increased amyloid formation and the resultant β-cell apoptosis. In contrast, a specific MMP-2 inhibitor had no effect on either amyloid deposition or β-cell apoptosis. Mass spectrometry demonstrated that MMP-9 degraded amyloidogenic hIAPP but not nonamyloidogenic mouse IAPP. Thus, MMP-9 constitutes an endogenous islet protease that limits islet amyloid deposition and its toxic effects via degradation of hIAPP. Because islet MMP-9 mRNA levels are decreased in type 2 diabetic subjects, islet MMP-9 activity may also be decreased in human type 2 diabetes, thereby contributing to increased islet amyloid deposition and β-cell loss. Approaches to increase islet MMP-9 activity could reduce or prevent amyloid deposition and its toxic effects in type 2 diabetes.

The relation among NGF, EGF and insulin is important for triggering pancreatic β cell apoptosis

BACKGROUND

Nerve growth factor (NGF) is a well-known mediator for maintaining the survival of neurons, while recent studies report that its absence induces apoptosis in cultured β cells of humans and rats. However, its relationship with other growth factors that have important roles in the survival and function of β cells such as epidermal growth factor (EGF) has not yet been elucidated. The aim of this study was to investigate the effects of NGF withdrawal on the synthesis and secretion of EGF, insulin with respect to β cell apoptosis in hyperglycemic rats.

METHOD

β cells were isolated from euglycemic and streptozotocin-induced hyperglycemic rats and treated with NGF neutralizing antibody for withdrawal of NGF in culture medium. NGF, EGF and insulin levels in cell lysates and secretion samples were measured by enzyme-linked immunosorbent assay, and their gene expressions were determined by real-time reverse transcription polymerase chain reaction assay. Apoptosis was quantitatively determined by cytoplasmic histone-associated DNA fragments.

RESULTS

Nerve growth factor neutralization triggered β cell apoptosis. In addition decreased insulin, increased NGF and EGF were observed at gene expression and protein levels by NGF neutralization. Moreover, NGF withdrawal decreased secretion of these peptides from β cells. Although the alterations seemed to be similar under euglycemic and hyperglycemic conditions, NGF withdrawal more strongly affected β cells of hyperglycemic rats.

CONCLUSIONS

These important findings indicate that NGF is an important regulator for the synthesis and secretion of EGF and insulin from the β cells. Moreover, results suggested that NGF withdrawal causes apoptosis by decreasing EGF, NGF and insulin secretion from β cells of hyperglycemic rats.